Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (2024)

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Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (3)

Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (4)

Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (5)

Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (6)

Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (7)

Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (8)

Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (9)

Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (10)

Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (11)

Roy E Hunt - Geotechnical Investigation Methods A Field Guide for Geotechnical Engineers-CRC Press (2006) - Mecânica dos Solos (12)

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GEOTECHNICAL INVESTIGATION METHODSA Field Guide for Geotechnical EngineersCRC_42742_FM_pii.qxd 9/19/2006 9:49 AM Page iiGEOTECHNICAL INVESTIGATION METHODSA Field Guide for Geotechnical EngineersRoy E. Hunt, P.E., P.G.The material was previously published in Geotechnical Engineering Investigations Handbook, Second Edition ©CRC Press LLC 2005.CRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487‑2742© 2007 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa businessNo claim to original U.S. Government worksPrinted in the United States of America on acid‑free paper10 9 8 7 6 5 4 3 2 1International Standard Book Number‑10: 1‑4200‑4274‑2 (Hardcover)International Standard Book Number‑13: 978‑1‑4200‑4274‑0 (Hardcover)This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any informa‑tion storage or retrieval system, without written permission from the publishers.For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978‑750‑8400. CCC is a not‑for‑profit organization that provides licenses and registration for a variety of users. For orga‑nizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged.Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe.Library of Congress Cataloging‑in‑Publication DataHunt, Roy E.Geotechnical investigation methods : a field guide for geotechnical engineers / by Roy E. Hunt.p. cm.Includes bibliographical references.ISBN 1‑4200‑4274‑2 (alk. paper)1. Engineering geology‑‑Handbooks, manuals, etc. 2. Earthwork. I. Title. TA705.H865 2006624.1’51‑‑dc22 2006048956Visit the Taylor & Francis Web site athttp://www.taylorandfrancis.comand the CRC Press Web site athttp://www.crcpress.comContentsINTRODUCTION ..........................................................................................................................1Chapter 1. Exploration..............................................................................................................31.1 Introduction ............................................................................................................................31.1.1 Objectives ..................................................................................................................31.1.2 Methodology..............................................................................................................31.1.3 Scope ..........................................................................................................................31.2 Surface Mapping....................................................................................................................51.2.1 General........................................................................................................................51.2.2 Research Data ............................................................................................................51.2.3 Remotely Sensed Imagery ......................................................................................91.2.4 Terrain Analysis ......................................................................................................161.2.5 Site Reconnaissance ................................................................................................291.2.6 Preparation of Subsurface Exploration Program ..............................................311.3 Subsurface Exploration ......................................................................................................311.3.1 General......................................................................................................................311.3.2 Geophysical methods ............................................................................................321.3.3 Reconnaissance Methods ......................................................................................541.3.4 Continuous CPT(ASTM D5778)............................................................................541.3.5 Test and Core Borings ............................................................................................621.3.6 Borehole Remote-Sensing and Logging ..............................................................811.3.7 Groundwater and Seepage Detection..................................................................841.4 Recovery of Samples and Cores ........................................................................................871.4.1 General......................................................................................................................871.4.2 Test Boring Soil Sampling......................................................................................891.4.3 Miscellaneous Soil-Sampling Methods................................................................971.4.4 Subaqueous Sampling............................................................................................991.4.5 Rock Coring ..........................................................................................................1021.4.6 Sample and Core Treatment ................................................................................1141.4.7 Data Presentation ..................................................................................................119References ....................................................................................................................................123Further Reading ..........................................................................................................................125Chapter 2. Measurement of Properties ............................................................................1272.1 Introduction ........................................................................................................................1272.1.1 Objectives ..............................................................................................................1272.1.2 Geotechnical Properties ......................................................................................1272.1.3 Testing Methods Summarized ............................................................................1282.2 Basic and Index Properties ..............................................................................................1352.2.1 Intact Rock ............................................................................................................1352.2.2 Rock Masses ..........................................................................................................1382.2.3 Soils ........................................................................................................................139CRC_42742_FM.qxd 9/19/2006 9:27 AM Page v2.3 Hydraulic Properties (Permeability) ..............................................................................1512.3.1 Introduction ..........................................................................................................1512.3.2 Estimating the Permeability Coefficient k ........................................................1522.3.3 Laboratory Tests ....................................................................................................1542.3.4 In Situ Testing ........................................................................................................1582.4 Rupture Strength................................................................................................................1622.4.1 Introduction ..........................................................................................................1622.4.2 Shear Strength Relationships ..............................................................................1672.4.3 Rock Strength Measurements ............................................................................1792.4.4 Soil Strength Measurements................................................................................1872.4.5 Soil Penetration Tests............................................................................................1992.5 Deformation without Rupture ........................................................................................2062.5.1 Introduction ..........................................................................................................2062.5.2 Deformation Relationships ..................................................................................2112.5.3 Rock Deformation Measurements......................................................................2152.5.4 Soil Deformation Measurements (Static) ..........................................................2232.5.5 Dynamic Deformation Moduli (Soils) ..............................................................2392.6 Typical Values of Basic, Index, and Engineering Properties ......................................2422.6.1 Rock Masses ..........................................................................................................2422.6.2 Weathered Rock and Residual Soil ....................................................................2432.6.3 Cohesionless Soils ................................................................................................2432.6.4 Clay Soils................................................................................................................2432.6.5 Compacted Materials ..........................................................................................251References ....................................................................................................................................251Further Reading ..........................................................................................................................257Chapter 3. Field Instrumentation ......................................................................................2593.1 Introduction ........................................................................................................................2593.1.1 Methods and Instruments Summarized............................................................2593.1.2 Objectives ..............................................................................................................2593.1.3 Applications ..........................................................................................................2593.1.4 Program Elements ................................................................................................2633.1.5 Transducers ............................................................................................................2653.2 Surface Movements ..........................................................................................................2673.2.1 Forms and Significance ........................................................................................2673.2.2 Surveying ..............................................................................................................2693.2.3 Tiltmeters................................................................................................................2733.2.4 Extensometers........................................................................................................2753.2.5 Vibration Monitoring............................................................................................2783.3 Subsurface Deformations ................................................................................................2793.3.1 Forms and Significance ........................................................................................2793.3.2 Vertical Displacement ..........................................................................................2803.3.3 Lateral Displacement............................................................................................2853.3.4 Linear Strain Gradients ........................................................................................2903.3.5 Acoustical Emissions............................................................................................2923.4 In Situ Pressures and Stresses ..........................................................................................2963.4.1 General....................................................................................................................2963.4.2 Pore-Water Pressures............................................................................................2973.4.3 Loads and Stresses ................................................................................................3023.4.4 Residual Rock Stresses ........................................................................................305CRC_42742_FM.qxd 9/19/2006 9:27 AM Page vi3.5 Instrumentation Arrays for Typical Problems ..............................................................3083.5.1 Importance ............................................................................................................3083.5.2 Settlement of Structures ......................................................................................3083.5.3 Excavation Retention ............................................................................................3113.5.4 Earth Dams ............................................................................................................3123.5.5 Tunnels, Caverns, and Mines ..............................................................................3143.5.6 Natural and Cut Slopes........................................................................................3173.5.7 Fault Movements ..................................................................................................320References ....................................................................................................................................320Further Reading ..........................................................................................................................322Catalogs ........................................................................................................................................322Appendix A. The Earth and Geologic History ................................................................323A.1 Significance to the Engineer ............................................................................................323A.2 The Earth ............................................................................................................................323A.2.1 General ..................................................................................................................323A.2.2 Cross Section ........................................................................................................323A.3 Global Tectonics ................................................................................................................324A.3.1 General ..................................................................................................................324A.3.2 The Hypotheses ....................................................................................................324A.4 Geologic History ..............................................................................................................325A.4.1 North America: Provides a General Illustration ............................................325A.4.2 Radiometric Dating ............................................................................................328References ....................................................................................................................................329Further Reading ..........................................................................................................................329Index ............................................................................................................................................331CRC_42742_FM.qxd 9/19/2006 9:27 AM Page viiCRC_42742_FM.qxd 9/19/2006 9:27 AM Page viii1IntroductionPurpose and ScopeThis book describes and provides the basis for the selection of the numerous methods andprocedures for:1. Exploring the geologic environment and mapping surficial conditions, includingrock, soil, water, and geologic hazards; preparing subsurface sections; andobtaining samples of the materials for identification, classification, and labora-tory testing.2. Measurement of material properties (basic, index, hydraulic, and mechanical) inthe field and laboratory. 3. Field instrumentation to measure and monitor movements, deformations, andstresses occurring naturally or as a consequence of construction.Although, in practice, analytical procedures and design criteria are often presented as partof an investigation, they are not included within the scope of this book.SignificanceThe investigation phase of any geotechnical study undertaken for development, construc-tion, or any other engineering works is by far the most important phase. Not only mustconditions at the project site be thoroughly identified, but for many projects, the regionalgeologic characteristics must also be determined. For all phases of investigation, there area large number of methods and devices to choose from, ranging from simple to complex,and usually several are applicable for a given subject of study.Geotechnical engineering analyses and evaluations are valid only when based onproperties truly representing all of the natural materials that may influence the works.Properties of some materials are best measured in the laboratory, while others must befield tested. In some cases, properties cannot be adequately defined by direct testingand the result will be designs that are conservative and too costly, unconservative andrisky, or unconservative but based on contingency plans. To monitor ground conditionsCRC_42742_Intro.qxd 9/21/2006 5:28 PM Page 1during construction, field instrumentation is an important element of many studies,where subsurface conditions cannot be adequately defined by exploration and testing.Instrumentation is used also to obtain design data and to monitor changing naturalconditions such as slope failures and fault movements.2 Geotechnical Investigation MethodsCRC_42742_Intro.qxd 9/21/2006 5:28 PM Page 21Exploration1.1 Introduction1.1.1 ObjectivesThe general objective of an exploration program is to identify all of the significant featuresof the geologic environment that may impact on the proposed construction. Specific objec-tives are to:1. Define the lateral distribution and thickness of soil and rock strata within thezone of influence of the proposed construction.2. Define groundwater conditions considering seasonal changes and the effects ofconstruction or development extraction.3. Identify geologic hazards, such as unstable slopes, faults, ground subsidence andcollapse, floodplains, regional seismicity, and lahars.4. Procure samples of geologic materials for the identification, classification, andmeasurement of engineering properties.5. Perform in situ testing to measure the engineering properties of the geologicmaterials (Chapter 2).1.1.2 MethodologyThree general categories subdivide exploration methodology:1. Surface mapping of geologic conditions (Section 1.2), which requires review ofreports and publications, interpretation of topographic and geographic maps,remote-sensing imagery, and site reconnaissance2. Subsurface sectioning (Section 1.3), for which data are obtained by geophysicalprospecting, test and core borings, and excavations and soundings3. Sampling the geologic materials (Section 1.4) utilizing test and core borings andexcavationsA general summary of exploration methods and objectives is given in Table 1.1.1.1.3 ScopeThe scope of the investigation will depend upon the size of the proposed constructionarea, i.e., a building footprint, or several to hundreds of acres, or square miles, and the3CRC_42742_Ch001.qxd 9/21/2006 5:36 PM Page 34 Geotechnical Investigation MethodsTABLE 1.1Exploration Objectives and Applicable MethodsObjectivesGeneralGeophysicsBoringBorehole Sensing MiscellaneousGeologyRegionalXXXXXSurficial-landXXXXXSurficial-seafloorXXXXMajor structuresXXXXXXXXFaultsaXXXXXXXXXXXXXXXXXSectionsDeep-landXXXXXXShallow-landXXXXXXXXXXXXXXXXXXSubaqueousXXXXXXSoft-soil depthXXXXXXSliding massesaXXXXXXXXXRock depthXXXXXXXRock-massconditionsXXXXXXXXXXXXSoil samplesDisturbed to GWLXXXXXXXRepresentativeXXXXUndisturbedXXXXDeep, offshoreXXRock coresNormal depthsXDeepXaSee also Instrumentation.Bucket AugerHand AugersContinuous Cone PenetrometerRetractable PlugBar SoundingsAditsTest Pits/Trenches3-D Velocity LogUltrasonic AcousticsRadioactive ProbesElectric Well LogAcoustical SoundingBorehole CamerasWire-Line DrillingHollow-Stem AugerContinuous-Flight AugerRotary ProbeRotary DrillingWash BoringVideo-Pulse RadarRadar ProfilingMagnetometerGravimeterElectrical MethodsSeismic ReflectionSeismic RefractionReconnaissanceUnderwater TVSide-Scan SonarBathymetryImagery: Low-Altitude PhotosImagery: Satellite, SLARTopographic MapsReports and PublicationsCRC_42742_Ch001.qxd 9/21/2006 5:36 PM Page 4experience of the investigator in the area. Do they have prior knowledge or is the area newto them? This text basically assumes that prior knowledge is nil or limited.1.2 Surface Mapping1.2.1 GeneralObjectivesData BaseFor all sites it is important to determine the general geologic conditions and identify sig-nificant development and construction constraints. For large study areas it is useful to pre-pare a map illustrating the surficial and shallow geologic conditions.Preliminary Site EvaluationsAn overview of geologic conditions permits preliminary evaluations regarding the suit-ability of the site for development. The first step is the identification of major geologic haz-ards and “constraints” in the study area. Depending upon the construction or developmentproposed, constraints could include shallow rock or water, or thick deposits of weak soils.Taking into account the hazards and constraints, the optimum location for the proposedconstruction is selected, and the planning of the site investigation then begins.MethodologyA geologicreconnaissance study may advance through a number of steps as describedbriefly in Figure 1.1, including:● Research of reference materials and collection of available data.● Terrain analysis based on topographic maps and the interpretation of remotelysensed imagery.● Preparation of a preliminary engineering geology map (large land areas).● Site reconnaissance to confirm initial data, and, for large areas, amplification ofthe engineering geology map, after which it is prepared in final form.● Preparation of a subsurface exploration program based on the anticipated conditions.1.2.2 Research DataBasic ObjectivesA large amount of information is often available in the literature for a given location. Asearch should be made to gather as much data as possible before initiating any explorationwork, particularly when large sites are to be studied, or when the site is located in a regionnot familiar to the design team. Information should be obtained on:● Bedrock geology, including major structural features such as faults.● Surficial geology in terms of soil types on a regional or, if possible, local basis.● Climatic conditions, which influence soil development, groundwater occurrenceand fluctuations, erosion, flooding, slope failures, etc.● Regional seismicity and earthquake history.Exploration 5CRC_42742_Ch001.qxd 9/21/2006 5:36 PM Page 5● Geologic hazards, both regional and local, such as ground subsidence and col-lapse, slope failures, floods, and lahars.● Geologic constraints, both regional and local, such as expansive soils, weak soils,shallow rock, groundwater, etc.Information SourcesGeologic texts provide information on physiography, geomorphology, and geologic forma-tion types and structures, although usually on a regional basis.Federal and state agencies issue professional papers, bulletins, reports, and geologic maps,as do some cities. Sources of geologic information include the U.S. Geological Survey(USGS) and the U.S. State geological departments. Agencies for agriculture, mining, andgroundwater also issue reports, bulletins, and maps. Information on the USGS and StateAgencies can be found on the Internet.Engineering soil surveys have been prepared for New Jersey (Rogers, 1950) and Rhode Island,which are presented as reports and maps on a county basis. The maps illustrate shallow soiland rock conditions and the soils are classified by origin in combination with AASHODesignation M145–49. The prevailing or average drainage conditions are also shown.Technical publications such as the journals of the American Society of Civil Engineers,Institute of Civil Engineers (London), the Association of Engineering Geologists (USA),the Canadian Geotechnical Journal, and the various international conferences on soil androck mechanics, engineering geology, and earthquakes, often contain geologic informationon a specific location.Climatic data are obtained from the U.S. Weather Bureau or other meteorological agencies.Geologic MapsGeologic maps generally vary in scale from 1:2,500,000 (U.S. map) to various scales used bystate agencies, to USGS quadrangle maps at 1:24,000, and vary in the type of geologic infor-mation provided. A guide to map scale conversions is given in Table 1.2. On a worldwidebasis the availability of geologic maps varies from excellent in modern, developed coun-tries, to poor to nonexistent in other countries or areas.6 Geotechnical Investigation MethodsData collection AnalysisReview1. Geologic data Reports: Geology and groundwater Maps: Surficial, bedrock, structural, soil surveys2. Soil/rock engineering data Technical publications, reports from public agencies, private correspondence, for boring logs, maps, laboratory dataPrepare preliminaryengineering geology mapField reconnaissanceof sitePrepare finalengineering geology mapIncorporate fieldobservations andreanalyze landformdataProgram explorationsCheck boundariesGeologic sectionsSamplesIn situ testing3. Terrain analysis data a. Large area or seismic study: (1) Topographic maps: 1:100,000; 1:50,000; and 1:25,000 (2) Imagery: LANDSAT 1:1,000,000 and 1:125,000 SLAR 1:125,000 Photos (U-2 or RB-57) 1:125,000 Photos 1:40,000 and 1:20,000 b. Small area study (nonseismic) (1) Topographic maps: 1:50,000; 1:25,000 and 1:10,000 (2) Imagery (photos); 1:40,000 or 1:20,000 and 1:10,000Soil types Drainage Rock type/depth Rock structure features Groundwater depth Hazards identified: Slides Sinkholes Faults FloodplainsSurface exposures of soil/rockCutsRiver banksExcavationsQuarries/pitsSlopesPlot on preliminarymap, make sketches, take photosIdentify featuresfor reconnainssance Hazards, cuts, quarries, etc.ReviewAnalysisSitereconnaissanceFinal mappreparationProgramexplorationsPreliminaryinterpretationFIGURE 1.1The elements of the geologic land reconnaissance study.CRC_42742_Ch001.qxd 9/21/2006 5:36 PM Page 6Bedrock geology maps (Figure 1.2) often provide only the geologic age; the rock types areusually described in an accompanying text. There is a general correlation between geo-logic age and rock type. The geologic time scale and the dominant rock types in NorthAmerica for the various time periods are given in Appendix A. The formations for a givenperiod are often similar in other continents. For the purpose of mapping, rocks are dividedinto formations, series, systems, and groups. Formation is the basic unit; it has recogniza-ble contacts to enable tracing in the field and is large enough to be shown on the map.Series are coordinate with epochs, systems with periods, and the largest division, groups,with eras.Structural geology may be shown on special maps or included on bedrock geology mapsusing symbols that identify faults, folding, bedding, jointing, foliation, and cleavage. Themaps often include geologic columns and sections. Surficial geology maps depict shallow or surficial soil and rock types.Exploration 7TABLE 1.2Guide to Map ScalesScale ft/in. in./1000 ft in./mile miles/in. m/in. acres/in.21:500 41.67 24.00 126.72 0.008 12.70 0.0401:600 50.00 20.00 105.60 0.009 15.24 0.0571:1000 83.33 12.00 63.36 0.016 25.40 0.1591:1200 100.00 10.00 52.80 0.019 30.48 0.2301:1500 125.00 8.00 42.24 0.024 38.10 0.3591:2000 166.67 6.00 31.68 0.032 50.80 0.6381:2400 200.00 5.00 26.40 0.038 60.96 0.9181:2500 208.33 4.80 25.34 0.039 63.50 0.9961:3000 250.00 4.00 21.12 0.047 76.20 1.4351:4000 333.33 3.00 15.84 0.063 101.60 2.5511:5000 416.67 2.40 12.67 0.079 127.00 3.9861:6000 500.00 2.00 10.56 0.095 152.40 5.7391:7920 660.00 1.515 8.00 0.125 201.17 10.0001:8000 666.67 1.500 7.92 0.126 203.20 10.2031:9600 800.00 1.250 6.60 0.152 243.84 14.6921:10000 833.33 1.200 6.336 0.158 254.00 15.9421:12000 1,000.00 1.000 5.280 0.189 304.80 22.9571:15000 1,250.00 0.800 4.224 0.237 381.00 35.8701:15840 1,320.00 0.758 4.000 0.250 402.34 40.0001:19200 1,600.00 0.625 3.300 0.303 487.68 58.7701:20000 1,666.67 0.600 3.168 0.316 508.00 63.7691:21120 1,760.00 0.568 3.000 0.333 536.45 71.1111:24000 2,000.00 0.500 2.40 0.379 609.60 91.8271:25000 2,083.33 0.480 2.534 0.305 635.00 99.6391:31680 2,640.00 0.379 2.000 0.500 804.67 160.0001:48000 4,000.00 0.250 1.320 0.758 1,219.20 367.3091:62500 5,208.33 0.192 1.014 0.986 1,587.50 622.7441:63360 5,280.00 0.189 1.000 1.000 1,609.35 640.0001:100000 8,333.33 0.120 0.634 1.578 2,540.00 1,594.2251:125000 10,416.67 0.096 0.507 1.973 3,175.01 2,490.9801:126720 10,560.00 0.095 0.500 2.000 3,218.69 2,560.0001:250000 20,833.33 0.048 0.253 3.946 6,350.01 9,963.9071:253440 21,120.00 0.047 0.250 4.000 6,437.39 10,244.2021:500000 41,666.67 0.024 0.127 7.891 12,700.02 39,855.6271:750000 62,500.00 0.016 0.084 11.837 19,050.04 89,675.1611:1000000 83,333.33 0.012 0.063 15.783 25,400.05 159,422.507Formula Scale 12.000 63.360 Scale ft/in.� (Scale)212 Scale Scale 63.360 0.3046 43,560� 144CRC_42742_Ch001.qxd 9/21/2006 5:36 PM Page 78 Geotechnical Investigation MethodsFIGURE 1.2Geology map of northern New Jersey. (From New Jersey Geological Survey, 1994.)CRC_42742_Ch001.qxd 9/21/2006 5:36 PM Page 8Folios of the Geologic Atlas of the United States was produced by the USGS until 1945.Detailed maps of bedrock geology, structural geology, and surficial geology for manycities in the United States and other areas of major geologic importance were included.Soil survey maps, produced by the Soil Conservation Service (SCS) of the U.S. Department ofAgriculture, are usually plotted as overlays on aerial photographs at relatively large scales.Prepared on a county basis they show the soil cover to a depth of about 6 ft (2 m), based onpedological soil classifications. They are often combined with symbology describing slopes,shallow groundwater, and soil drainage conditions. Recent maps contain engineering-oriented data prepared by the Bureau of Public Roads in conjunction with the SCS. However,the shallow depth depicted limits their usefulness in many engineering studies.Flood insurance maps identify 100- and 500-year-old floodplains adjacent to water bodies.These are available from the Federal Emergency Management Agency (FEMA), the USGS,and State Agencies.Tectonic maps give regional lineations often indicative of faulting.Earthquake data may be presented as intensity maps, isoseismal maps, various forms ofseismic risk maps, or as microzonation maps.Other useful maps published by the Geological Society of America include the glacial mapof the United States and the loessial soils or wind-blown deposits of the United States.Topographic Maps and ChartsTopographic maps, such as quadrangle sheets, show landforms, drainage patterns, streamshapes, and surface water conditions, all indicators of geologic conditions. Because of theiravailability and usefulness they should be procured as a first step in any study. They areavailable from a number of sources and in a variety of scales as follows:● USGS provides maps covering a quadrangle area bounded by lines of latitudeand longitude available in 7.5° series (1:24,000) (Figure 1.3), 15° series (1:62,500),30° series (1:125,000), and 1° series (1:250,000) for most of the United States,although many of the larger scales are out of print.● Other countries use scales ranging from 1:10,000 to 1:1,000,000 but coverage isoften incomplete. 1:50,000 is a common scale available for many areas, even incountries not fully developed.Coastline charts, available from the National Ocean Service (NOAA-NOS), provide infor-mation on water depths and near-shore topography.Remotely Sensed ImageryRemote-sensing platforms now include satellite-borne digital imagery and radar sys-tems, airborne imagery including digital and radar imagery, and aerial photography. Inrecent years, many new sources of remotely sensed imagery have been, and continue tobe, developed. The relationship between the various forms and the electromagnetic spec-trum is given in Figure 1.4. Remotely sensed imagery is discussed in the following section.1.2.3 Remotely Sensed ImagerySatellite Imagery (Digital Sensors)Satellite-borne systems obtain images of the Earth’s entire surface every 16 days butimages are affected by cloud cover:● LANDSAT (USA-NASA): Landsat satellites have been launched periodicallysince the first satellite (ERTS) was launched in 1972. Landsat 7, launched in 1999,Exploration 9CRC_42742_Ch001.qxd 9/21/2006 5:36 PM Page 9includes a multispectral scanner (MSS) system and an enhanced thematic mapper(ETM) system. The MSS system, with a spatial resolution of 79 m, has four chan-nels that record reflected solar energy corresponding to green and red bands andtwo near-infrared spectroscopy (NIR) spectral regions. A fifth channel, with a spa-tial resolution of 240 m, records emitted energy in the thermal infrared region.The ETM system, with a spatial resolution of 30 m, collects reflected energy inthree visible bands and three infrared bands. The system has one thermal infraredchannel with 60-m spatial resolution. Also included is a panchromatic (black andwhite) channel with a spatial resolution of 15 m. Swath width is 185�185 km. 3-D stereo-projections can be prepared from sequentially obtained images.(Examples of satellite images are given in Figure 1.5).● SPOT (France): First launched in 1986, SPOT now includes a high-resolutionvisible sensor and a multispectral sensor with a spatial resolution of 10 m. 10 Geotechnical Investigation Methods160Route 23WallkillriverHamburgFeet x 100Feet x 100140120100806040200 0 2040 6080 100120 140(a) (b)FIGURE 1.3(a) Portion of USGS Hamburg NJ Quad Sheet, Scale 1” � 2000� (1:24000). Area has been glaciated. Shown aregeneral bedrock types. Note relation to landform shown on inset as evidenced by topography. (b) 3-D diagramof topography of Figure 1.3a. (Courtesy of USGS.)CRC_42742_Ch001.qxd 9/21/2006 5:36 PM Page 10The panchromatic mode has a spatial resolution of 5 m. Swath width is 60 � 60 km.SPOT is capable of acquiring stereocoptic (overlapping) imagery.● IKONOS, Quick Bird (DigitalGlobe), and OrbView-3 (Orbimage) are recentlylaunched U.S. satellites that are reported to have a multispectral spatial resolu-tion of 4 m and a panchromatic spatial resolution of 1 m. Swath width is of theorder of 8�8 km.● Other countries including India, Russia, Japan, and China have also launchedsatellites.Satellite Imagery (Radar Sensors)● SAR (synthetic aperture radar) images have been obtained by the European SpaceAgency with satellites ERS-1 and ERS-2 since 1992. Since SAR is based onreflected signals from radio waves, images can be obtained during day or night,and through cloud cover. ● InSAR (interferometric SAR), is also known as DifSAR (differential synthetic aper-ture radar interferometry). Using two different satellite passes and applying acomplex and computer-intensive process, an interferogram is created. Becauseof precise, specific geometry, the sources combine to create bright and dark pat-terns of interference or “fringes,” which can be converted to ground heightswith a precision reported down to 0.7 cm possible. The images are color-enhanced using filters to produce color-coded interferograms. They have beenused to record ground subsidence over large areas (Professional Surveyor,1999).Airborne Imagery (Digital Sensors)● Airborne digital imagery is obtained from aircraft flying at less than 3000 m. Data pro-curement is normally on a site-, time-, and weather-specific basis and sequentialExploration 11Sensing instrumentsGamma rayX-rayUltravioletNear infraredThermalbandVisibleInfraredMicrowaveRadarPassive microwaveHuman eyeThermal scannersBlackbody at 5800 KUVBlueGreenRedIRBlackbody at 1200 KBlackbody at 600 KBlackbody at 300 KBlocking effect of atmosphereSun's energyPhotographyMultispectral scannersRadioRadarK bandX bandC bandP bandVisiblePercent transmissionEnergy0.03 Å0.03 Å0.3 µ0.4 µ0.5 µ0.6 µ1 µ0.7 µ0.3 Å3 Å30 Å300 Å(3 µm)0.2 µ(30 µm)(200 µm)(1000 µm)2 µ4 µ6 µ10 µ20 µ40 µ60 µ100 µ200 µ0.5 mm1 mm1 cm 1 m10 m1 cm 1 m10 m100 m0.3 Å 3 Å 30 Å 300 Å 0.2 µ 0.3 µ 0.4 µ 0.5 µ 0.6 µ 0.7 µ 1 µ2 µ4 µ6 µ10 µ20 µ40 µ60 µ100 µ200 µ0.5 mm1 mmFIGURE 1.4The electromagnetic spectrum illustrating atmospheric attenuation and general sensor categories. (From Way,D.S. Terrain Analysis, 2nd ed., Dowden, Hutchinson & Ross, Stroudsburg, Pennsylvania, 1978.)CRC_42742_Ch001.qxd9/21/2006 5:36 PM Page 11missions are practical. One imaging system available is composed of a digital camera, onboard GPS, and inertial measurement unit. The digital camera collectsimagery in three bands and can provide both true color and color infrared. Images are obtained with resolutions of 0.3 to 1 m, and stereo-images are possible(Professional Surveyor, 2002).Airborne Imagery (Radar Sensors)● SLAR (side-looking airborne radar, real-aperture system) has been in use for manyyears. It penetrates cloud cover and to some degree vegetation, providing low-resolution images normally at scales of 1:125,000 to 1:100,000, and occasionallysmaller (see Figure 1.6). Worldwide coverage, including the United States, isspotty.● LiDAR (light detection and ranging, or laser radar; GPS based): This airborne systemsends out pulses of laser energy to the ground surface that reflect the energy, pro-viding a measure of the distance. The beams rebound to sensitive detectors in theaircraft where the resulting data are analyzed with a computer program thatignores trees and other ground cover. A topographic map or an orthophoto iscreated without the use of ground control. Precision is reported to be as fine as10 cm (DeLoach and Leonard, 2000; Gillbeaut, 2003).12 Geotechnical Investigation MethodsFIGURE 1.5False-color satellite image of northern New Jersey (ERTS-1, 1972). (From EROS Data Center, 1972.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 12Exploration 13FIGURE 1.6SLAR image of northern New Jersey. (Courtesy of USGS, 1984.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 13Airborne Imagery (Aerial Photography)● High-altitude stereo-aerial photographs provide the smallest scale images for stereo-viewing, ranging in scale from 1:125,000 to 1:100,000, yielding substantial detailon terrain features (Figure 1.7). Worldwide coverage, including the United States,is spotty.● Stereo pairs of aerial photographs provide the basis for detailed engineering geologicmapping. They can be obtained in panchromatic, true color, or color infrared(CIR). Single photos in true color and CIR are given in Figure 1.8. Detailed stud-ies of large to small areas should be based on stereoscopic interpretation. Becauseaerial photographs are the basis for modern topographic mapping they are avail-able on a worldwide basis, at least at scales of 1:50,000.Hyperspectral ImageryMultispectral scanners discussed above obtain images over a small number of broad spectralbands of the electromagnetic spectrum. They lack sufficient spectral resolution for precisesurface studies. Hyperspectral imaging (imagery spectrometry) has been developed in recentyears to acquire spectral data over hundreds of narrow, descrete, contiguous spectral bands.Various systems include SIS, AIS, AVIRIS, HIRIS and HYDICE, and others. Some are carriedby satellite (HIRIS), while others, such as AVIRIS (Airborne Visible/Infrared ImagingSpectrometer), are flown on aircraft platforms at heights of up to 100 km above sea level.The main objective of AVIRIS is to identify, measure, and monitor constituents of theEarth’s surface based on molecular absorption and particle scattering signatures. Someapplications include mineral identification for the mining industry for new sites and formine waste studies (Henderson III, 2000).14 Geotechnical Investigation MethodsSheet wash ofBajadasCatalina Mts.Fine-grainedvalley soilsFanSanta Cruz washFIGURE 1.7NASA high-altitude stereo-pair of an area northwest of Tucson, Arizona (scale 1:125,000). Apparent are sheetwash and sheet erosion of the “bajadas” alluvial fans of granular soils, valley fill of fine-grained soils, andthe “dry wash” of the Santa Cruz River, all typical depositional forms in valleys adjacent to mountains inarid to semiarid climates. (Original image by NASA reproduction by US Geological Survey. EROS DataCenter.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 14Seaborne Imagery● Side-scan sonar provides images of the seafloor or other water bodies, which oftenhave features indicative of significant geologic conditions. The images given asFigure 1.9 were obtained for a landslide study where the failure surface passedExploration 15FIGURE 1.8Aerial photos of a bridge abutment illustrating the advantage of infrared over true color. On the left isvegetation growing over shallow, poor-draining marine shales. On the right are relatively free-draininggranular glacial soils with sparce vegetation. (a) True color photo; (b) color infrared photo (CIR). (Courtesy of Woodward–Clyde Consultants.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 15into a reservoir. Figure 1.9a is a mosaic of a number of passes where water is 180ft deep. Figure 1.9b is a portion of one image showing the escarpment or tensioncrack along the reservoir margin. These images usually are obtained on a project-based need.1.2.4 Terrain AnalysisGeneralSignificanceTerrain analysis is often the most important part of any geotechnical investigation.Landforms (topographic expression) and other surface characteristics are strong indicators16 Geotechnical Investigation MethodsFIGURE 1.9Side-scan sonar images of a reservoir bottom. (a) Side-scan sonar mosaic of reservoir bottom, waterdepth � 180 ft; (b) detailed side-scan sonar image. A portion of the mosaic in (a). (Courtesy ofWoodward–Clyde Consultants.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 16of geologic conditions. Characteristic terrain features reveal rock type and structuralforms, where the rock is relatively shallow and subject to weathering and erosion, or rep-resent typical soil formations in terms of their origin and mode of deposition wheredeposits are sufficiently thick.ObjectivesThe delineation and mapping of the significant aspects of the geologic environment arethe objectives of terrain analysis. Information is provided on rock types and structures, soiltypes and formations, groundwater conditions, and floodplains; and, on the locations ofsuch hazards as landslides and other slope failures, sinkholes, and other instances ofground collapse and subsidence.MethodologyTerrain analysis is based on the interpretation of features evident on topographic mapsand remotely sensed imagery. Imagery interpretation as applied to engineering geologicmapping is summarized in Table 1.3, and as applied to environmental and naturalresource studies in Table 1.4. The elements of imagery interpretation are summarized inTables 1.5 and 1.6. Figures of USGS quadrangle sheets and stereo-pairs of aerial photosincluded in this book are summarized in Appendix B.Topographic maps, such as USGS quadrangle sheets, show landforms, drainage pat-terns, stream shape, and surface water conditions, all indicators of geologic conditions.Because of their availability and usefulness they should be procured as a first step inalmost any study.There are many forms of remote-sensing imagery presenting the features evident on the topographic maps. They are useful for environmental as well as geological studies. Exploration 17TABLE 1.3Uses of Remote Sensing for Engineering Geologic MappingInformation Desired Applicable ImageryRegional geologic mapping and delineation of major structural features Satellite and SLAR imagery(a) Global coverage, moderate resolution (a) LANDSAT(b) High resolution, but incomplete global coverage (b) SPOT, IKONOS, etc.(c) Useful for areas of perennial cloud cover and heavy (c) SLARvegetation; low resolutionDetailed mapping of rock type, structure, soil formations, Stereo-pairs of aerial photos drainage, groundwater, slope failures, sinkholes, etc. B&W, true color, CIR(a) Moderately large areas (a) Scale 1:100,000(b) Large areas, general mapping (b) Scale 1:60,000–1:40,000(c) Small areas, detailed mapping (c) Scale 1:20,000–1:8,000Improved definition of surface and groundwater conditionson Stereo-pairs of color infrared (CIR)large- to local- area basis, such as land–water interface, seepage, ground moisture (important for sinkhole and fault identification)Seafloor and other underwater conditions (rock outcrops, soils, Side-scan sonarsunken vessels, pipelines, etc.)Notes: (1) Normal studies of large land areas, such as for highways, airports, industrial zones, new communi-ties should be based on the interpretation of aerial photos of at least two scale ranges (1:60,000–1:40,000and 1:20,000–1:8,000).(2) Studies of areas where seismicity is of concern should always begin with interpretations ofERTS/LAND-SAT imagery, then be supplemented by interpretation of normal study imagery scales.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 17The selection of imagery depends upon availability, the study purpose, and the land areainvolved. Stereoscopic examination and interpretation of aerial photographs is the basicanalytical method.Remote-Sensing Imagery and InterpretationRegional Geologic StudiesOn a regional basis, landform is the most important element of interpretation for geotech-nical studies. In general terms, landform reflects the relative resistance of geologic materi-als to erosion. Some relationships among landform, rock type, and structure are apparenton the portion of the physiographic diagram of northern New Jersey in Figure 1.10. Thegeology of the area is shown in Figure 1.2. Landform is also evident in Figure 1.5, a false-color satellite image, and in Figure 1.6, a SLAR image.Millions of years ago the area illustrated in the figures was a peneplain. Modern phys-iography is the result of differential erosion between strong and weak rocks. Much of thearea has been subject to glaciation, and the limit of glaciation (the terminal moraine) is givenon the Geologic Map. The ridges and uplands, apparent on the physiographic diagram andthe figures, are underlain by hard rocks resistant to erosion, such as the conglomerate of theDelaware River Water Gap, the crystalline rocks of the Reading Prong (primarily gneiss),and the basalt dikes of the Watchung Mountains. Also apparent is the scarp of the RamapoFault, along the contact of the upland gneiss and the Triassic sandstones and shales. Thefolded sedimentary rocks in the northwest portion of the figures include the conglomerateridge, but are mostly relatively soft shales, and soluble dolomites and limestones. The shalesand soluble rocks are much less resistant to erosion than the conglomerate, gneiss, andbasalt. They erode more quickly and, therefore, underlie the valleys. The Great Valley ismostly underlain by the soluble rocks, i.e., dolomite and limestone. Farther to the northwestare the essentially horizontal beds of sandstones and shales of the Pocono Mountains. Theirapparently irregular surface has been gouged by the glacier.Satellite imagery is most important for terrain analysis where detailed geologic mapsare generally not available, such as in parts of Africa, Asia, and South America. Digitalsensors may not provide adequate coverage for areas with frequent cloud cover; radar,which penetrates clouds, is an option.18 Geotechnical Investigation MethodsTABLE 1.4Uses of Remote Sensing for Environmental and Natural Resource StudiesInformation Desired Applicable ImageryRegional environmental studies of air, water and vegetation Satellite imageryquality, flooding(a) On a changing or seasonal basis (a) LANDSAT(b) High resolution but incomplete global coverage (b) SPOT, IKONOS, etc.Surface and groundwater studies (large to local areas) CIR and Satellite (MSS) imagery(a) General (a) CIR and MSS imagery(b) Thermal gradients indicative of pollution or saltwater (b) Thermal IR scanner (ETM)intrusion of surface water(c) Subsurface seepage (c) Thermal scanner (ETM)Vegetation: forestry and crop studies (large to local areas) identify types, CIR and Satellite (MSS) imagerydifferentiate healthy from diseased vegetationMineral resource studies MSS and hyperspectral imagery(a) Based on landform analysis(b) Based on plant indicatorsCRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 18Exploration 19TABLE 1.5Elements of Imagery InterpretationImagery Feature Imagery Type InterpretationTopography Satellite images; SLAR: ● Rock masses as formed or subsequently stereo-pairs of aerial deformed have characteristic landphotos and topographic forms as do soil formationsmaps classified by mode of deposition or occurrence, which in allcases depend strongly on climate● Slope inclinations and heights are related to material types in terms of strength and structure● Slope failures, sinkholes, erosion gullies, etc. havecharacteristic formsDrainage patterns Satellite images; SLAR: ● Drainage patterns on a regional and and stream forms stereo-pairs of aerial local bases reflect rock type andphotos and topographic variations, rock structure, and wheremaps soil cover adequately thick, the soil type ● Stream form is also related to its geologic environment ● Streams, lakes, and swamps are indicators of the groundwater table, which usually follows the surface at depressed contours Gully Stereo-pairs of aerial Various soil types have characteristiccharacteristics photos (large scale) gulley shapes Photo tone B&W aerial photos Tone shows relative ground moisture and texture. Somegeneral relationships are● White — concrete, or free-draining soils above the water table ● Light gray — primarily coarse soils with some fines; acid rocks● Dull gray — slow-draining soils; basic rocksDark gray to black — poor draining soils, organic soils groundwater near the surfaceVegetation B&W aerial photos Vegetation varies with climate, geologic material, and land useTree lines often delineate floodplain limits and fault tracesLand use B&W aerial photos Most significant are the locations of man-made fills, cut for roadways, borrow pits, open-pit mines, and other man-made features. Development is usually related to landformColor-enhanced Satellite images Filtered through red: color significance(false-color) Red normally used for ● Vegetation — the brighter the red the imagery near infrared. Can be healthier is the vegetationpresented in various ● Water bodies — water absorbs sun’s colors to enhance rays, clear water shows black. Silt specific features reflects sun’s rays, sedimentation shows light blue● Urban areas — bluish-gray huesMultispectral photos or Various filters are used to emphasize the color IR desired feature (vegetation type, water-body pollution,thickness of snow field, etc.)Thermal IR Various filters are used to emphasize a particular feature.Can delineate water gradients to 1°FNote: In all color-enhanced imagery, ground truth is required to identify the feature related to a specific color.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 1920 Geotechnical Investigation Methods7766554321 7FIGURE 1.10Physiographic diagram of northern New Jersey illustrating relationships between rock type, structure, andlandform. 1, horizontally bedded sedimentary rocks; 2, folded sedimentary rocks; 3, batholith of recambriangneiss; 4, graben formed by fault blocks; 5, scrap of the Ramapo fault; 6, basalt dikes and diabase sill; 7,glacial lake beds. See also Geology Map (Figure 1.2), satellite image (Figure 1.5), and SLAR image (Figure1.6). (Figure drawn by E.J. Raisz, courtesy of Geographical Press, a division of Hammond World Atlas Corp.12643.)TABLE 1.6Interpretation of Color Infrared Photos (CIR)Color InterpretationRed Healthy vegetationBright Pasture, winter wheatDarker Evergreens: pine, conifersDark CypressPink Damaged or stressed vegetationLight Dead or unhealthy vegetationLight blue green Dead or unhealthy vegetationBluish-gray Dormant vegetationDark green-black WetlandsGreenish white Fallow fieldsWhite Bare fields, dry soilSandy beaches, gravel roads, snowGray Bare fields, wetsoil; urban areasBlue Water bodies; lakes, rivers; land fillsLight Heavy sediment loadBlue Moderate sediment loadDark Very little sediment loadBlack Clear water; or sedimentCRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 20Environmental StudiesAn important advantage of satellite imagery is the recording of changing conditions withtime for a given area, such as deforestation, detection of degradation of vegetation frompollution or other causes, and the extent of river-basin flooding.Some applications for water bodies as shown by color variations include: varying waterdepths in shallow water, different concentrations of sediment at mouths of rivers, andthermal gradients indicative of pollution or saltwater intrusion.Aerial PhotographsStereoscopic examination of stereo-pairs of aerial photographs is an extremely useful methodin the determination of geologic conditions. For large areas it is preferable to obtain photos attwo scale ranges 1:60,000 to 1:40,000 (Figure 1.11) and 1:20,000 to 1:8,000 (Figure 1.12), withthe smaller scales providing an overview and the larger scales providing details. A stereo-pairExploration 21Slump slide scarsFIGURE 1.11Stereo-pair of serial photos (scale 1:40,000) shows landform developing in metamorphic rocks from subtropicalweathering. Severe erosion and a number of landslides are apparent, including the rotational slides shown onthe larger scales as in Figure 1.12.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 21at a scale of 1:40,000 is given in Figure 1.11. It shows the landform developing in metamor-phic rocks from subtropical weathering. Slump slide scars are observed on the photos. Figure1.12 is a stereo-pair at a scale of 1:8,000 of a portion of the area in Figure 1.11. A geologist inter-preting stereo-pairs with a stereoscope is shown in Figure 1.13.The elements of imagery interpretation are summarized in Table 1.5. CIR (Figure 1.8)depicts landscapes in colors very different from those in true color photos. Healthyvegetation, for example, appears in shades ranging from bright pink to deep-reddishbrown. Table 1.6 lists different colors of some typical surface materials as shown in CIRphotographs.Samples of stereo-pairs of aerial photographs included in this book are summarized inAppendix B. Techniques of terrain analysis and air photo interpretation are described byWay (1978), Lueder (1959), ASP (1960), Belcher (1948), and Avery and Berlin (1992), amongothers.22 Geotechnical Investigation MethodsFIGURE 1.12Stereo-pair of aerial photos (scale 1:8,000) of a portion of Figure 1.11 provides substantially more detailedinformation on the soil conditions and their distribution. The spoon-shaped slide that occurred in residual soilsis clearly apparent. Its rounded forms, resulting from erosion, indicate that the slide is relatively old.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 22Interpretive Features of Topographic MapsTopographic maps, such as the USGS Quadrangle sheets, provide the simplest and leastcostly data for terrain analysis. Scales of 1:50,000 to 1:250,000 show regional landforms anddrainage patterns and can indicate rock type and regional structural features such as foldsand lineations, the latter often representing faults. Older maps often show the locations ofmines. Scales of 1:10,000 to 1:24,000 provide more local detail on features such as slopes,soil formations, and sinkholes.Interpretation of geologic conditions is based primarily on landforms as disclosed bycontour lines and drainage patterns. A list of the USGS quad sheets included in this bookare given in Appendix B. They illustrate many relationships between landform and geology.The topographic map (Figure 1.3) illustrates the relationship between landforms as disclosed by contour lines and geologic conditions. Landforms reflect the differential resist-ance to erosion of the various rock types, as shown on the 3-D diagram inset in Figure 1.3.The area has been glaciated and is underlain with hard granitic gneiss and relatively weakshales, and soluble dolomite and limestone in the valleys. The closely spaced contours inFigure 1.3 in the gneiss indicate the steep slopes characteristic of hard rock. The marshylands and the Wallkill River are indicative of the groundwater table in the valleys; themarshy area in the gneiss uplands, high above the river, indicate a perched watertable con-dition. Topographic maps are very useful in estimating groundwater conditions, althoughseasonal variations must be considered.The landforms evident in Figure 1.14, a copy of the USGS Quad of Wallingford,Connecticut, are indicative of several geologic formations; the steep-sloped, irregularlyshaped form in the upper left is an area of very resistant granite gneiss at shallow depths.Exploration 23FIGURE 1.13Stereoscopic interpretation of aerial photographs. Two types of stereo-viewers are shown.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 23The Quinnipiac River is in its middle stage or floodway zone, flowing over the remnantsof a glacial lake bed and depositing fine-grained soils during flood stages (recent allu-vium). The very flat areas, generally between the railroad and the river extendingthrough the middle portion of the map to about Elev 50, constitute a sand and gravel ter-race formation, which at one time was the valley floor. A gravel pit is noted in the terraceformation, and areas of poor drainage (swamps and ponds) are apparent in the right-hand portion of the map, along Pond Hill Road. These perched water conditions abovethe valley floor result from the poor internal drainage of the underlying clayey glacial till.Engineering Geology MapsGeneralData obtained from terrain analysis can be plotted to prepare an engineering geology map that provides information on geologic conditions over an entire study area. 24 Geotechnical Investigation MethodsFIGURE 1.14USGS quadrangle map, Wallington, Connecticut (scale 1:24, 000). Map provides detailed information on terrainfeatures. (Courtesy of USGS.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 24When interpreted with experience, significant knowledge regarding the engineeringcharacteristics of the formations and materials becomes available.Preliminary map assessment permits conclusions regarding:1. Abandonment of the site to avoid extremely hazardous conditions2. Location of structures to avoid unfavorable conditions3. General requirements for foundations and excavation4. Formulation of the program of subsurface investigationMap PreparationUsing a topographic map as a base map, select a scale convenient to the study area andpurpose. Plot the data obtained from terrain analysis including boundaries of the varioussoil and rock types, major structural features, areas of shallow groundwater and rock, andlocations of hazards such as sinkholes and landslides. A suggested nomenclature for theidentification of various soil and rock formations is given in Table 1.7.Exploration 25TABLE 1.7Suggested Map Symbols for Engineering Geology MapsClassification Symbol Modifiers Based on Coarseness or OccurrenceResidual soil R Rm — massiveRs — saproliteRc — coarse-grained (granular)Rf — fine-grained (clayey or cohesive)Colluvial soil C Cr — originally residual soilCm — originally glacio-marine soilsCl — originally glacio-lacustrine soilsT — talusAlluvail soil A Ao — oxbow lakeAt — terraceAr — recent alluvium; usually silt–sand mixtures with organic matterAc — coarse grained; sand and gravel mixturesAm — medium grained; sand–silt mixturesAf — fine grained; silt–clay mixturesEolian soil E El — loessEd — dunesGlacial soils G Gm — moraineGt — tillGs — stratified drift (outwash plains)Gk — kaneGe — eskerGl — lakebedOrganic soils O Om — marshOs — swampMan-made fill FHigh watertable HgRock symbolsIgneous Sedimentary Metamorphicgr — granite sg — conglomerate qz — quartzitery — rhyolite ss — sandstone ma— marblesy — syenite si — siltstone hr — hornfeldmo — monzonite sh — shale gn — gneissdi — diorite ls — limestone sc — schistga — gabbro ak — arkose ph — phylliteba — basalt do — dolomite sl — slateCRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 25Preparation is first on a preliminary basis; a final map is prepared after site reconnais-sance and, preferably, after at least some subsurface investigation. To aid in reconnais-sance, all significant cuts and other surface exposures should be noted on the map, as wellas areas of questionable conditions.Assessment of Mapped ConditionsSoil formations: Soils may be geologically classified by their origin and mode of occurrence,the engineering significance of which lies in the characteristic properties common to the various classes. Therefore, if a soil formation is classed in terms of originand mode of occurrence, preliminary judgments can be made regarding their influence onconstruction.Rock formations: The various rock types have characteristic engineering properties andstructural features, either as originally formed or as deformed by tectonic or other geologicactivity. The identification of rock-mass features allows the formulation of preliminaryjudgments regarding their influence on construction.Three examples of engineering geology maps illustrate the approach:1. A proposed new community in a region of glacial soils is illustrated in Figure1.15. Conditions may be generally interpreted for engineering purposes solely onthe basis of the soil types, classified geologically as follows:(a) Foundation conditions: RX, GT — good support all loads; GK — good supportmoderate loads; GL, GT/GL-possible suitable support for light to moderate26 Geotechnical Investigation MethodsFIGURE 1.15Preliminary engineering geology map of Bromont, Quebec, Canada. Conditions may be generally interpretedfor engineering evaluations as described in the text. (Courtesy of Joseph S. Ward and Assoc.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 26loads; AF-probable poor support. Areas of GK, GL, GT/GL, and AR in par-ticular require detailed investigation. (NOTE: Terms such as “moderateloads” or “poor support” require definition in the report accompanying themap.)(b) Excavation conditions: RX areas will require blasting. High groundwater canbe expected in areas of AF and GL.(c) Borrow materials: Coarse-grained granular soils are found in GK.(d) Septic tanks: High groundwater, clayey soils, or shallow rock over much ofthe area imposes substantial constraint to their use.(e) Groundwater for potable water supply: Most feasible locations for wells are atthe base of slopes in the GT and GK materials. Buried channel aquifers mayexist in the valley under the GL deposits.2. An interstate highway planned for an area with potential slope stability prob-lems is illustrated in Figure 1.16; slope failures in the area are shown on thestereo-pair (Figure 1.17). The area is characteristic of many glaciated valleys inthe northeast United States, which were once the locations of glacial lakes.3. A community to receive a new sanitary sewer system is illustrated in Figure 1.18a.An aerial photo of the area is given in Figure 1.18b and stereo-pairs in Figure 1.19.Exploration 27Al: recent alluvium Gl: ancient lakebed soilsAt −Gl: lacustrine terrace rx: rock under thin GmFIGURE 1.16General engineering geology map prepared for interstate highway through a valley with glacial lacustrine soils onthe slopes (Barton River Valley, Orleans, Vermont). The lower slopes in the At-GL material are subjected to activemovements (see stereo-pair, Figure 1.17); the upper slopes in overconsolidated GL soils (stiff to hard varved clays)will tend to be unstable in cut. In many areas, the Al soils will be highly compressible under embankment fills.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 2728 Geotechnical Investigation MethodsFIGURE 1.17Stereo-pair of aerial photos showing old slide scars in glacial lakebed terrace soils (Barton River Valley,Orleans, Vermont). FIGURE 1.18 (A)Preliminary engineering geology map. Sanitary sewer study, West Nyack, New York. Note: GT�glacial till;Ss�Sandstone; GT/Ss � 10’ GT over Ss; GT/Db � 10’ GT over diabase; AL�recent alluvium (lakebed soils);Z/AL�organic soils over alluvium. (Courtesy of Joseph S. Ward and Assoc.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 28The conditions shown on the preliminary map were investigated with seismicrefraction surveys and a few test borings and pits. For sanitary sewer studies, themajor concerns are depth of rock and groundwater as they affect excavations, andfoundation problems caused by weak soils such as organics and lakebed soils. Thelarge cuts along the highways expose conditions and serve as very large test pits.A rock cut in sandstones is indicated as A, and a soil cut in glacial till is indicatedas B on the stereo-pairs of Figure 1.19.Other map forms prepared for engineering studies can include:1. Geologic hazard, or risk maps, which delineate geologic conditions in terms of var-ious degrees of hazard or risk such as terrain where soil liquefaction or slopefailures are of concern.. 2. Geologic constraint maps form the basis for the preparation of land-use maps.1.2.5 Site ReconnaissanceGeneralAll sites should be visited by an experienced professional to collect firsthand information ongeology, terrain and exploration equipment access, existing structures and their condition,existing utilities, and potentially hazardous conditions. Prior examination of aerial photoswill identify many of the points to be examined.Exploration 29FIGURE 1.18(B)Aerial photo of West Nyack area. Soil cut at (B); rock cut at (A).CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 2930 Geotechnical Investigation MethodsFIGURE 1.19Stereo-pairs of aerial photos, West Nyack, New York. (A) Rock cut, sandstones; (B) soil cut, glacial till.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 30Reconnaissance Checklist1. Examine exposures of soils and rocks in cuts (highways, rail-roads, buildingexcavations, gravel pits, quarries, stream banks, and terraces), and on the sur-face, and note effluent groundwater seepage.2. Examine slopes for signs of instability (creep ridges, tilted and bent trees, tiltedpoles, and slope seepage).3. Examine existing structures and pavements for signs of distress.4. Note evidence of flood levels along streams.5. Contact local architects and engineers for information on foundations and localsoil conditions.6. Contact local well drillers for information on groundwater conditions.7. Contact local public officials for building code data and information on founda-tions, soil conditions, and on-site utilities.8. Note site conditions imposing constraints on access for exploration equipment.9. Note present land use.Revise Engineering Geology MapThe information gathered during site reconnaissance is used to revise the preliminaryengineering geology map where necessary.1.2.6 Preparation of Subsurface Exploration ProgramPrepare the subsurface exploration program, considering the necessity of:● Confirming the boundaries of the various geologic formations as mapped.● Obtaining data for the preparation of geologic sections.● Obtaining samples for identification, classification, and laboratory testing.● Obtaining in situ measurements of the engineering properties of the materials.1.3 Subsurface Exploration1.3.1 GeneralObjectives● To confirm or supplement the engineering geology map showing shallow andsurficial distributions of the various formations.● To determine the subsurface distribution of the geologic materials and ground-water conditions.● To obtain samples of the geologic materials for identification and laboratory test-ing (Section 1.4).● To obtain in situ measurements of engineering properties(Chapter 2).Exploration Method CategoriesGeneral Categories● Direct methods allow the examination of materials, usually with the recovery ofsamples; examples are excavations and test borings.Exploration 31CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 31● Indirect methods provide a measure of material properties; examples are geo-physical methods and the use of the cone penetrometer, which through correla-tions allow an estimation of material type.Specific Categories● Geophysical methods provide indirect data (Section 1.3.2).● Reconnaissance methods provide direct and indirect data (Section 1.3.3).● Continuous cone penetrometer (CPT) (Section 1.3.4).● Test and core borings provide direct data (Section 1.3.5).● Remote borehole sensing and logging provide direct and indirect data (Section 1.3.6).Method SelectionBasic FactorsSelection is based on consideration of the study objectives and phase, the size of the studyarea, project type and design elements, geologic conditions, surface conditions and acces-sibility, and the limitations of budget and time.The various methods in terms of their applicability to general geologic conditions arelisted in Table 1.1.Key MethodsGeophysical methods, particularly seismic refraction surveys, provide the quickest and oftenthe most economical method of obtaining general information over large land areas, or inareas with difficult access, such as mountainous regions or large water bodies. They areparticularly useful in investigating shallow rock conditions.Test pits and trenches are rapid and economical reconnaissance methods for obtaininginformation on shallow soil, groundwater conditions, and depth and rippability of rock,and for investigating landfills of miscellaneous materials.Test borings are necessary in almost all investigations for the procurement of soil androck samples below depths reachable by test pits.Other methods can be generally considered to provide information supplemental to thatobtained by key methods.1.3.2 Geophysical methodsThe more common geophysical methods are summarized in Table 1.8.Seismic Methods: GeneralTheoretical BasisElastic waves, initiated by some energy source, travel through geologic media at character-istic velocities and are refracted and reflected by material changes or travel directlythrough the material, finally arriving at the surface where they are detected and recordedby instruments (Figure 1.20). There are several types of elastic waves.Compression or primary (P) waves are body waves that may propagate along the surfaceand into the subsurface, returning to the surface by reflection and refraction, or that maytravel through the materials as direct waves. P waves have the highest velocities Vp andarrive first at the recording instrument.Shear (S) waves are also body waves propagating and traveling in a manner similar to Pwaves. S waves travel at velocities Vs, from approximately 0.58Vp for well-consolidated32 Geotechnical Investigation MethodsCRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 32Exploration 33TABLE 1.8Geophysical Methods of Exploration SummarizedMethodApplicationsCommentsSeismic refraction from surfaceObtain stratum depths and velocities, land Most suitable if velocities increase with or water. Geologic sections interpreteddepth and rock surface regularSeismic direct (crosshole, uphole, Obtain velocities for particular strata; Requires drill holes. Crosshole yields best downhole)dynamic properties; rock mass qualityresults. CostlySeismic reflectionGeneral subsurface section depicted. Land results difficult to interpret. Water bodies yield clearest sectionsVelocities not obtained. Stratum depths comps require other dataElectrical resistivityLocate saltwater boundaries, clean Difficult to interpret. Subject to wide granular and clay strata, rock depth, andvariations. No engineering propertiesunderground mines by measured obtained. Probe configurations varyanomaliesElectrical conductivityObtain subsurface sections by data Difficult to interpret. Subject to wide interpretation. Identify contaminant variations. No engineering properties plumes by measured anomaliesobtainedGravimeterDetect faults, domes, intrusions, cavities, Precise surface elevations needed. Not buried valleys by measured anomaliescommonly used. Measures densitydifferencesMagnetometerMineral prospecting, location of large Normally not used in engineering or igneous massesgroundwater studiesGround-probing radarGeneral subsurface section depicted. Most useful to show buried pipe, bedrock, Interpretation difficult. Limited to shallow voids bouldersdepths. No engineering propertiesThermographyShallow subsurface section depicted. Interpretation difficult. Limited to shallow Useful for water pipeline leaksdepths. No engineering propertiesCRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 33materials to 0.45Vp for poorly consolidated soils. They are not transmitted through wateror across air gaps.Rayleigh (R) waves propagate only near the surface as a disturbance whose amplitudeattenuates rapidly with depth, traveling at a velocity approximately 0.9Vp. The recordedvelocity may be less because R waves travel near the surface where lower-velocity mate-rial normally occurs, and usually consist of a trail of low-frequency waves spread out overa long time interval.Transmission CharacteristicsIn a given material, the arrival time of each wave at the recording instrument depends onthe travel distance between the energy source and the detector, which is in turn a functionof the depth of the stratum. In a sequence of strata with successively higher velocities,there is a distance between the energy source and the detector at which the refracted waveis transmitted through a higher velocity material and arrives at the detector before thedirect or reflected wave. Even though the direct and reflected waves travel shorter dis-tances, they are transmitted at lower velocities.For land explorations to depths of less than about 1000 ft (300 m), seismic refractiontechniques traditionally have been used rather than reflection because the direct andrefracted waves arrive first and tend to mask the reflected waves. Reflection seismology is34 Geotechnical Investigation MethodsHammer blowenergy sourceDirect wave path DetectorReflected wave pathRefracted wave pathReflective distanceSecond reflection pathSecond refraction pathV2V2V1V3(a)(b)(c)V1dFIGURE 1.20Transmission paths of (a) direct, (b) reflected, and (c) refracted seismicwaves through shallow subsurface.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page34normally used for deep exploration and for marine studies for profiling, but does notdirectly yield velocity data as do refraction and direct techniques.Seismic Exploration TechniquesRefraction techniques are used to measure compression (P) wave velocities in each geologic stra-tum, which are indicative of type of material and location of the groundwater table, to esti-mate the depths of various substrata, and to indicate the locations of faults and large caverns.Direct techniques provide information on rock-mass characteristics, such as fracture den-sity and degree of decomposition, and on dynamic soil and rock properties including Young’smodulus, Poisson’s ratio, shear modulus, and bulk modulus (Sections 2.5.3 and 2.5.5).Reflection techniques have been used primarily in marine investigations. They provide apictorial record of the sea-bottom profile showing changes in strata, salt domes, faults, andmarine slides. Since velocities are not directly measured, material types and depths of stratacan only be or cannot be inferred unless inferred when correlations are made with other data.Energy Sources for Wave PropagationImpact source (hammer or weight drop), used for shallow explorations on land, tends togenerate disproportionately large Rayleigh surface waves, but also produces large Pwaves, helpful for engineering studies. Explosives, used for land and subaqueous studies,convert a smaller portion of their energy into surface waves, especially when placed atsubstantial depths below the surface. High-energy spark is used for subaqueous studies. Seealso Griffiths and King (1969) and Mooney (1973).Seismic Refraction MethodGeneralSeismic refraction techniques are used to measure material velocities, from which depths ofchanges in strata are computed. Material types are judged from correlations with velocities.Basic equipment includes an energy source (hammer or explosives); elastic-wave detec-tors (seismometers), which are geophones (electromechanical transducers) for land explo-ration or hydrophones (pressure-sensitive transducers) for aqueous exploration; and arecording seismograph that contains a power source, amplifiers, timing devices, and arecorder. Equipment may provide single or multiple-recording channels. The recorded elastic waveforms are presented as seismograms.Operational ProceduresSingle-channel seismograph operation employs a single geophone set into the ground, ashort distance from the instrument. A metal plate, located on the ground about 10 ft (3 m)from the instrument, is struck with a sledge hammer (Figure 1.21). The instant of impactis recorded through a wire connecting the hammer with the instrument. The shock wavestravel through the soil media and their arrival times are recorded as seismograms or asdigital readouts. The plate is placed alternately at intervals of about 10 ft (3 m) from thegeophone and struck at each location with the hammer. Single-channel units are used forshallow exploration under simple geologic conditions.Multi-channel seismographs employ 6 to 24 or more geophones set out in an array to detectthe seismic waves, which are transmitted and recorded simultaneously and continuously.The older seismographs recorded data on photographic film or magnetic tape; and modernseismographs record digital data in discrete time units. The energy source is usually someform of an explosive charge set on the surface or in an auger hole at a shallow depth. Thedesired depth of energy penetration is a function of the spread length (distance between theExploration 35CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 35shot point and the farthest geophone), which should be, in general, 3 to 4 times the desiredpenetration depth. A normal spread would be about 300 ft (100 m) to investigate depths to100 ft (30 m) with geophones spaced at 30 ft (10 m) intervals to define the velocity curves.The geophysicist determines the spread length and the geophone spacing to suit the antic-ipated geological conditions. In practice, a shot is usually set off at one end of the spread,and then another at the opposite end (reverse profiling) to detect stratum changes and slop-ing rock surfaces. At times, charges are set off in the middle of the spread or at other loca-tions. Multi-channel units are used for deep exploration and all geologic conditions.SeismogramsSeismic waveforms are usually recorded on photographic paper as seismograms. InFigure 1.22, the P wave, traveling at the highest velocity, is the first arrival to be recordedand is easily recognized. It is used to determine the depths to the various strata on thebasis of their characteristic transmission velocities.The S wave appears later in the wave train as a large pulse and is often difficult to recog-nize. In the figure, it is observed crossing the spread at an intermediate angle from the firstarrivals, indicating a lower velocity. S wave velocities are used in conjunction with P wavevelocities to compute the dynamic properties of the transmitting media (Section 2.5.3).36 Geotechnical Investigation MethodsFIGURE 1.21Single-channel refraction seismograph. Man in upper right with hammer striking metal plate causes seismicwaves.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 36The Rayleigh wave (R) appears as a large-amplitude, low-frequency signal arriving lateon the train. In the figure, it crosses the spread at an angle larger than the S wave andleaves a record at about the 200 ft spread. Although easy to recognize, the beginning isessentially indeterminate and does not provide much information for engineering studies.Time–Distance Charts and AnalysisA typical time–distance chart of the first arrivals obtained with a single-unit seismographis given in Figure 1.23. As the distance from the geophone to the shot point is increased,eventually the shock waves will have sufficient time to reach the interface between mediaof lower and higher velocities, to be refracted and travel along the interface at the highervelocity, and to arrive before the direct and reflected waves traveling through the shal-lower, lower-velocity material.The travel times of the first arrivals are plotted against the distance from the geophoneand the velocity of the various media determined from the slopes of the lines connectingthe plotted points as shown in the figure.Exploration 37Distance from recording station, geophones at 25-ft intervals30027525022520017515012510075PS RFirstarrival50252.5 ms per divisionFIGURE 1.22Seismograms of waveforms recorded at 25-ftintervals as caused by 300-lb weight drop.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 37Various formulas are available for computing the depth of the interfaces of the variouslayers, varying from simple to complex depending on the number of layers involved andthe dip of the beds. The formulas for computing the depths of the relatively simple three-layer problem are given in Figure 1.23 (see equations (1.1) and (1.2)). For interpretationsome information on topography must be available.Actual seismograms for three shots along the same spread (each end and the middle)are given in Figure 1.24, and the time–distance plots in Figure 1.25. The example, a three-layer problem in a residual soil profile, is from a continuous profiling study for a railroad.The resulting subsurface section is given in Figure 1.26.Limitations● Softer, lower-velocity material will be masked by overlying denser, higher-velocity material and cannot be directly disclosed.● A stratum with a thickness of less than about one fourth the depth from theground surface to the top of the stratum cannot be distinguished.● Erratic or “average” results are obtained in boulder formations, areas of irregu-lar bedrock surfaces, or rock with thin, hard layers dipping in softer rock.● Well-defined stratum interfaces are not obtained where velocityincreases grad-ually with depth, as in residual soil grading to weathered to sound rock.38 Geotechnical Investigation MethodsVelocity V = slope of lineV1 = 20 ft /15 ms = 1333 ft /sV2 = 20 ft /25-20 ms = 4000 ft /sV3 = 20 ft /29-27 ms = 10,000 ft /sXc = Critical distance from intersection of lines V1, V2, and V3V2V1First arrivals40302010010 20 30 40 50 60 70 80Travel time (ms)Distance from geophone (ft)SeismographGeophoneDry sand GWL d1ShotpointFind depths, d1, and d2Shown are presumed paths of first waves to geophoneSaturated sandd1 = √Xc1 V2 − V1V2 + V12Xc2 = 56 ftXc1 = 24 ftdf = 8.5 ftd2 = 25.4 f tXc22+d2 = (1.1)(1.2)V3 − V2V3 + V20.8 d1√V3d2FIGURE 1.23Time–distance graph and the solution to a three-layer problem.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 38Exploration 39Right end shotgeophones(+000)(+000)(+000) 50 10050 10050 100232221201918171615141312111098765432124232221201918171615141312111098765432TA1TimebreakCenter shotgeophonesTimebreak242322212019181716151413121110987654321Left end shotgeophonesTimebreak10 msFirst arrivalsFIGURE 1.24Seismograms for one 24-channelspread with three shot points.(Courtesy of Technosolo.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 39● In frozen ground, the shot point and geophones must be below the frozen zonebecause the shock waves travel much faster through frost than through theunderlying layers.● Application in urban areas is limited because of utility lines, pavements, foun-dations, and extraneous noise sources.ApplicationsThe method is most suitable as an exploration tool where there are media with den-sities that increase distinctly with depth, and fairly planar interface surfaces. In suchinstances, it can economically and efficiently provide a general profile of geologic condi-tions (Figure 1.26).Material types are estimated from computed P wave velocities. Typical velocities formany types of materials are given in Table 1.9, and for weathered and fractured igneousand metamorphic rocks in Table 1.10.Velocity data are also used to estimate rock rippability (see Table 2.7).Seismic Direct MethodsApplicationsSeismic direct methods are used to obtain data on the dynamic properties of rocks andsoils (Chapter 2), and to evaluate rock-mass quality. See also Auld (1977), Ballard Jr. (1976),and Dobecki (1979).Techniques (Figure 1.27)Uphole survey: The geophones are laid out on the surface in an array, and the energy sourceis set off in an uncased mud-filled borehole at successively decreasing depths starting atthe bottom of the hole. The energy source is usually either an explosive or a mechanicalpulse instrument composed of a stationary part and a hammer.40 Geotechnical Investigation MethodsTime (ms)100t27520155458127514V0 = 200V1 = 1500Depth(m)1.5 3.2 28.3Depth(m)1.5 3.3 30.8Velocity(m/s)V0 = 300/400V1 = 900V2 = 5000Depth(m)1.5 3.2 22.1Depth(m)1.5 3.5 24.9Velocity(m/s)V0 = 350/400V1 = 1000V2 = 5000V2 = 6000Irregularly distributed points reflectchanges in topography or irregularity in depthV2 = 5500 V2 = 4500V2 = 4500V1 = 800V0 = 400 V0 = 400V0 = 350V1 = 1250V1 = 800t1t2t11001 2Left end shot Geophones, 10 - m stationing Center shotGeophone numbersRight end shot3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24FIGURE 1.25Time–distance graphs for the seismograms of Figure 1.24. (Courtesy of Technosolo.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 40Downshole survey: The energy source is located on the surface and the detectors incor-porated in a sonde which is raised or lowered in the borehole, to give either a continuousor intermittent log of adjacent materials.Crosshole survey: The energy source is located in a center test boring and the detectorsare placed at the same depth as the energy source in a number of surrounding boreholes.Advantages over Refraction SurveysIn the uphole and downhole methods, the influence of reflection and refraction from thelayers surrounding the layer of interest is substantially reduced.In the crosshole method, the influence of surrounding layers is eliminated (unless theyare dipping steeply) and the seismic velocities are measured directly for a particular stra-tum. Crosshole is the dominant and most useful technique.Seismic Reflection MethodApplicationSeismic reflection surveys obtain a schematic representation of the subsurface in terms oftime and, because of the very rapid accumulation of data over large areas are used in engi-neering studies, primarily offshore. In recent years, as technology has improved, themethod is being used with increasing frequency to pictorialize stratigraphy in land areas.The results for a landslide study are shown in Figure 1.28. The sliding mass was 3500 ft inlength and the survey was to identify wedge boundaries in the failure zone. For marine surveys, reflection methods are much more rapid than refraction surveys and,when obtained from a moving vessel, provide a continuous image of subseafloor conditions.Operational ProceduresContinuous marine profiling is usually performed with an electric–sonic energy source gen-erating continuous short-duration pulses, while towed behind a vessel, in conjunctionwith a hydrophone that detects the original pulses and reflected echo signals. The outputExploration 41Elevation (m)650BoringV0 = 300 m/sV1 = 1200 m/sV2 = 3000 m/sV3 = 5000 m/sLegend: V0 = Residual soil above groundwater level V1 = Residual soil below groundwater level V2 = Moderately weathered and fractured rock V3 = Fresh to slightly weathered rockV1 = 1200 m/sV2 = 2500 m/sV3 = 4500 m/sFinalroadwaygrade625600575500 510Station number520 530FIGURE 1.26Example of subsurface section prepared from a continuous refraction profile. Velocities are correlated withrippability as shown in Table 2.7.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 4142 Geotechnical Investigation MethodsTABLE 1.9Typical Compression-Wave Velocities in Soils and RocksVelocity (m/s) 1000 1 2 3 4 5 6 7(ft/s × 1000) 5 10 15 20 25MaterialSoils (above GWL)Topsoil, leached, porousLoessAlluvium: soft or looseColluvium: soft or looseAlluvium: firm to medium coarseColluvium: firm to medium coarseClaysGlacial till (compact)ResidualResidual (saprolite)WaterSedimentary RocksSandstone (soft to hard)Shale (soft to hard)LimestoneSoftHardCrystallineAnhydrite, gypsum, saltMetamorphic RocksSlateSchistGneissMarbleQuartziteIgneous RocksWeathered FracturedGraniteGranodioriteQuartz monzoniteGabbroDiabaseBasaltNotes: (1) Velocities given are for dry soil conditions. As the percent saturation increases so do velocities: there- fore, a velocity change may indicate the water table rather than a material change. (2) The wide range of velocities given for rocks reflect the degree of weathering and fracturing: sound, massive rock yields the highest velocities.} Also gneissof the hydrophone is amplified and passed to a recorder, which transcribes each sparkevent to sensitized paper, directly resulting in a pictorial section beneath the water surface.Equipment in use is generally of two types:● “Subbottom Profilers,” “Boomers,” and “Bubble Pulsers” provide penetrationdepths below the water-body floor in the range of 50 to 100 m. In general,Subbottom Profilers and Boomers provide higher resolution and Bubble Pulsersprovide deeper penetration. They are often used together.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 42● “Sparkers” and “airguns” provide penetrations to depths of 50 to 1000 m ormore. They generally operate in water depths from 10 to 600 m withresolutioncapabilities of about 15 to 25 m. Interpretive Information ObtainedA pictorial section beneath the seafloor, or other large water body, is obtained, showing thegeneral stratigraphy, and such features as slumps and gas pockets when the resolution ishigh. Figure 1.29 is a Bubble Pulser image below a reservoir bottom in about 100 ft ofwater. The study purpose was to locate possible rupture zones at the toe of a large land-slide. Figure 1.9 is a side-scan sonar image of the area.Deeper penetration methods, such as sparker surveys, can indicate major geologicstructures such as faults and salt domes (Figure 1.30) and massive submarine slides.Velocities cannot be calculated with reliability since distances are not accurately known,and therefore material types and stratum depths cannot be evaluated as in refractionExploration 43TABLE 1.10Typical P-Wave Velocities of Weathered and Fractured Igneous and Metamorphic RocksMaterial Grade Vp (m/sec)Fresh, sound rock F 5000�Slightly weathered or widely spaced fractures WS 5000–4000Moderately weathered or moderately close fractures WM 4000–3000Strongly weathered or close fractures WH 3000–2000Very strongly weathered (saprolite) or crushed WC 2000–1200aResidual soil (unstructured saprolite), strong RS 1200–600aResidual soil, weak, dry RS 600–300aa Vp (water) ≈ 1500 m/sec. Vp (min) of saturated soil ≈ 900 m/sec.Geophones on surfacefor uphole surveyRDownholeshotpointS - shothole R - recording holePartially reflected and refracted pathsGeophone: downholeor crossholeShot point for upholeor crossholeDirect wave pathGeophone forcrossholeor downholeFIGURE 1.27Direct seismic methods to measure dynamic properties of soils and rocks, and assess rock mass quality. A single borehole is used in the uphole or downhole survey; array of usually four borings is used in thecrosshole survey. In uphole surveys, the geophones should be set on rock. If possible, to obtain measurementsof rock quality.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 43methods. Depths are estimated by assuming a water velocity of 2500 m/sec, but variationsin strata impedance affect the thickness scale. Test borings or refraction studies are neces-sary for depth- and material-type determinations.Electrical Resistivity MethodsApplicationsThe resistivity of soil or rock is controlled primarily by pore water conditions that varywidely for any material. Therefore, resistivity values cannot be directly interpreted interms of soil type and lithology. Some applications are:● Differentiation between clean granular materials and clay layers for borrow-material location.● Measurement of the thickness of organic deposits in areas difficult to access.● Measurement of the depth to a potential failure surface in “quick” clays in whichthe salt content, and therefore the resistivity, is characteristically different nearthe potential failure surface.● Location of subsurface saltwater boundaries.● Identification of variations in groundwater quality in homogeneous granulardeposits, as may be caused by chemical wastes leaking from a storage basin.● Measurement of depth to bedrock and delineation of varying rock quality.● Location of solution cavities in limestone and underground mines (not alwayssuccessful).44 Geotechnical Investigation Methods160Surface elevationsGlacialoverburdenWeatheredtofracturedtosoundmarineshales150166016701680169017001710166016701680169017001710140 130 120 1102505075100150200300400500EASTFIGURE 1.28Seismic reflection profile for landslide study. Shown are interpreted slope failure surfaces. (Courtesy ofWoodword–Clyde Consultants.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 44Exploration 45Approximate depth in feet below lake level25020015010050North Line direction150 152 154 156Pier 12Recent river deposits158SouthHorizon B200 ftHorizon AMultiplesPossible fault /glide planeFormer Missouririver channelSide reflectionsfrom bridge piersPier 13Pier 14FIGURE 1.29Subbottom profiling with bubble pulser to locate possible failure surface at toe of landslide. Section is in areaof side-scan sonar image (see Figure 1.9). (Courtesy of Woodward–Clyde Consultants.)Seconds5.06.07.08.09.0Seconds5.06.07.08.09.0Salt10 km Fault? "Acoustic basement"Campecheescarpment SeafloorDSDP3,87 NW Seismic unitsSigsbeeCinco de MayoMexican ridgesCampecheChallengerDepth 10 km*SigsbeeCinco de MayoMexican ridgesCampecheChallengerViejo*Approximate depth computed from refraction profile dataNW?? ? ? ?SeafloorSE10 kmChallenger Knolisalt domeDSDP-2SEFIGURE 1.30Part of multichannel seismic reflection section, abyssal western Gulf of Mexico. (From Ladd, J. W. et al.,Geology, GSA, 1976. With permission.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 45Theoretical BasisVarious subsurface materials have characteristic conductances for direct currents of elec-tricity. Electrolytic action, made possible by the presence of moisture and dissolved saltswithin the soil and rock formations, permits the passage of current between electrodesplaced in the surface soils. In general, conductance is good in materials such as moist claysand silts, and poor in materials such as dry loose sands, gravels, and sound rocks.Resistivity refers to the resistance to current flow developed in geologic materials and isexpressed as Ω cm2/cm, or simply as Ω cm or Ω ft. Some typical values of resistivity forvarious geologic materials are given in Table 1.11.ApparatusThe electrical resistivity apparatus consists of a battery as energy source, a milliammeter,a potentiometer, and electrodes (Figure 1.31). There are three basic electrode configura-tions as shown in Figure 1.32.Wenner array: Commonly used in the United States, it employs four equally spaced elec-trodes. All four electrodes are moved between successive operations. Schlumberger array: Commonly used in Europe, it is similar to the Wenner, except thatthe spacing between the two center electrodes is made smaller than that between the othertwo. In operation, the inner electrodes remain fixed and the outer electrodes are moved.The test is repeated changing the spacing between the inner electrodes. Dipole–dipole array: The source dipole is separated from the receiving dipole and the dis-tances between the two dipoles are varied.Pole–dipole array (not shown in Figure 1.32): One of the current electrodes is placed at adistance from the survey area approximately 5 to 10 times the desired survey depth. Thereceiving dipoles are stepped away from the current electrode, providing resistivity meas-urements that are reasonably representative of media encountered at a specific depth anddistance from the current electrode.Operational ProceduresWith a battery as a direct-current source, a current flow is established between the twoouter electrodes. The current drop is detected by the two inner electrodes and recorded on46 Geotechnical Investigation MethodsTABLE 1.11Typical Resistivity Values for Geologic MaterialsaResistivityMaterials ΩΩ ft ΩΩ mClayey soils: wet to moist 5–10 1.5–3.0Silty clay and silty soils: wet to moist 10–50 3–15Silty and sandy soils: moist to dry 50–500 15–150Bedrock: well fractured to slightly fractured with 500–1000 150–300moist soil-filled cracksSand and gravel with silt About 1000 About 300Sand and gravel with silt layers 1000–8000 300–2400Bedrock: slightly fractured with dry soil-filled cracks 100–8000 300–2400Sand and gravel deposits: coarse and dry �8000 �2400Bedrock: massive and hard �8000 �2400Freshwater 67–200 20–60Seawater 0.6–0.8 0.18–0.24a From Soilest, Inc.Note: (1) In soils, resistivity is controlled more by water content than by soil minerals. (2) The resistivity of thepore orcleft water is related to the number and type of dissolved ions and the water temperature.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 46the potentiometer, and the “apparent” resistivity (Wenner array) is computed from theexpressionρ�(2πAE)/I (1.3)where ρ is the soil resistivity, A the distance between electrodes (in cm), E the differentialpotential between intermediate electrodes (in V), and I the current flowing between endelectrodes (in A).“Apparent” resistivity signifies an average value resulting from layering effects.In vertical profiling, the electrode spacing is increased while the resistivity changes arerecorded, and a curve of resistivity vs. electrode spacing is drawn as shown in Figure 1.31.As the value of resistivity obtained is largely dependent upon material resistivities to adepth equal to the electrode spacing A, material changes can be inferred from the changein the slope of the curve. For any given depth, in terms of electrode spacing, the lateral variations in resistivity are measured by moving the rear electrode to a front position and marching the array laterally. Subsurface conditions are inferred from the variations invertical and lateral values. In multilayered systems, interpretations must be correlatedwith test borings.To interpret vertical profiling, a set of empirical curves (Wetzel–Mooney curves) is usedto estimate the depth to an interface and the resistivity. The curves, log–log plots ofapparent resistivity vs. electrode separation, are matched to the curves drawn from thefield data.Exploration 47BatteryElectrodeGroundsurfaceCurrentflow linesA A ANonpolarizingelectrodesSoil with low resistivityRock with high resistivityElectrode spacing (A)Soil Rock20100500040003000ρ (Ω cm)ρ =ρ = resistivity (Ω cm)A = electrode spacing (cm)E = difference in potential between intermediate electrodes (V)I = current flowing between end electrodes (A)20001000030 40 50(a)(b)2πAEIMilliammeter PotentiometerE = volts I = AmperesC1P2 P1C2FIGURE 1.31(a) Components of the electrical resistivity apparatus and the common four- electrode configuration of theWenner array. (b) Typical resistivity curve. (From ASTM, Symposium on Surface and SubsurfaceReconnaissance, Philadelphia, 1951. Copyright ASTM International, reprinted with permission.) CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 47Underground Coal Mine StudyA colleague advised the author of a study of an underground coal mine, where an expertin electrical resistivity used a “pole–dipole” method. Three different signatures wereobtained, as shown in Figure 1.33: intact rock, caved rock, and voids. The signatures, ini-tially considered as anomalies, were confirmed by core borings and comparisons with oldmine maps.Railway Tunnel Through Poor Quality RockDahlin et al. (1996) report on a resistivity investigation for a railway tunnel in Sweden. Theimaging system consisted of a resistivity meter, a relay-matrix switching unit, four elec-trode cables, a computer, steel electrodes, and various connectors. The total length ofinvestigation was of the order of 8200 m to depths of 120 m. Color-coded results showedvariation in rock quality along the entire proposed alignment. Low resistivities indicatedvery poor rock. Core borings confirmed the interpretations.48 Geotechnical Investigation MethodsSchlumberger array(a)(b)(c)VA M N BoVAaIIIVna aM N Bo o osWenner arrayDipole−dipole arrayAB source dipoles, MN receiving dipolesFIGURE 1.32Electrode (array) configurations for resistivity measurements. (From ASCE Technical Engineering and DesignGuides, adapted from the U.S. Army Corps of Engineers, 1998.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 48LimitationsSince resistivity is a function of water content and soluble salts, materials with widely dif-fering engineering properties can have the same resistivity. Therefore, correlations fromone location to another may not be possible. Differentiation between strata may not bepossible where the overlying material has an extremely high resistance.Water-table location often limits the depth for practical study because conductivity risessharply in saturated materials and makes differentiation between horizons impossible.Exploration 49Lateral distance (f t)Apparent resistivity (Ω)Intact rock signatureCaved rock signatureVoid signature* Typical response ranges in ohmsI - 10×102*I - 5×103*6 - 35×103*FIGURE 1.33Results of electrical resistivity study for coal mine using pole–dipole method. (Courtesy of Woodward–ClydeConsultants.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 49Because of the difficulties of relating measured resistivity values to specific soil or rocktypes, subsurface conditions are usually inferred from the vertical and lateral variations inthe measured values. In multilayered systems, interpretations must be confirmed by cor-relations with test boring data and, in general, electrical resistivity should be consideredas a preliminary exploration method.Electrical Conductivity (EM) SurveysApplicationsTerrain conductivity meters read directly the apparent conductivity, and interpretation ofprofiles is usually qualitative, based on showing anomalies that are then investigated byother methods. Some applications are:● Mapping nonorganic contamination of groundwater, which usually results in anincrease in conductivity over “clean” groundwater. An example is acid minedrainage.● Mapping soil and groundwater salinity.● Mapping depth to basement rock.● Locating buried metal tanks and drums.● Locating buried mine adits.Operational ProceduresConductivity is compared with resistivity in Figure 1.34. The electrical conductivity meter,the Geonics EM 34, uses two dipoles which can be used in either the vertical or horizontalmode. A single dipole, in the horizontal mode, is shown in Figure 1.35. Each mode gives asignificantly different response. One person carries a small transmitter coil, while a secondperson carries a second coil that receives the data from the transmitter coil. Electrical con-tact with the ground is not required and rapid exploration to depths of 60 m are possible.The electrical conductivity meter, EM 31 (Figure 1.36), is operated by one person.Exploration is rapid, but the effective depth of exploration is about 6 m.Underground Mine StudyOld maps indicated that an adit for a lead–zinc mine was located somewhere in an area to be developed for expensive home construction. The general area had suffered from50 Geotechnical Investigation MethodsConductive end plates(area A)Ammeter (current I )Battery (voltage V )Resistivity (� ) � = R ALIVwhere R = ΩConductivity (�)� = G LAVI/mΩ mwhere G = ΩΩ FIGURE 1.34Resistivity vs. conductivity.CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 50occasional ground collapse in the old mines. The area was surveyed using an EM34 andthe results identified an anomaly with 0 Ω (Figure 1.37). Continuous airtrack probes andcore borings confirmed that the mine was at a depth of about 40 ft.Ground-Probing Radar (GPR)ApplicationsGround-probing (ground-penetrating) radars are used as a rapid method of subsurfaceprofiling. They are designed to probe solids relatively opaque to radar waves, such aspavement-reinforcing rods and bases, as well as subpavement voids, buried pipes,bedrock surfaces and overlying boulders, caverns, tunnels, clay zones, faults, and ore bod-ies. Images consist essentially of wavy lines. They are difficult to interpret and primarilylocate anomalies that require additional investigation.Theoretical BasisEnergy is emitted in the radio portion of the electromagnetic spectrum (Figure 1.4), of which some portion is reflected back to the radar equipment. Various materials have differing degrees of transparency to radar penetration.New GPRs are digital with an improved signal-to-noise ratio using fiber optics cables and improved antennadesign.Exploration 51FIGURE 1.35Terrain conductivity meter (EM34). (Courtesy of Geonics.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 51TechniquesContinuous subsurface profiling by impulse radar, also termed electromagnetic subsurfaceprofiling (ESP), provides a registration of a continuously reflected radar pulse similar to seismic reflection images. A sled-mounted antenna is towed behind a small vehicle orboat containing the ESP system. It has been used since 1970 to locate buried sewer linesand cables, evaluate pavement conditions, detect voids, and profile the bottoms of rivers52 Geotechnical Investigation MethodsFIGURE 1.36Terrain conductivity meter (EM31). (Courtesy of Geonics.)EM34 Data vertical dipole mode quadrature phaseline #15 (8+00)80.00 90.00 100.00 110.00 120.00 130.00 140.00Offset (f t)150.00 160.00 170.00 180.00 190.00 200.00 210.005.004.003.002.001.000.00ΩFIGURE 1.37EM34 survey profile to locate a lead–zinc mine ca. 1860: 0U was found to be the location of the mine. (Courtesyof Woodward–Clyde Consultants.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 52and lakes. The ESP technique provides clear images in low-conductivity materials such assand, freshwater, or rock, and poor results in high-conductivity materials such as wet claybecause the penetration depth is limited by the strong attenuation of the signal.Magnetometer SurveysApplicationsMagnetometer surveys are used for the detection of magnetic ore bodies or rocks that arestrongly magnetic, such as the crystalline types as differentiated from sedimentary types.They are seldom used for engineering studies.Theoretical BasisMany rocks contain small but significant quantities of ferromagnetic materials which varywith rock type. The weak magnetization modifies the Earth’s magnetic field to an extentthat can be detected by sensitive instruments.Operational ProcedureMagnetometers provide the measurements and, when towed behind aircraft, they cancover large areas and provide appreciable data in a relatively short time.Data PresentationContour maps are prepared showing lines of equal value that are qualitatively evaluatedto locate anomalies indicative of ore bodies or rock-type changes.Gravimeter SurveysApplicationsIn their normal geologic application, gravimetric or microgravity surveys, are used for thedetection of major subsurface structures such as faults, domes, anticlines, and intrusions.Gravimetric surveys have been used in engineering studies to detect cavities in limestoneand the location of old mine shafts (Ghatge, 1993). Modern instruments are extremely sen-sitive, however, and the requirement for the precise determination of surface elevationsmay cause the application of the method to be relatively costly.Theoretical BasisMajor geologic structures impose a disturbance on the Earth’s gravitational field. The partof the difference between the measured gravity and theoretical gravity, which is purely aresult of lateral variations in material density, is known as the Bouguer anomaly. Other fac-tors affecting gravity are latitude, altitude, and topography, and have to be require con-sidered during gravitational measurements to obtain the quantity representing theBouguer anomaly.Gravimeters consist of spring-supported pendulums similar in design to a long-periodseismograph.Data PresentationIsogal maps are prepared showing contours of similar values given in milligals (mgal) toillustrate the gravity anomalies. (Note: 1 mgal � 0.001 gal; 1 gal � acceleration due to grav-ity � 1 cm/s2.)Exploration 53CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 53Cavity Exploration in Soluble Rock The bulk density of limestones is about 160 pcf (2.6 g/cm3), and that of soils generallyranges from 100 to 125 pcf (1.6 to 2.0 g/cm3). In karst regions, a gravity-low anomaly mayindicate an empty cavity, a cavity filled with low-density material, or a change in soil orgroundwater conditions. Microgravimetric instruments have been developed in recentyears which permit a precision of 0.01 mgal (10 µgal) or better (Greenfield, 1979), equiva-lent to a change in soil thickness of about 10 in. (24 cm) for a density contrast between soiland rock of 62.4 pcf (1.0 g/cm3). A detected anomaly is then explored with test borings.Infrared ThermographyAn infrared scanner, which can detect very small variations in temperature, is mounted ona sled that can be towed by a person or a vehicle. Multicolor images are displayed andrecorded. Cooler areas are depicted in green or blue and the warmer areas in orange or red.In engineering studies, infrared scanners are most useful in detecting water leaks in sewersor water lines. In limestone areas, such leaks are often precursors to sinkhole development.1.3.3 Reconnaissance MethodsGeneralReconnaissance methods of exploration are divided into two general groups as follows:● Large excavations allow close examination of geologic materials and include testpits, test trenches, and large-diameter holes, which can be made relatively rap-idly and cheaply. Adits and tunnels, although costly to excavate, are valuable forinvestigating rock mass conditions.● Hand tools and soundings provide low-cost and rapid means of performing prelim-inary explorations. Samples are recovered with the hand auger and 1in. retractableplug sampler, and probings with bars provide indications of penetration resistanceto shallow depths. The cone penetrometer test (CPT) and the standard penetrationtest (SPT) are used also as reconnaissance methods for preliminary explorations.MethodsThe various methods are summarized in Table 1.12, including:● Test pit or trench excavation● Large-diameter holes● Adits and tunnels● Bar soundings● Hand auger or posthole digger● One-inch retractable plug sampler● Continuous penetrometer test (see Sections 1.34 and 2.4.5)● Standard penetration test (see Section 2.4.5)1.3.4 Continuous CPT(ASTM D5778)HistoryIn 1932, the Dutch developed a simple device to measure continuously soil properties insitu. At the end of steel rods was a penetrometer consisting of a cone tip. Over the years,the rods were advanced by driving them with a hammer (dynamic force), applying dead54 Geotechnical Investigation MethodsCRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 54Exploration 55TABLE 1.12Reconnaissance Methods of ExplorationMethodApplicationsProcedureLimitationsTest pit or trench ●Detailed examination of soil strata●Excavation by backhoe, bulldozer, ●Usually limited in depth by water excavation●Observation of groundwater seepageor by handtable (GWL), rock depth, or ●Identification of GWL●Can be extended below GWLby reach of equipment●Recovery of disturbed or undisturbed samples sheeting and pumping if soils have ●Can be dangerous if left above GWLand in situdensity tests at least some cohesionunsheeted and depths are above 4 to 5 ft●Examination of fault zones●Examination of miscellaneous and rubble fills●Identification of rock surface and evaluation of rippability●Borrow material investigationsLarge-diameter holes●Detailed examination of strong ●Holes 60 to 100 cm in diameter ●Strong cohesive soils withno cohesive soil strata and location ofexcavated by rotating large augerdanger of collapse slickensides and other details affecting bucket (Figure 1.52), or excavated ●Rock penetration limited except stability and seepageby handby calyx drilling (Section 1.4.5)Adits and tunnels●Used in rock masses for preparation of detailed ●Excavation by rock tunneling ●Very costlygeological sections and in situtesting; methods●Rock masses that do not require lining forprimarily for large dams and tunnelssmall-diameter tunnels are left open for relatively short time intervalsBar soundings ●To determine thickness of shallow ●Ametal bar is driven or pushed into ●No samples obtainedstratum of soft soilsground●Penetration limited to relatively weak soils such as organics or soft claysHand auger or ●Recovery of disturbed samples and ●Rotation of a small-diameter auger ●Above GWLin clay or granular posthole diggerdetermination of soil profile to shallow depths into the ground by handsoils with at least apparent cohesion●Locate GWL(hole usually collapses in ●Below GWLin cohesive soils with soils with little to slight cohesion)adequate strength to prevent collapse●Penetration in dense sands and gravels or slightly plastic clays can be very difficultOne-inch retractable-●Blows from driving give qualitative ●Small-diameter casing is driven into ●The entire rod string must be plug samplermeasure of penetration resistance to depths ground by 30 lb slip hammer removed to recover sampleof 30 m in soft claysdropped 12 in.●Penetration depth in strong soils limited ●One-inch diameter samples can be ●Samples are obtained by retracting ●Small-diameter samplesretrieved up to 1 m in lengthdriving plug and driving or pressing the casing forwardContinuous cone ●Continuous penetration resistance ●Probe is jacked against a reaction for ●No samples are recoveredpenetrometer including side friction and point continuous penetration(CPT)(see Sections resistance for all but very str ong soils on 1.3.4 and 2.4.5)land or waterStandard penetration ●Recovery of disturbed samples and ●Split-barrel sampler driven into ●Penetration limited to soils and test (SPT)(see Section determination of soil profileground by 140 lb hammer soft rocks. Not suitable for 2.4.5)●Locate GWLdropped 30 in.boulders and hard rocksCRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 55weights (static force), or pushing hydraulically. Initially, only penetration resistance at thecone tip was measured (qc or qt). Later, a cone was developed with a sleeve to measureshaft (side) friction fs (Begemann cone) in addition to tip resistance. The Begemann conewas termed a subtraction cone. It measures the total sleeve plus tip force on the cone andthe tip resistance when pushed into the ground. Sleeve friction is calculated by subtract-ing the tip resistance from the total resistance.Fugro, ca. 1965, developed an electric cone (the compression cone) that measured andrecorded both tip resistance and shaft friction separately. Some electric cones have a max-imum value for sleeve friction of the order of 20 tons. The subtraction cone has no sleevefriction limit; the only limit is the total penetrometer force. Subtraction cones can be usedwhere sleeve friction is high, such as in very stiff clay, and the limit of the electric cone isexceeded.CPT OperationsModern cones are pushed continuously into the ground by a hydraulic-force apparatusreacting against a machine. The apparatus can be mounted on a variety of platforms,including truck or track mounts, small portable units, and barges or drill ships. The inte-rior of a truck-mounted CPT is shown in Figure 1.38a. Large modern rigs have capacitiesof up to 30 metric tons. CPT rigs are often mounted with test boring drill rigs, but the reac-tion force is limited. Advanced by hydraulic thrust, the electric cones employ load cells and strain gages thatmeasure electronically both tip resistance and local sleeve friction simultaneously. Theresults are recorded digitally at the surface with an accuracy of measurement of usuallybetter than 1%. Readings are usually taken at 5 cm intervals. Cones vary in size with areasof 10 and 15 cm2 the most common because ASTM criteria apply. The 15 cm2 cones canpush well in loose gravels, cemented sands, and very stiff fine-grained soils and weath-ered rock. Various cone sizes are shown in Figure 1.38b. The CPT method permits rapid and economical exploration of thick deposits of weak tomoderately strong soils and provides detailed information on soil stratification. Therehave been many modifications to cone penetrometers in the past 20 years. The test canmeasure in situ many important soil properties applicable to geotechnical and environ-mental studies as summarized below. The interpretation of strength and compressibilityproperties are covered in Section 2.4.5.Although soil sampling is possible with a special tool, soil samples are normally notobtained. CPT data are usually confirmed with test borings and soil sampling, but thenumber of borings is significantly reduced.See also ASTM D5778, Sanglerat (1972), Schmertmann (1977), and Robertson et al. (1998).Engineering ApplicationsStandard CPT. The common application of the CPT is to obtain measurements of engi-neering strength properties. In relatively permeable soils, such as fine and coarser sands,pore pressure effects during penetration at standard rates often have negligible influence,and the CPT measures approximately fully drained behavior. In homogeneous, plasticclays, the CPT measures approximately fully undrained behavior. Mixed soils produce in-between behavior.Piezocones are currently in common use (CPTU). They have a porous element near the tipand a built-in electric transducer to measure pore water pressure in addition to tip resist-ance and shaft friction. Information on stratification and soil type is more reliable than thestandard CPT. The interpretation of material strength properties is improved, and data areobtained on deformation characteristics. To obtain pore-pressure data, penetration is56 Geotechnical Investigation MethodsCRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 56stopped at the desired depthand readings are taken until the pore pressure generated bythe penetration has dissipated. The coefficient of consolidation (ch) and the coefficient forhorizontal hydraulic conductivity (kh) are determined. Hole inclination is also recordedwith the piezocone illustrated as in Figure 1.39a. A plot of a CPTU log showing point andshaft friction, friction ratio, pore pressures, and a soil log is given in Figure 1.40. CPT plotsnow normally include the friction ratio and, with the CPTU, pore pressure measurements.Exploration 57FIGURE 1.38 (a)Cone penetrometer test equipment: (a) interior of CPT truck showing hydraulic force apparatus. (Courtesy ofFugro.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 57The seismic cone penetration test (SCPT) (Figure 1.39a) combines the piezocone with themeasurement of small strain shear wave velocities (P and S waves). A small geophone oraccelerometer is placed inside a standard cone, and seismic wave velocities are measuredduring pauses in cone penetration. A hammer blow to a static load on the surface can pro-vide the shear wave source. Explosives can be used offshore or the “downhole seismictest” onshore. The results have been used for evaluating liquefaction potential (Robertson,1990).The active gamma penetrometer (GCPT) (Figure 1.39b) measures in situ soil density. Thetest is particularly important in clean sands, that are difficult to sample in the undis-turbed state.58 Geotechnical Investigation MethodsFIGURE 1.38 (b)Cone penetrometer test equipment: (b) various cone sizes. (Courtesy of ConeTec.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 58A vision cone penetrometer (VisCPT) has been developed recently to overcome the prob-lem of no recovered samples (Hryciw et al., 2002). Miniature cameras are installed in theCPT probe, and continuous images of the soil’s stratigraphy are obtained through syn-thetic sapphire windows mounted in the side of the probe.Exploration 59Triaxial geophonesor accelerometer(Vp & Vs)Load cellsInclinometer (I )Gamma rayexcitationGamma probePhoto multipliertubeInsulationLoad cellsPorous filterelement Cone tip (Qc)Cone tip (Qc)Pore pressuretransducer (U )Thermistor (T )Inclinometer (lx & ly)ElectrodesTriaxial geophonesor accelerometer(Vp & Vs)Csl crystalActive sourceThermistor (T )Friction sleeve (Fs)Pore pressuretransducer (U )Porous filterelementFriction sleeve (Fs)(a) (b) (c)FIGURE 1.39Various types of cone penetrometers. (a) Piezo cone penetrometer (CPTU): measures tip resistance, shaftfriction, pore pressures, temperature, inclination, and shear wave velocities. (b) Active gamma penetrometer:GCPT measures in situ soil density, particularly useful in sands which are difficult to sample undisturbed. (c) Electrical resistivity cone (RCPT): provides measures of relative soil resistivity. (Courtesy of ConeTec.)Site: 2001 CPTBTLocation: Test siteCone: 10TONAD 010Date: 12:08:9411:530 12SBTU metresRf%Fs barQt bar0−0.0−5.0−10.0−15.0Depth (m)−20.0−25.0−30.0Max. depth: 45.75 mDepth Inc: 0.05 mSBT: Soil behavior type (Robertson et al., 1990)Estimated phreatic surfaceSample 6Sample 5Sample 4Sample 3Sample 2Sample 1Drilled Out Drilled Out Drilled Out250 0.0 2.5 0.0 5.0 0 120SandSandSandSandSilty sand/sandSilty sand/sandSilty sand/sandSilty sand/sandSilty sand/sandSilty sand/sandSilty sand/sandSilty sand/sandSiltSiltSiltClayey siltClayey siltClayey siltClaySensitive finesSandSandSandFIGURE 1.40Sample of CPTU log. Data plots are provided in real time. (Courtesy of ConeTec.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 59Environmental ApplicationsCone penetrometers have been modified for environmental studies and the identifica-tion of contaminants (Robertson et al., 1998). Sensors have been developed to measuretemperature, pH, radioactivity (gamma), resistivity, ultraviolet-induced fluorescence,and total petroleum hydrocarbons and other contaminants. SCAPS (site characterizationand analysis penetrometer system) is a program in use by the government agencies inwhich the cone penetrometer is used for hazardous waste site characterization. An elec-trical resistivity cone (RCPT) is shown in Figure 1.39c.Classification of MaterialsCorrelationsCPT values are influenced by soil type and gradation, compactness, and consistency,which also affect the relationship of qc with fs. Correlations have been developed betweencone-tip resistance (qc is also referred to as cone-bearing capacity) and the friction ratio Rf (� fs/qc) to provide a guide to soil classification as given in Figure 1.41. These charts donot provide a guide to soil classification based on grain size, but rather on soil behaviortype. Figure 1.41 is based on data obtained at predominantly less than 30 m, and overlapbetween zones should be expected (Robertson, 1990).It has been found that cones of slightly different designs will give slightly different val-ues for qc and fs, especially in soft clays and silts. This apparently is due to the effect thatwater pressures have on measured penetration resistance and sleeve friction because ofunequal end areas. It has also been recognized that overburden pressure increases withdepth also affecting strength values, as it does with the Standard Penetration Test results.60 Geotechnical Investigation MethodsCone resistance, qc (MPa)Cone resistance qc (bars) (1 bar = 100kPa = 1.04tsf)11 very stiff fine-grained12-11 over consolidated or cemented12 Sa-ClSa3 Clay1 Sensitivefine-grained2 Organic material10GSa- Sa9 Sa8 Sa-SiSa6 SaSi-ClSi5 ClSi-SiCl4 SiCl-Cl7 SiSa-SaSi1001010.10 1 2 3 4Friction ratio (Rf) (sleeve friction/cone bearing) % (Rf=fs/qc)5 6 7 81000100101FIGURE 1.41Simplified soil behavior type classification for standard electric friction cone. (Adapted from Robertson, P.K.,et al., Proceedings, In situ ’86, Blacksburg, VA, 1986.)CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 60For these reasons, correction factors have been proposed for the strength parameters andcone geometry. For equal end area cones only qt is normalized. It is noted that cone resist-ance qc is corrected to total cone resistance qt as follows (Robertson, 1990):qt�qc�(1-a)u (1.4)where u is the pore pressure measured between the cone tip and the friction sleeve and ais the net area ratio.New classification charts have been proposed based on normalized data (Robertson, 1990). Operations OffshoreGeneralOffshore shallow-water investigations, such as for ports and harbors, normally involvewater depths of 3 to 30 m. Jack-up rigs or spud barges are used and the cone is pushedfrom the vessel by conventional methods. A drill casing is lowered to the seafloor to pro-vide lateral support for the CPT rods.For offshore deep-water exploration, such as for oil-production platforms, the CPT isusually operated in conjunction with wire-line drilling techniques (Section 1.3.5), withequipment mounted on large vessels such as shown in Figure 1.42. The major problem,maintaining adequate thrust reaction from a vessel subjected to sea swells, can be over-come by a motion compensator and the drill string. Thrust reaction can be provided byweighted frames set on the seafloor as shown in Figure 1.42.Seafloor Reaction SystemsUnderwater cone penetrometer rigs that operate from the seafloor have been developed byseveral firms. The Fugro-McClelland system, called “Seaclam,” operates in water depths upto 300 m. A hydraulic jacking system, mounted in a ballasted frame with a reentry funnel,is lowered to the seabed (Figure 1.43). Drilling proceeds through the Seaclam and whensampling or testing is desired, a hydraulic pipe clamp grips the drill string to provide areaction force of up to 20 tons. A stringof steel rods, on which the electric friction cone ismounted, is pushed hydraulically at a constant rate of penetration. Data are transmitteddigitally to the drill ship.ConeTec have developed an underwater CPT that can operate in water depths up to2500 ft that can penetrate to 30 ft below the mudline. It is lowered over the side of a steelvessel and set on the seafloor. Fugro also has an underwater ground surface CPT whichpresently has a penetration of about 6 m.Sampling and In Situ TestingThe various underwater sampling and in situ tools using the Fugro Seaclam are illustratedin Figure 1.43. Some sampling and testing is obtained by free-falling down the drill pipe.Fugro have developed the “Dolphin” system for piston sampling, in situ CPT, and vaneshear testing to water depths of at least 3000 m. Tools that require controlled thrust foroperation, such as the cone penetrometer and piston sampler, employ a mud-poweredthruster assembly at the base of the drill string. Vane testing and push sampling do notrequire the use of the thruster.The Dolphin cone penetrometer is illustrated in Figure 1.44, and a plot of cone resistancedata is shown in Figure 1.45. Penetration distances are 3 m or may refuse penetration atless than 3 m, and tip resistance and side friction are recorded. Drilling advances the holeto the next test depth and the CPT repeated. The remote vane shear device is shown inExploration 61CRC_42742_Ch001.qxd 9/21/2006 5:37 PM Page 61Figure 1.46 and a data plot is shown in Figure 1.47. The vane data, compared withundrained laboratory test results from piston samples, are shown in the figure.1.3.5 Test and Core BoringsPurposeTest and core borings are made to:● Obtain samples of geologic materials for examination, classification, and labora-tory testing62 Geotechnical Investigation MethodsTop drivepowerswivelMotioncompensationsystem5" drill stringSeabedreactionand re-entryframeseaclamRe-entryfunnelSeafloorDownholehydraulicpush samplerwipsamplerOpendragbitDownholeCPT systemwisonLine tensionerHydraulicpipe clampFIGURE 1.42Schematic diagram of the operational procedures from a drill ship. Shown are the Fugro Seaclam for deepwater drilling, push sampling, and in situ testing using a cone penetrometer. (Courtesy of Fugro.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 62● Permit in situ measurements of the physical and engineering properties of thematerials● Obtain information on groundwater conditionsBoring TypesThey may be classified according to sampling operations:● Wash sample borings are made to recover completely disturbed samples for general classification only.● Sample borings are made to recover partially disturbed samples (SPT) or undis-turbed samples (UD).● Core borings are made to recover rock cores.● Rotary probes recover only rock cuttings and are made to provide a rapid deter-mination of the bedrock depth.● Air track probes result in rock cuttings at the surface and are made to provide arapid determination of rock quality.Operational ElementsThe execution of a boring requires fragmentation of materials, removal of the materialsfrom the hole, and stabilization of the hole walls to prevent collapse.FragmentationMaterials in the hole are fragmented for removal by:● Circulating water in loose sands or soft clays and organic soils● Chopping while twisting a bit by hand (wash boring), or rotary drilling or auger-ing in moderately strong soilsExploration 63CPT/CPTUseismic CPTUElec. cond. CPTPushsamplingPistonsamplingAmbientpressuresamplingHeatflowdataIn situvaneCPTUpermea-meterDilato-meter(NGI)Bat-probe(NGI)FIGURE 1.43Various sampling and in situ testing tools used with the Fugro Seaclam (see Figure 1.42). BAT probe is anelectrical resistance piezometer. (Courtesy of Fugro.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 63● Blasting or rotary drilling with a rock bit for “floating” boulders● Rotary or percussion drilling in rockMaterial RemovalMaterials are removed to form the hole by:● Dry methods used in cohesive soils, employing continuous-flight augers abovethe water table and the hollow-stem auger above and below the groundwaterlevel (GWL).● Circulating fluids from a point in the hole bottom, which is the more common pro-cedure, accomplished by using clean water with casing, mud slurry formed64 Geotechnical Investigation MethodsOvershot knobMeteringcylinderDrill pipeRemotememory unitCone rodConeBoreholeLanding ringDrilling fluidDrill bitSoil formationFIGURE 1.44The Dolphin Cone Penetrometer.(Courtesy of Fugro.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 64either naturally or with additives used without casing, or air pressure in highlyfractured or cavernous rock where circulating water is lost and does not returnto the surface.Hole StabilizationSome form of stabilization is often needed to prevent hole collapse. None is required instrong cohesive soils above GWL. Casing, used in sands and gravels above the water table, in most soils below GWL, andnormally in very soft soils, is usually installed by driving with a 300 lb hammer, although140 lb hammers are often used with lighter tripod rigs. The hollow-stem auger serves as cas-ing and wireline and Odex methods install casing by drilling.Driven casing has a number of disadvantages:● Installation is slow in strong soils and casing recovery is often difficult.● Sampling at stratum changes is prevented unless they occur at the end of adriven section, and in situ testing is limited.● Obstacles such as boulders cannot be penetrated and require removal by blast-ing or drilling. The latter results in a reduced hole diameter which restricts sam-pling methods unless larger-diameter casing is installed before drilling.● Loose granular soils below GWL tend to rise in casing during soil removal,resulting in plugged casing and loosened soils below.● Removal of gravel particles is difficult and requires chopping to reduce particlesizes.● Casing plugged with sand or gravel prevents sampler penetration adequate forrecovery of undisturbed samples and representative SPT values. (The drill rodlength and sampling tool must be measured carefully to ensure that the samplerrests on the bottom slightly below the casing.)Mud slurry, formed naturally by the mixing of clayey soils during drilling, or by theaddition of bentonite, is a fast and efficient method suitable for most forms of samplingand in situ testing.Exploration 65Penetration below seafloor (f)1000 100 200Cone resistance, qc (ksf)300 400 500 600 700 800 900100120130140150160170180LegendClaySandFIGURE 1.45Plot of cone resistance data. (Courtesy ofFugro.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 65There are several disadvantages to mud slurry:● Hole closure may occur in soft soils or crushed, porous materials such as shell beds.● Relatively large pumps are required to circulate the slurry, particularly whenboring depths exceed 30 ft (10 m).● Mud-cased holes do not permit accurate water level readings, unless environmen-tally friendly biodegradable muds are used. Such muds incorporate an organicsubstance that degrades in a period of 24 to 48 h, allowing GWL measurements.● Excessive wear on pumps and other circulating equipment occurs unless sandparticles are removed in settling pits.● Mud may penetrate some soils and contaminate samples.● Mud loss is high in cavity-prone and highly fractured rock.Grouting is used where closure or hole collapse occurs in fractured or seamy zones inrock masses. Cement grout is injected into the hole in the collapsing zone and then the holeis redrilled.66 Geotechnical Investigation MethodsOvershot knobLanding ringBoreholeDrill bitDrilling fluidSoil formationVane bladeReaction vaneMotor housingRemote memory unitMechanical pawlsDrill pipeFIGURE 1.46The Dolphin Remote Vane. (Courtesy ofFugro.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 66Boring Inclination● Vertical borings are normal in soil formations and most rock conditions duringinvestigation.● Angle borings are often drilled in rock masses to explore for joints, faults, or solu-tion cavities, or for the installation of anchors in soil or rock.● Horizontal borings are drilled to explore for tunnels or the installation of rock bolts,instrumentation, or horizontal drains. Maintaining a straight horizontal boring isextremely difficult. At the start of the boring, gravity tends to pull the drill bitdownward; then as penetration increases, gravity acts on the heavy drill string andthe bit may tend to drift upward. Rock quality variations will also cause inclinationchanges. New technology employs directional drilling (Civil Engineering, 1998).Standard Drilling Machines and ToolsThere are a large number of hole-making methods and drilling machines. A summary isgiven in Table 1.13 in terms of application, method, advantages, and limitations. The basicExploration 67Undrained shear strength (ksf)Penetration (ft)Undrained shear strength (ksf)20010000 1.0 2.0 3.0 4.03004005002.50 200 400Time (sec.)Deepwater siteGassyRemote vane data3.0-in. pushed data2.25-in. driven dataBlade : SmallDepth : 33.0 & 35.0 (ft)S u=1.00 S u=1.04600 800 10002.01.51.00.50FIGURE 1.47Remote vane results compared with lab testresults from push samples. (Courtesy ofFugro.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 6768 Geotechnical Investigation MethodsTABLE 1.13Comparison of Various Drilling Machines and MethodsMachineApplicationDrilling MethodsAdvantagesLimitationsTripod with block and tackle ●Procure soil samples●Hole advanced by ●Requires only ●Slow operation, especially (Figure 1.48) or motor-driven ●Exploratory boringschopping while twistingminimum-skill laborbelow 10 mwinchfor preliminary rods and washing with ●Almost any location●Penetration difficult in strong soils studiespump-circulated wateraccessible to the light, and impossible in rockportable equipment●Difficult to remove gravel from ●Holes for some types ●Commonly called wash-casing; leads to poor samplesof in situtestingboring method●UD sampling difficult except in verysoft soils because of lack of reactionRotary Drills●Procure all types of ●Hole advanced by cutting ●Relatively rapid●Equipment access in swampy Skid-mounted (Figure 1.49)soil and rock samplesbit on end of power-driven ●Can penetrate all or rugged terrain difficultTruck-mounted (Figure 1.50)●Make hole for many rotating drill rod to which types of materials●Requires trail or roadTrailer-mountedtypes of in situtesting pressure is applied ●Suitable for all types ●Requires level platform for drillingTrack-mounted●Drilling inclined hydraulicallyof samples●Efficiency of drilling varies withholes in soil or rock ●Hole normally retained by rig sizefor horizontal drains mud slurryor anchorsContinuous-Flight Auger ●Drill small- to ●Rotating continuous ●Rapid procedure for ●Hole collapses when auger is (Figure 1.54)moderate-size holeflights of helical augersexploratory boringwithdrawn from weak cohesivefor continuous but●Removal of all flights in strong cohesive or cohesionless granular soils,disturbed samples allows soil examinationsoils and soft rockthereby limiting depth, usually●Other samples ●SPT sampling to near water tablepossiblepossible when hole ●Auger samples disturbed●Normally used in cohesiveremains open after●Sampling methods limitedsoils with adequate auger removal●Requires rig samples and soil strength to prevent stratum examination modificationopen hole collapseHollow-Stem Auger(Figure 1.51)●Drill small- to ●Similar to continuous- ●Rapid method in ●Penetration in strong soils to moderate-size holes flight auger, except hollow weak to moderately significant depths or through for soil samplingstem is screwed into strong soilsgravel layers difficult, and not ground to act as casing●SPT and UD possible through boulders and rocksampling possible●Considerable disturbance may occur from auger bitCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 68Exploration 69Large-Diameter Augers●Drill large-diameter ●Rotating large-diameter ●Rapid method●Depth limited by groundwater (Figure 1.52)holes (to 4 ft) for auger cuts soil to form hole●Enables close and rock conditionsBucket augerdisturbed samples examination of ●Large machine requires Disk auger and soil strata subsurface soil easy accessHelical augerexamination in conditions●Not suitable in cohesionless soils, cohesive soils where soft clays, or organic soilshole remains open●Samples disturbedPercussion drills(cable-tool or ●Commonly used to ●Heavy bits are raised and ●Relatively economical●Equipment large and cumberchurn-drilling)drill water wellsdropped to break up method of makingsome●Recovers “wash” materials and form alarge-diameter●Slow progress in strong soils samples in bailersslurry which is removed by holes through anyand rock●Define rock depthbailers or sand pumps. material ●Disturbance around bit from high-Casing retains the hole(up to 2 ft [60 cm])energy impact seriously affects SPT values●Rock coring and UD sampling not possibleHammer drills●Water wells●Similar to percussion●Relatively rapid ●Similar to percussion drills,●Exploratory holes ●Diesel pile-driving penetration through except progress is much more through cobbles and hammer used to drive cobbles and bouldersrapidbouldersdouble-wall casing while circulating air through annulus to blow cuttings from inner barrelPneumatic percussion drill(Air ●Drilling Holes for ●Percussion rock bit chips ●Rapid procedure for ●Samples are only small chips. track probes, Figure 1.52)●Rock anchorsand crushes rock with making small-Not used for sampling. ●Blastinghammer blows as bit diameter holes in ●Possible to lose entire drill stem ●Rock characterizationrotates. Chips removed by hard rockin loose, fractured rock, clay air pressureseams, wet shale, etc.●Best use is hard massive rockImpact drill●Rapid drilling of ●Pneumatically energized ●Very rapid ●Limited to rock massesexploratory hole in rock.tungsten carbide bit penetration in rock ●No sample recovery(One case: 640-ft. hole, hammers hard rock at as masses. Could be ●Danger of hole closure in loose 6.5-in. diameter,high a rate as 700used to drill pilotfractured or seamy rock zones. drilled in 24 h)blows/minholes to substantial (Could be corrected by cement depths for tunnelinjection and redrilling)studies, and core rockat critical depthswith rotary methodsCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 69components required for test or core borings include a drilling machine, casing, drill rods,drilling bits, and sampling tools.Drilling machines consist of a power source, a mast for lifting apparatus, and a pump forcirculating water or mud (or a compressor for air drilling) to lower, rotate, and raise thedrilling tools to advance the hole and obtain samples. Test borings for obtaining represen-tative or undisturbed samples under all conditions are normally made by rotary drills, andunder certain conditions, with the tripod, block, and tackle. Some of the more commonmachines are illustrated in Figures 1.48 through 1.51.Exploratory holes in which only disturbed samples are obtained are made with contin-uous-flight augers, large-diameter augers in clays or by percussion or hammer drilling inall types of materials. Large-diameter augers (Figure 1.52) can provide holes of diametersadequately large to permit visual examination of the borehole sides for detailed logging,if the inspector is provided with protection against caving. Pneumatic percussion andimpact drills advance holes rapidly in rock, without core recovery. Casing is used to retain the hole in the normal test boring operation, with tripods orrotary machines, at the beginning of the hole and for the cases described under HoleStabilization. Boring cost is related directly to casing and hole size. Standard sizes and70 Geotechnical Investigation MethodsFIGURE 1.48The wash boring method. The hole is advanced by hand by twisting a bladed bit into the soil as water underpressure removes cuttings from the hole. In the photo, a 140 lb hammer is being positioned before driving anSPT sample.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 70dimensions are given in Table 1.14; casing is designed for telescoping. There are severaltypes of casing as follows:● Standard drive pipe has couplings larger than the outside pipe diameter and isused for heavy-duty driving.● Flush-coupled casing has couplings with the same diameter as the outside pipediameter. For a given diameter, it is lighter and easier to drive because of itssmooth outside surface than a standard pipe, although more costly to purchase.● Flush-jointed casing has no couplings and is even lighter in weight than flush-coupled casing, but it is not as rugged as the other types and should not be driven.Drill rods connect the drilling machine to the drill bits or sampler during the normal testor core boring operation with rotary machines (or tripods for soil borings). Standard sizesare given in Table 1.14. Selection is a function of anticipated boring depth, sampler types,and rock-core diameter, and must be related to machine capacity. The more commondiameters are as follows:● “A” rod is normally used in wash boring or shallow-depth rotary drilling to takeSPT samples. In developing countries, a standard 1 in. pipe is often substitutedfor wash borings because of its low weight and ready availability.● “B” rod is often used for shallow rotary core drilling, especially with light drillingmachines.● “N” rod is the normal rod size for use with large machines for all sampling and cor-ing operations; it is especially necessary for deep core drilling (above 60 ft or 20 m).● “H” rod is used in deep core borings in fractured rock since it is heavier andstiffer than “N” rod and will permit better core recoveries.Exploration 71FIGURE 1.49A skid-mounted rotary drilling machine which advances the hole in soil or rock with a cutting bit on the endof a power-driven rotating drill rod to which pressure is applied by a hydraulic ram. In the photo, the drillrods are being lowered into the hole before the hole is advanced.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 71Drilling bits are used to cut soil or rock; some common types are shown in Figure 1.53.Chopping bits (others such as fishtail or offset are not shown) are used for wash borings.Drag bits (fishtail or bladed bits) are used for rotary soil boring. They are provided withpassages or jets through which is pumped the drilling fluid that serves to clean the cut-ting blades. The jets must be designed to prevent the fluid stream from directly imping-ing on the hole walls and creating cavities, or from directing the stream straightdownward and disturbing the soil at sampling depth. Low pump pressure is alwaysrequired at sampling depth to avoid cavities and soil disturbance. Rock bits (tricone,roller bit, or “Hughes” bit) are used for rock drilling. Core bits (tungsten carbide teeth or diamonds) are used for rock coring while advancing the hole. Sizes are given in Table 1.14.Sampling tools are described in Section 1.4.Standard Boring Procedures1. Take surface sample. (In some cases, samples are taken continuously from thesurface to some depth. Sampling procedures are described in Section 1.4.2.)72 Geotechnical Investigation MethodsFIGURE 1.50Rotary drilling with a truck-mounted Damco drill rig using mud slurry to prevent hole collapse. Rope on thecathead is used to lift rods to drive the SPT sampler, which in the photo is being removed from the hole. Ahydraulic piston applies pressure to rods during rock coring, or during pressing of undisturbed samples. Thetable supporting the hydraulic works is retractable to allow driving of SPT samples or casing.CRC_42742_Ch001.qxd 9/21/2006 5:38 PMPage 722. Drive “starter” casing or drill hollow-stem auger to 5 ft penetration (1 m pene-tration in metric countries).3. Fragment and remove soil from casing to a depth of about 4 in. (10 cm) below thecasing to remove material at sampling depth, which will be disturbed by the forceof the plugged casing during driving. Completely disturbed “wash” samples (cut-tings) may be collected at the casing head for approximate material classification.Exploration 73FIGURE 1.51Rotary drill rig advancing boring with the continuous hollow-stem flight Auger.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 7374 Geotechnical Investigation MethodsClearancecutterClearancecutterToothedcutterlipHelical(b)(a)HelicDiscCutterCutterRockbucketCutterBarrelHinged bottomChopping bitHand trip forunloadingBarrelShutterplateFIGURE 1.52(a) Heavy-duty auger machine excavating with a large-diameter barrel bucket. Generally suitable only in soilswith cohesion where the hole remains open without support. (b) Types of large augers. (From USBR, EarthManual, U.S. Bureau of Reclamation, Denver, Colorado, 1974.)TABLE 1.14Standard Sizes of Drill ToolsaO.D. I.D. Weight Coupling O.D.Size in. mm in. mm lb/ft kg/m in. mmDrill Rods — Flush CoupledEb 1 5/16 33.3 7/8 22.2 2.7 4.0 7/16 11.1Ab 1 5/8 41.3 1 1/4 28.5 3.7 5.7 9/16 14.3Bb 1 7/8 47.6 1 1/4 31.7 5.0 7.0 5/8 15.9Nb 2 3/8 60.3 2 50.8 5.2 7.5 1 29.4EWc 1 3/8 34.9 15/16 23.8 3.1 4.7 7/16 11.1AWc 1 3/4 44.4 1 1/4 31.8 4.2 6.5 5/8 15.9BWc 2 1/8 54.0 1 3/4 44.5 4.3 6.7 3/4 19.3NWc 2 5/8 66.7 2 1/4 57.1 5.5 8.4 1 3/8 34.9HWc 3 1/2 88.9 3 1/16 77.8 7.7 11.5 2 3/8 60.3Casing — Flush JointedEW 1 13/16 43.0 1 1/2 38.1 2.76 4.2AW 2 1/4 57.2 1 29/32 48.4 3.80 5.8BW 2 7/8 73.9 2 3/8 60.3 7.00 10.6NW 3 1/2 88.9 3 76.2 8.69 13.2HW 4 1/2 114.3 4 101.6 11.35 16.9PW 5 1/2 139.7 4 7/8 127.0 15.35 22.8SW 6 7/8 168.3 6 1/32 152.4 19.49 29.0UW 7 5/8 193.7 7 177.8 23.47 34.9ZW 8 5/8 219.1 8 3/32 203.2 27.80 41.4(Continued)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 74Exploration 75TABLE 1.14(Continued)O.D. I.D. Weight Coupling O.D.Size in. mm in. mm lb/ft kg/m in. mmCasing — Flush CoupledEX 1 13/16 46.0 1 5/8 41.3 1.80 2.7 1 1/2 33.1AX 2 1/4 57.2 2 50.8 2.90 4.4 1 29/32 48.4BX 2 7/8 73.0 2 9/16 65.1 5.90 8.8 2 3/8 69.3NX 3 1/2 83.9 5 3/16 81.0 7.80 11.8 3 76.2HX 4 1/2 114.3 4 1/8 104.8 8.65 13.6 3 15/16 100.0O.D. I.D. Weight Coupling O.D.Size (in.) in. mm in. mm lb/ft kg/m in. mmCasing — Standard Drive Pipe2 2 3/8 60.3 2 1/16 52.4 5.5 8.3 2 7/8 73.02 1/2 2 7/8 73.0 2 15/32 62.7 9.0 13.6 3 3/8 85.73 3 1/2 88.9 3 1/16 77.8 11.5 17.4 4 101.63 1/2 4 101.6 3 9/16 90.5 15.5 23.4 4 5/8 117.34 4 1/2 114.3 4 1/32 102.4 18.0 27.2 5 3/16 131.8Casing — Extra Heavy Drive Pipe2 2 3/8 60.3 1 15/16 49.2 5.0 7.6 2 7/32 56.42 1/2 2 7/8 73.0 2 21/64 59.1 7.7 11.6 2 5/8 66.73 3 1/2 88.9 2 29/32 73.8 10.2 15.4 3 1/4 82.53 1/2 4 101.6 3 23/64 85.3 12.5 18.9 3 3/4 95.34 4 1/2 114.3 3 53/64 97.2 15.0 22.7 4 1/4 107.8Diamond Core BitsDCDMA Standards Core Diam. (Bit I.D.) Hole Diam. (Reaming Shell O.D.)Size in. mm in. mmEWX and EWM 0.845 21.5 1.485 37.7AWX and AWM 1.185 30.0 1.890 48.0BWX and BWM 1.655 42.0 2.360 59.9NWX and NWM 2.155 54.7 2.930 75.72 3/4 in., 3 7/8 in. 2.690 68.3 3.875 98.44 in., 5 1/2 in. 3.970 100.8 5.495 139.68 in., 7 3/4 in. 5.970 151.6 7.755 196.8Wireline SizeAQ 1 1/16 27.0 1 57/64 48.0BQ 1 7/16 36.5 2 23/64 60.0NQ 1 7/8 47.6 2 63/64 75.8HQ 2 1/2 63.5 3 25/32 96.0PQ 3 11/32 85.0 4 53/64 122.6a From Diamond Core Drill Manufacturers Association (DCDMA).b Original diamond core drill tool designations.c Current DCDMA standards.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 754. Take sample.5. Advance hole through the next interval of 5 ft (or 1 m) by either driving casingand removing the soils, as in step 3, or using a mud slurry or the hollow-stemauger to retain the hole, and take sample.6. Continue sequences until prescribed final boring depth is reached. (In deep bor-ings, or supplemental boring programs, sampling intervals are often increased to10 or even 20 ft [3–6 m].)7. When rock is encountered, set casing to the rock surface to permit coring withclean water to keep the bit cool and clean and prevent clogging.8. Record casing lengths; measure and record drill rod and bit length and drill rodand sample tool length each time that the hole is entered to ensure that the holebottom is reached, that the hole is not collapsing if uncased and that the sampleris at the required depth below the casing or final boring depth prior to sampling.Other Drilling Machines and MethodsContinuous Hollow-Stem Auger (ASTM 5784-95) The hollow-stem auger has been used with increasing frequency in recent years to avoidthe use of drilling muds to retain the hole (Figure 1.51). Its use, therefore, is common forenvironmental investigations. During advance, the auger flights remove the soil from thehole and the hollow stem serves as casing. A bottom bit cuts the soil and a removable plugon a rod prevents soil from rising in the hollow portion of the stem (Figure 1.54). At sam-pling depth, the inner rods and plug are removed and either disturbed (SPT) samples orundisturbed tube samples can be obtained. In “clean” sands and silts below the watertable, pressure equalization by filling the stem with water is usually necessary to preventthe saturated soils from entering the auger. Drilling is difficult or impossible in very hard76 Geotechnical Investigation MethodsFIGURE 1.53Several types of drilling bits. From left to right: three-bladed soil-cutting bits, tricone roller rock-cutting bits,carbolog-tooth bits for cutting soft rock, and diamond rock-coring bit.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 76soils, gravels, cobbles, or boulders. To save time, drillers may advance the stem withoutthe plug at the end. Below the water table, soils will rise in the hollow stem and samplingresults will be affected. Boring inspectors should always insist that the plug is in place dur-ing hole advance.Wireline DrillingWireline drilling eliminates the necessity of removing a string of drill rods for samplingand coring and is therefore a very efficient method for deep core drilling on land or off-shore. The coring device is integral with the drill rods, which also serve as casing.Normally, it is not necessary to remove the casing except when making bit changes. Thedrill string is a 4 to 6 in. pipe with a bit at the end. The drill string is rotated as the drillingfluid is pumped down through it. (In offshore drilling, the mud, mixed onboard, is nor-mally not recirculated, but rather flows up through the hole onto the seafloor.)Soil sampling, rock coring, and in situ testing are carried out from the inner barrelassembly (Figure 1.82). Core samples are retrieved by removal of the inner barrel assem-bly from the core barrel portion of the casing drill rods. An “overshot” or retriever is low-ered by the wireline through the drill rod to release a locking mechanism in the innerbarrel head. The inner barrel with the core is then lifted with the wireline to the surface,the core removed, and the barrel returned to the bottom. In deep holes, it is necessary topump the inner barrel into place with fluid pressure. Wireline core diameters are given inTable 1.14.Exploration 77Rod inside hollowstem for removingplugRemovable plugFlightBitFIGURE 1.54Continuous flight, hollow-stem auger.Plug at tip prevents soil from enteringthe stem during hole advance.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 77Odex DrillingOdex drilling is used to set casing in formations where hole collapse occurs and drillingwith mud is inefficient due to high mud loss. Such conditions include coarse and poroussoils, highly fractured rock, or rock with frequent cavities. It is also used to install mini-piles socketed into rock. The Odexdrill includes casing with a bit, and an inner core barrel. When drilling areamer on the Odex bit swings out and drills a hole larger than the external diameter ofthe casing. Cuttings are flushed from the casing with water or air. When the requireddepth has been reached, the drill is reversed and the reamer swings to its minimum diam-eter, allowing the bit to be lifted up through the casing, which remains in the hole. Rockdrilling continues with a drill bit or a core barrel. Data on rock quality can be monitoredelectronically, providing measures on penetration rates, thrust on the bit, rotation torque,rotation speed, fluid pressure, and cross section of the hole.Pneumatic Percussion Drills (Air Track Rigs) Air tracks (Figure 1.55) provide a rapid and efficient method of characterizing rock massesin terms of quality. Rates of penetration per second are recorded; the harder the rock thelower are the penetration rates as shown on the logs given in Figure 1.56. Rock chips,removed by air pressure, can be examined at the hole entrance. Rock core borings shouldbe drilled for correlations. Subaqueous DrillingVarious types of platforms for the drilling equipment and applications for subaqueous testborings are given in Section 1.4.4.Planning and Executing a Test Boring ProgramEquipment SelectionThe study phase, terrain features and accessibility, geologic conditions, boring depths, andthe sample types required are considered when a test boring program is planned.Boring Types● Exploratory borings are normally performed first to determine general subsurfaceconditions. Only disturbed samples, and at times rock cores, are obtained.● Undisturbed sample borings follow to obtain UD and perform in situ tests, usuallyin cohesive soils. ● Core borings are programmed to obtain rock cores.Boring SpacingIn the feasibility and preliminary studies, borings are located to explore surface boundariesand stratigraphy as depicted on an engineering geology map. Additional borings may berequired for increased definition. Grid systems may be appropriate in uniform conditionsand, depending on the study area, size may range in spacing from 100 to 300 ft (30 to 100 m).Final study programs depend upon the project type as follows:● Structures (buildings, industrial plants, etc.) in urban areas usually are requiredby code to be investigated by borings at spacings that provide at least one bor-ing for a given building area. In other than code-controlled areas, boring layoutdepends on building configuration, and spacing is generally about 50 to 100 ft78 Geotechnical Investigation MethodsCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 78(15 to 30 m) depending on the uniformity of geologic conditions, the importanceof the structure, and the foundation type.● Dams are usually investigated on a grid of about 50 to 100 ft (15 to 30 m) spacing.● Highway and railroad study programs depend on the adequacy of data obtainedduring the geologic mapping phase as supplemented by geophysical and recon-naissance studies (excavations, augers, probes, etc.), unless specified otherwiseby a highway department or other owner. A minimum program requires boringsin major cuts and fills, and at tunnel portals and all structure locations.● In all cases, flexibility must be maintained and the program closely observed topermit the investigation of irregular or unforeseen conditions as they appear.Exploration 79FIGURE 1.55Air track drilling in limestone for deep foundation investigation. Figure 1.56 gives airtrack logs from aninvestigation in limestone.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 79Boring DepthExcavations (open cuts for buildings, highways, subways, etc. and closed excavations fortunnels, caverns, mines) require borings adequately deep to explore to at least a shortdepth below final grade, or deeper if conditions are unfavorable, and to determine piezo-metric levels which may be artesian. The latter condition may require borings substan-tially below the final grade.Foundations for buildings and other structures require boring depths programed andcontrolled to satisfy several conditions. As a general rule, borings must explore the entirezone of significant stress (about 1½ to 2 times the minimum width of the loaded area) inwhich deformable material exists. (Note that significant stress can refer to that imposed bya controlled fill and the floor it supports rather than the foundations bearing the fill, or canrefer to stresses imposed at some depth along a pile group rather than at basement or floorlevel.)The primary objective is to locate suitable bearing for some type of foundation and tohave some knowledge of the materials beneath the bearing stratum. Drilling to “refusal”is never a satisfactory procedure unless the materials providing refusal to penetration(often inadequately defined by an SPT value) and those underlying have been previouslyexplored and adequately defined. In rock, penetration must be adequate to differentiateboulders from bedrock.SpecificationsBoring type (exploratory, undisturbed, and core boring), spacing and depth, sample typeand intervals, sample preservation and shipment, groundwater depths, and often drillingprocedures are covered in specifications provided to the boring contractor. Standard bor-ing specifications require modification to suit a particular project.80 Geotechnical Investigation MethodsDepth (ft)1520253035404550550510Air track log A9Soft Hard SoftAirAirVoidHardAir track log D8Depth (ft)152025303540455055105060555045403530Time (sec.)252015105060555045403530Time (sec.)2520151050FIGURE 1.56Air track logs from drilling in limestone. “Air” is soil drilling. Note voids on logs. Hard rock was defined asadvance �20 sec. (Courtesy of Woodward–Clyde Consultants.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 80Boring Surveillance (Inspection)During all phases of the boring program experienced surveillance should be provided toensure that the intent of the specifications is properly interpreted and executed, and thatthe desired results are achieved.Functions of the person performing the surveillance are generally as follows:1. Enforce the specifications.2. Maintain liaison with the structural engineer–architect and modify the programas necessary (add or delete borings, change types, depths and intervals of sam-pling, etc.).3. Ensure complete and reliable drilling information (accurate reporting of depths,proper drilling, and sampling techniques).4. Identify accurately all geologic conditions encountered and prepare reports andfield logs that include all pertinent information (Section 1.4.7).Some conditions where experienced geologic interpretations are necessary include:● Differentiating a fill from a natural deposit. Some granular fills may appear to benatural, when in reality they overlie a thin organic stratum, or contain zones oftrash and rubbish. Mistakenly identifying a deposit as fill can result in unneces-sarily costly foundations when local building codes prohibit foundations on fill.● Judging the recovered sample material to be wash remaining in the casing ratherthan undisturbed soil.● Determining groundwater conditions.● Differentiating boulders from bedrock on the basis of rock identification (boul-ders may be of a rock type different from the underlying bedrock, especially inglaciated terrain).Supplemental InformationMany types of devices are available for use in boreholes to remotely sense and log varioussubsurface conditions, which should be considered in the planning of any subsurfaceexploration program, as described in Section 1.3.6.1.3.6 Borehole Remote-Sensing and LoggingA number of devices and instruments can be lowered into boreholes to obtain a variety ofinformation. They are particularly useful for investigating geologic conditions in materi-als fromwhich it is difficult or impossible to obtain UD, such as cohesionless granular soilsand badly fractured rock masses. Applications, equipment, operation, and limitations ofvarious devices for remotely sensing and logging boreholes are summarized in Table 1.15.Borehole cameras (TV and photographic) furnish images of borehole walls in fracturedrock masses.Seisviewer, an ultrasonic acoustical device, is also used to obtain images of boreholewalls in fractured rock masses.The 3-D velocity probe (Figure 1.57) ranges up to 15 ft in length, 3 in. in diameter, andabout 150 lb in weight. It is lowered into the borehole to measure compression and shear-wave velocities, which provide information on fracture patterns in rock masses and, withthe gamma–gamma probe for density measurements, provide the basis for computingdynamic properties. The 3-D sonic logger was so named because the records show theamplitude and arrival times of the sonic energy for a given travel distance (between theExploration 81CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 8182 Geotechnical Investigation MethodsTABLE 1.15Borehole Remote-Sensing and Logging MethodsDeviceApplicationsEquipmentOperationLimitationsBorehole film Provides continuous Camera with conical or Camera lowered into In NX hole, depth limited to cameraundistorted record,rotating reflecting dry or water-filled hole about 150 m. Images with depth and orientation mirror, transmitter, illuminationof NX diameteraffected by water quality.controlled, of all geologic device, and compass containedLens has limited depth of planes in proper polar in assembly with length of 33 in.focus and cannot “see” coordinates in rock masses. and diameter of 2.75 in.depth ofopenings beyond Records fractures to 0.01 in.more than a few centimetersBorehole TV Examination of boreholes TV camera. Some can be fitted Camera lowered in to Resolution less thancamerain rock. Some types allow with zoon lens and powerfuldry, or water-filled holephotographic imageexamination of voids such miniature floodlight. as cavernsRecord can be tapedSeisviewerTo procure image of borehole Ultrasonic acoustical device Probe lowered into dry Rock masseswalls showing fractures and mounted in probe produces or water-filled holediscontinuities in rock massesimages of the entire hole3-D velocity probe To procure images of sonic Asonde from which a sonic pulse Sonde is lowered into Fracture patterns in rock (3-D sonic logger) compression and shear-wave is generated to travel into the borehole. Arrival times masses revealed a depth of (Figure 1.57)amplitudes and rock fracture rock mass (see the text)of compression and about 1 mpatterns. Vpand Vsused to shear waves are compute dynamic propertiestransmitted to surface,amplified and recordedMechanical Continuous measurement of Mechanical caliper connected Lowered into hole and Measures to about 32 in. calipersborehole diameter to to surface recorderspread mechanically as maximum in rock massuresdifferentiate soft from hard it is raised. Soft rock rock and swelling zones. gives large diameters Useful for undergroundfrom drilling operationexcavations in rockRecording To procure information on Recording thermometerLowered into borehole Rock masses and water-thermometersgroundwater flow and filled after fluid temperature filled holesevaluate grouting conditions stabilizesCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 82Exploration 83Electric well logTo obtain continuous record Devices to record parent Instrument lowered into Data are essentially of relative materialresistivities and spontaneousmud or water-filled qualitative for correlations characteristics and ground-potential (natural) generatedhole. Dry-hole devices with sample or core boringswater conditions from groundin borehole. Similar to availablesurface in all materialselectrical resistivelymeasurements from surfaceGamma–gamma To measure material density Nuclear probe measures Probe lowered into Measurements of in situprobein situ.Particularly useful back-scatter of gamma rays cased or mud-filled hole. densityin cohesionless soils and emitted from a source in the Back-scatter must be fractured rock massesaprobecalibrated for the casing or mudNeutron–gamma To measure material moisture Nuclear probe measures Probe lowered into Measurements of in situprobecontentin situabackscatter of gamma and cased or mud-filled hole.water contentneutron rays (resulting fromBack-scatter must be bombardment by fast neutrons),calibrated for the casing which gives a measure of or mud. Hydrogen hydrogen contents of materialscontent is correlatedwith the water orhydrocarbon contentScintillometerLocate shales or clay zones. Nuclear probe measures gamma Probe lowered into Qualitative assessments of Used primarily for petroleum rays emitted naturally from the borehole. Shales and shale or clay formationsexplorationmassclays have a high emission intensitycompared with sandsRock detector To differentiate boulders Microphone transmitter set Oneobserver listens to Area about 60–100m from (acoustic sounding from bedrockinto bedrock at various and series of holes drilled each geophone can be technique) locations to produce noise drilling sounds while investigated. In overburden,(Figure 1.58)which ismonitored with the other recordsdrill bits tend to clog in earphones and observed drilling depth for each clays and hole collapses and recorded by oscilloscopesignificant changebelow GWL. Best conditions Characteristic soundsare shallow deqosits of dry,enable differentiationare shallow deqosits of dry,between soil, boulders,slightly cohesive granularand rocksoilsTro-pariMeasure borehole inclination and direction (see text)aNuclear probes (gamma and neutron) have been used to monitor changes in moving slopes (Cotecchia, 1978) and even to locate the failure zone in a uniform deposit thatwas evidenced by a sudden change in change in density and moisture on a relatively uniform log.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 83transmitter and receiver). For velocity computations, the hole diameter must be knownand is measured with mechanical calipers.● Mechanical calipers are used to measure hole diameter in rock masses.● Recording thermometers are used to measure fluid temperatures in rock masses.● The electric well logger is used in soil and rock masses for continuous measure-ments of resistivity.● The gamma–gamma probe is used in soil and rock masses to obtain continuousmeasurements of in situ densities.● The neutron–gamma probe is used in soil and rock masses to obtain continuousmeasurements of in situ moisture contents.● The scintillometer is used to locate shales and clay zones in soil and rock masses.● The rock detector is an acoustical sounding device used to differentiate bouldersand other obstructions from bedrock. A geophone is set into bedrock and con-nected to an amplifier, headphone, and oscilloscope. A series of holes is drilledwith a wagon drill, or another drilling machine (Figure 1.58), while the observerlistens to the volume and nature of the generated sounds.● The Tro-pari surveying instrument is used to measure borehole inclination anddirection in relatively deep borings in good-quality rock. The instrument workswith a clockwork mechanism that simultaneously locks a plumb device and amagnetic compass when set in the borehole. The inclination and direction of theborehole, respectively, are read when the instrument is retrieved at the surface.1.3.7 Groundwater and Seepage DetectionGeneral Groundwater ConditionsFigure 1.59 illustrates various groundwater conditions, which are summarized as follows:● Static water table or level (GWL) is located at a depth below which the ground iscontinuously saturated and the water is at atmospheric pressure.84 Geotechnical Investigation MethodsP = wave pressureV = wave velocityBumperTransmitterAcoustic isolatorReceiverDrilling fluid (No scale)PpPpVpVpVsPbPbTPsPsRFIGURE 1.57Schematic of the principles of thethree–dimensional velocity probe. (FromMyung, J.T. and Baltosser, R.W., Stability ofRock Slopes, ASCE, New York, 1972, pp.31–56.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 84Exploration 85Headphone AmplifierCableRock drillSoilBoulderDrill bitRockGeophoneSound wavesFIGURE 1.58The elements of the rock indicator, oracoustical sounding technique, todifferentiate boulders from bedrock.Free-flowingartesian wellTopsoilSandClayClaySandSandSandandgravelRockSiltyclayPerched groundwater tableExcess hydrostaticor artesianpressureGWL − "static"groundwater level(free groundwatersurface)Confined orartesian waterFIGURE 1.59Various groundwater conditions.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 85● Perched water table can also be a measured GWL, and represents a saturated zoneoverlying an impervious stratum below which the ground is not saturated.● Artesian conditions result from groundwater under a head in a confined stratumwhich is greater than the static water-table head and can result in free flow at thesurface when the confined stratum is penetrated.● Variations in conditions occur with time, and are affected by seasonal conditions,tidal fluctuations, flooding, and pumping. Variations also occur with physicalconditions in terms of soil type and density, ground contours, surface drainage,rock-mass discontinuities, etc.Determining ConditionsTerrain analysis (Section 1.2.4, Interpretation of Topographic Maps) provides generalinformation on watertable location.Geophysical methods (seismic refraction and electrical resistivity) provide indirect meas-ures of the approximate depth to groundwater. Reconnaissance methods employing excavations locate the GWL in a positive manner butwithin a short time interval. Probable variations with time must always be considered dur-ing site analysis. Test pits are the best method for measuring short-term water levels andseepage rates. Auger borings may also clearly reveal the water table, especially in slightlycohesive soils. In cohesionless soils, the hole will tend to collapse within a few centimetersof the GWL but direct measurement is not usually possible.Test BoringsThe moisture condition of drive samples (SPT) may provide an indication of GWL.Samples will range from dry to moist to wet (saturated) as the GWL is approached. Thecondition should be noted on boring logs.In cased borings, the water level is generally determined by pumping or bailing water from the hole and permitting stabilization for 24 h. This method is reliable in uni-form sand strata or other pervious materials, but differentiating perched from static conditions is difficult. Site stratigraphy provides some clues for judgment. The method is unreliable when the casing terminates in an impervious stratum which blocks the entrance of water. The casing should be raised until it terminates in a permeable stratum.If the casing ends in an aquifer with an artesian head, water may flow from the casingwhen pumping ceases during drilling operations, or it may rise to a point above the esti-mated GWL.Casing water levels should be noted periodically during boring operations and for aperiod thereafter, and water loss as well as artesian and static conditions should benoted.Boring with a mud slurry will not provide reliable water level readings unless the holeis flushed with clean water or unless biodegradable mud is used for boring. After flush-ing, most holes in permeable soils collapse near or slightly above the perched or staticwater level.Borehole remote-sensing probes, such as the electric well logger and the neutron probe, pro-vide good indications of perched or static conditions.Piezometers (Section 3.4.2) provide the most accurate method of measuring groundwaterconditions, and are especially useful for recording changes with time. Measurementsmade during pumping tests performed at various levels are useful in differentiatingperched from static conditions.86 Geotechnical Investigation MethodsCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 86Seepage DetectionConditions of engineering significance include:● Flow through, around, and beneath earth dam embankments.● Flow beneath and around concrete dams.● Groundwater pollution as caused by flow from sanitary landfills, mine tailingsstorage areas, chemical waste ponds, etc.● Flows from slopes observable during site reconnaissance, depending on the season.Detection MethodsTracers placed in a water body may be useful in locating entrance points of seepage anddetecting exit points. Nonradioactive tracers include fluorescent and nonfluorescent dyes.Radioactive tracers include 82Br and 131I that are readily detectable with a Geiger–Mullercounter. Temperature can be sensed with a thermistor attached to the top of an insulatedaluminum-tipped probe inserted into the ground.Acoustical emission monitoring (Section 3.3.5) may detect large flows.1.4 Recovery of Samples and Cores1.4.1 GeneralObjectivesSamples of geologic materials are recovered to allow detailed examination for identifica-tion and classification, and to provide specimens for laboratory testing to obtain data ontheir physical and engineering properties.Sample Classes Based on QualityTotally disturbed samples are characterized by the complete destruction of fabric and struc-ture and the mixing of materials such as that occurring in wash and auger samples.Representative samples are partially deformed. The engineering properties (strength,compressibility, and permeability) are changed, but the original fabric and structurevary from unchanged to distorted, and are still apparent. Such distortion occurs withsplit-barrel samples.Undisturbed samples may display slight deformations around their perimeter, but for themost part, the engineering properties are unchanged. Such results are obtained with tubeor block samples.Sampler SelectionA number of factors are considered in the selection of samplers, including:● Sample use, which varies from general determination of material (wash sam-pler), to examination of material and fabric and in situ testing (split-barrel sam-pler), to performing laboratory index tests (split-barrel sampler), and to carryingout laboratory engineering-properties tests (UD).● Soil type, since some samplers are suited only for particular conditions, such assoft to firm soils vs. hard soils.Exploration 87CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 87● Rock conditions, since various combinations of rock bits and core barrels areused, depending on rock type and quality and the amount of recovery required.● Surface conditions, which vary from land or quiet water to shallow or deepwater with moderate to heavy swells.Some common sampling tools and their applications to various subsurface conditionsare illustrated in Figure 1.60. The various tools and methods and their applications andlimitations are described in Table 1.16.88 Geotechnical Investigation MethodsInspection is providedto control1. Correct driving energy2. Sampler type3. Sampler condition4. Sampling sequence5. Sample identification6. Sample preservation7. Condition at sampling depth8. Groundwater measurements9. Depth of boring10. Sample recovery − percentageSampler dropping on gravel or cinders not cleaned from casing, results in high blow countSoils loosened by overwashing. Blow count will be lower than true countSand under hydrostatic pressure plugging casing. Blow count will be higher than truePistonBWLSampler typeSplitbarrel (2-1/2" ID)Shelby tubeDenisoncoreborrelPiston orsplitbarrel(1-3/8" ID)splitbarrel(1-3/8" ID)splitbarrel(2-1/2" ID)Corebarrel-carboloy bitCorebarrel-diamond bitHard rockSoft rockGravelSandSilty SandHard clayFirm tostiff cloyOrganic siltor soft claySoil profilecinder fill172830"tree fanFIGURE 1.60Common sampling tools for soil and rock and their application.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 88Exploration 891.4.2 Test Boring Soil SamplingTypes Commonly UsedThe split-barrel sampler (SS) is used in all soil types for representative samples used for iden-tification and index tests.Thin-wall tubes are used in soft to firm clays and coring samplers are used in stiff to hardcohesive soils for undisturbed samples used for engineering properties tests.Required Boring DiametersWash or exploratory borings for split-barrel sampling are normally of 2½ in. diameter (cas-ing I.D.). UC borings are normally of 4 in. diameter, but may be larger to improve samplequality. Core borings vary from 2 in. to larger, normally with NX core taken in a holestarted with 4 in. diameter casing.Sampling IntervalSamples are normally prescribed for 5 ft (or 1 m) intervals and a change in strata.Samples should also be taken at the surface to record the topsoil thickness, and contin-uously from the surface to below the depth of shallow foundations to assure informa-tion at footing depth (5 ft intervals often do not provide information at shallow footingelevations).Continuous sampling is also important through miscellaneous fills that vary widely inmaterials and that often overlie a layer of organic soil, which may be thin but significant,and through formations with highly variable strata. In deep borings, sampling depths areoften changed to 10 or 20 ft intervals after several normally sampled borings are com-pleted and general subsurface conditions defined.Factors Affecting Sample QualitySampler Wall ThicknessA large outside diameter relative to the inside diameter causes deformation by materialdisplacement.Sampler Conditions● Dull, bent, or otherwise deformed cutting edges on the sampler cause sampledeformation.● Inside friction, increased by rust, dirt, or, in the case of tubes, omission of lacquer,causes distortions which are evidenced by a turning downward of layers, result-ing in conical shapes under extreme cases. Boring Operations● Dynamic forces caused by driving casing can loosen dense granular soils or den-sify loose granular soils.● Sands may rise in the casing when below the GWL (Figure 1.60).● Overwashing, jetting, and high fluid pressures also loosen granular soils orsoften cohesive materials (Figure 1.60).● Coarse materials often remain in the hole after washing, particularly in casedborings (Figure 1.60). These “cuttings” should be removed by driving a split bar-rel sampler, by pushing a Shelby tube, or with a cleanout auger. Contaminationis common after boring through gravel layers or miscellaneous fills containingcinders, etc.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 8990 Geotechnical Investigation MethodsTABLE 1.16Sampling Tools and MethodsCategory-Method and ToolApplicationLimitationsReconnaissanceWash sampleIndication of material type onlyCompletely mixed, altered, segregatedAuger sampleMaterial identificationCompletely disturbedRetractable-plug samplerMaterial identificationSlight disturbance, very small sample of soft soilsBlack sampleLarge undisturbed sample of cohesive materialsTaken from test pits, cohesive soils onlyTest Boring Sampling (Soils)Split barrel (spoon)Undisturbed samples in soils suitable Samples not suitable for engineering properties testing for identification and lab index testsSampling impossible in very coarse granular soilsShelby tubeUndisturbed sample in firm to stiff Will not retrieve very or clean granular soilscohesive soil. Can be driven into hard soilsStandard stationarypistonUndisturbed samples in soft to firm clays and siltsWill not penetrate compact sands, stiff clays, and other strong soils. Will not retrieve sands. Can be overpushedOsterberg piston sampler Undisturbed samples in all soils with cohesion except Usually cannot penetrate strong residual soil and very strong. Less successful in clean sandsglacial till. Some disturbance in sand and often loss of sample. User cannot observe amount of partial penetrationShear-pin piston (Greer and Undisturbed samples in all soils with Usually cannot penetrate strong residual soilMcClelland)cohesion except very strong. Often or glacial till. Disturbance in sandsrecovers samples in sands and can beCannot observe amount of partial penetrationused to determine natural densitySwedish foil samplerContinuous undisturbed samples in Gravel and shells will rupture foil. Cannot penetrate soft to firm cohesive soilsstrong soilsDenison samplerUndisturbed samples in strong cohesive soils Not suitable in clean granular soils, and soft to firm clayssuch as residual soils, glacial till, soft rock alternating Pitcher samplerSimilar to Denison above. Superior in Similar to Denison abovesoft to hard layers. Can be used in firm claysCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 90Exploration 91Subaqueous Sampling Without Test BoringFree-fall gravity coring tube Samples firm to stiff clays, sand and Maximum length of penetration about 5 m in soft fine gravel in water depths of 4000 msoils, 3 m in firm soilsHarpoon-type gravity Samples river bottom muds and silts to Penetration limited to few meters in soft soilssamplerdepths of about 3 mExplosive coring tube Small-diameter samples of stiff to hard Sample diameters only 1 7/8 in. Penetration only to 3 m (piggot tube)ocean bottom soils to water depths of 6000 mbelow seafloorGas-operated free-fall piston (NG)Good-quality samples up to 10 m depth from seafloorPenetration limited to 10 m below seafloorVibracoreUndisturbed samples of soft to firm bottomLimited to soft to firm soils and maximum penetration of sediment, 3 1/2 in. diameter to depths of 12 m12 m. Water depth limited to 60 mSubaqueous Sampling with Test BoringWireline drive sampleDisturbed sample in soilsPenetration length during driving not knownWireling push samplesRelatively undisturbed samples may be Often poor or no recovery in clean granular soilsobtained in cohesive materialsRock CoringSingle-tube core barrelCoring hard homogeneous rock where Circulating water erodes soft, weathered, or fractured rockhigh recovery is not necessaryDouble-tube core barrel Coring most rock types where high recovery is not Recovery often low in soft or fractured rocksnecessary, and rock is not highly fractured or softDouble-tube swivel-type Superior to double-tube swivel-core barrel, aboveNot needed in good-quality rock. Barrel is more costly core barrelParticularly useful to obtain high recoveryand complicated than others mentioned abovein friable, highly fractured rockWireline core barrelDeep hole drilling in rock or offshore because of No more efficient than normal drilling to depths of substantial reduction of in–out times for toolsabout 30 mOriented core barrelDetermination of orientation of geologic structuresProcedure is slow and costly. Requires full recoveryIntegral coring methodRecover cores and determine orientation in Slow and costly procedurepoor-quality rock with cavities, numerous fractures, and shear zonesCalyx or shot coringObtain cores in medium- to good-quality rock Slow and costly. Difficult in soft or seamy rockup to 2-m diameterCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 91● Hole squeezing may occur in soft clays if the drilling mud is too thin.● Plastic clays may remain along the casing walls if cleaning is not thorough.● Hollow stem augers can cause severe disturbances depending on the rate ofadvance and rotation, and the choice of teeth on the bit.● Hollow-stem augers must be advanced with the plug in the auger prior to sam-pling to prevent soil from entering the auger.Sampler InsertionAll ball check valves and other mechanisms should be working properly before the sam-pler is lowered into the hole. The sampler should be lowered to the bottom immediatelyafter the hole is cleaned. Measurements of the total length of the sampler and rods shouldbe made carefully to ensure that the sampler is resting on the bottom elevation to which thehole was cleaned and to avoid sampling cuttings. Since complete cleaning is usually notpractical, split-barrel samplers are seated under the rod weight and often tapped lightlywith the drive hammer; piston samples are forced gently through the zone of soft cuttings.Soil Factors● Soft to firm clays generally provide the best “undisturbed” samples, except for“quick” clays, which are easily disturbed.● Air or gas dissolved in pore water and released during sampling and storage canreduce shear strength.● Heavily overconsolidated clays may be subject to the opening of fissures fromstress release during boring and sampling, thereby substantially reducingstrength.● Gravel particles in a clay matrix will cause disturbance.● Cohesionless granular soils cannot be sampled “undisturbed” in the presentstate of the art.● Disturbance in cohesive materials usually results in a decrease in shear strengthand an increase in compressibility.Sample disturbance and its effect on engineering properties are described in detail byBroms (1980). See Section 1.4.6 for sample preservation, shipment, storage, and extraction.Split-Barrel Sampler (Split Spoon) (ASTM D1586-99)PurposeSplit-barrel samplers are used to obtain representative samples suitable for field examina-tion of soil texture and fabric and for laboratory tests, including measurements of grain-size distribution, specific gravity, and plasticity index, which require retaining the entiresample in a large jar.Sampler DescriptionSplit-barrel samplers are available with and without liners; the components are shown inFigure 1.61. O.D. ranges from 2 to 4½ in. A common O.D. is 2 in. with ¼ in. wall thickness(1½ in. sample). Larger diameters are used for sampling gravelly soils. Lengths are either18 or 24 in.A ball check valve prevents drill pipe fluid from pushing the sample out duringretrieval. To prevent sample spillage during retrieval, flap valves can be installed in theshoe for loose sands, or a leaf-spring core retainer (basket) can be installed for very soft92 Geotechnical Investigation MethodsCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 92clays and fine cohesionless soils. Upon retrieval, the barrel between the head and the shoeis split open (Figure 1.62), the sample is examined and described, removed, and stored.In some sampler types, brass liners are used for procuring drive samples of strong cohe-sive soils for laboratory direct-shear testing.Sampling ProcedureThe sampler is installed on the hole bottom, then driven into the soil with a hammer (nor-mally 140 lb) falling on the drill rods. The number of blows required for a given weightand drop height, and a given penetration, are recorded to provide a measure of soil com-pactness or consistency as described in Section 2.4.5 (Standard Penetration Test).Thin-Wall Tube SamplersPurposeThin-wall tube samplers are used to obtain UD of soft to stiff cohesive soils for laboratorytesting of strength, compressibility, and permeability.Tube MaterialsCold-drawn, seamless steel tubing (trade name “Shelby tube”) is used for most soil mate-rials; brass tubes are used for organic soils where corrosion resistance is required. Wallthickness is usually 18 gage; heavier gages are available. Lacquer coating can provide cor-rosion protection and reduce internal frictional resistance and sample disturbance.Tube diameters and lengths range from 2 to 6 in. in diameter, 24 to 30 in. in length. Tubes2 in. in diameter are used in 2½ in. exploratory borings, but 2 in. diameter samples have alarge ratio of perimeter disturbance to area and are considered too small for reliable labo-ratory engineering-property testing.Tubes 3 in. (2.87�) in diameter are generally considered the standard type for laboratorytest samples. The tube should be provided with a cutting edge drawn in to provide about0.04 in. inside clearance (or 0.5 to 1.5% less than the tube I.D.), which permits the sampleto expand slightly upon entering the tube, thereby relieving sample friction along thewalls and reducing disturbance.Tubes 4 to 6 in. in diameter reduce disturbance but require more costly borings. A 5 in.tube yields four samples of 1 in. diameter from the same depth for triaxial testing.OperationsThin-wall tubes are normally pressed into the soil by hydraulically applied force. Afterpressing, the sample is left to rest in the ground for 2 to 3 min to permit slight expansionExploration 93Hardened shoe Ball checkHardened shoe Outer split tubeSplit tubeThin wall liner(a)(b)Ball checkFIGURE 1.61The split-barrel sampler or split spoon: (a)without liner; (b) with liner. (Courtesy ofSprague and Henwood, Inc.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 93and an increase in wall friction to aid in retrieval. The rods and sampler are rotated clock-wise about two revolutions to free the sampler by shearing the soil at the sampler bottom.The sample is withdrawn slowly from the hole with an even pull and no jerking. In softsoils and loose granular soils, the sampler bottom is capped just before it emerges from thecasing fluid to prevent the soil from falling from the tube.Shelby Tube SamplingA thin-wall tube is fitted to a head assembly (Figure 1.63) that is attached to drill rod. An“O ring” provides a seal between the head and the tube, and a ball check valve preventswater in the rods from flushing the sample out during retrieval. Application is most satis-factory in firm to hard cohesive soils. In firm to stiff soils, the tube is pushed into the soilby a steady thrust of the hydraulic system on a rotary drilling machine using the machineweight as a reaction. Care is required that the sampler is not pressed to a distance greaterthan its length.94 Geotechnical Investigation MethodsFIGURE 1.62Split-barrel sample of sand.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 94Soft soils are difficult to sample and retain because they have insufficient strength topush the column of fluid in the tube past the ball check valve. In stiff to hard cohesivesoils, samples are often taken by driving heavy-gage tubes.Standard Stationary Piston SamplerA thin-wall tube is attached to a head assembly. The tube contains a piston (Figure 1.64),which is connected to a rod passing through the drill rod to the surface. When at the bot-tom of the tube, the piston prevents soil from entering the tube as it is lowered into thehole and permits seating through soft cuttings. The rod connected to the piston is heldfixed at the surface, while the hydraulic system on the drilling machine presses the tubepast the piston into the soil. With light rigs, the reaction can be increased by using Earthanchors. In properly fitted piston samplers, a strong vacuum is created to hold the samplein the tubes during withdrawal from the hole. The stationary piston sampler is used toretrieve very soft to firm cohesive soils.Osterberg Hydraulic Piston SamplerA thin-wall tube contains an actuating and a fixed piston (Figure 1.65). An opening in thehead assembly permits applying fluid pressure to the actuating piston at the top of the tube. Fluid pressure is applied to the actuating piston, which presses the tube past thefixed piston into the soil. The actuating piston eliminates the cumbersome rods of the standard stationary piston as well as the possibility of overpushing. The sampler iscommonly used for very soft to firm cohesive soils.Shear-Pin PistonThis device is similar to the Osterberg sampler except that the tube is attached to the pis-ton with shear pins, which permit the fluid pressure to build to a high value before it“shoots” the piston when the pins shear. The sampler can be used in soft to stiff cohesivesoils and loose sands. In loose sands disturbance is unavoidable. The “apparent” density,however, can be determined by measuring the weight of the total sample in the tube andassuming the volume calculated from the tube diameter and the stroke length. With theshear-pin piston, the sampling tube will almost always be fully extended because of thehigh thrust obtained.Double-Tube Soil Core BarrelsPurposeDouble-tube soil core barrels are used to obtain UD in stiff to hard cohesive soils, sapro-lite, and soft rock.Exploration 9530-in. brass tubeO-ringScrewsRubbersealBronze ballRetaining pinHead assemblyFIGURE 1.63Thin-wall “Shelby tube” sampler. (Courtesy of Sprague and Henwood, Inc.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 95Denison Core BarrelThe Denison core barrel is used in materials such as hard clays and cemented sands. Itincludes a rotating outer barrel and bit containing a fixed inner barrel with a liner, asshown in Figure 1.66. The cutting shoe on the inner barrel can extend below the cuttingbit. Liners range from 28-gage galvanized steel to brass and other materials such as phe-nolic-resin-impregnated paper with a 1/16 in. wall.Various bits are available for cuttingmaterials of varying hardness, to obtain samples ranging in diameter from 2 3/8 to 6 5/16in. Sample tubes range from 2 to 5 ft in length. The extension of the cutting shoe below thecutting bit is adjustable. The maximum extension is used in relatively soft or loose mate-rials, whereas in hard materials the shoe is maintained flush with the bit.During drilling, pressure is applied by the hydraulic feed mechanism on the drill rig tothe inner barrel, while the bit on the outer barrel cuts away the soil. The sampler is96 Geotechnical Investigation MethodsBuckets(leather) Piston assembly30-in. steel tubeScrewsPistonrod lockSpringHeadassemblyFIGURE 1.64Stationary piston sampler. (Courtesy of Sprague and Henwood, Inc.)Drill rodSampler headPistonPressurecylinderHollowpiston rodFixed pistonSoil sampleThin-walledsampling tubeHole inpiston rodWater returncirculationWater underpressureAir ventBall check(a) (b) (c)FIGURE 1.65Operation of the Osterberg piston sampler. (a) Sampler is set on cleaned bottom of borehole. (b) Hydraulicpressure propels sampling tube into the soil. (c) Pressure is released to through hole in piston rod. (From ENR,Engineering News Record, 1952. Reprinted with permission of McGraw-Hill.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 96retrieved from the hole, the cutting bit removed from the barrel (Figure 1.67), and the thinliners, retained in the inner tube by wall friction or a basket-type retainer, are removed.Pitcher SamplerThe operation of the Pitcher sampler is similar to that of the Denison core barrel exceptthat the inner barrel is spring-loaded and thus provides for the automatic adjustment ofthe distance by which the cutting edge of the barrel leads the coring bit (Figure 1.68).Because of adjusting spring pressure, the Pitcher sampler is particularly suited to sam-pling deposits consisting of alternating soft and hard layers.1.4.3 Miscellaneous Soil-Sampling MethodsWash SamplesCompletely disturbed cuttings from the hole advance operation carried to the surface bythe wash fluid and caught in small sieves or by hand are termed washed samples. Valueis limited to providing only an indication of the type of material being penetrated.Exploration 97Outer tube bitSaw tooth or carbida insert2 ft or 5 ft liner, stainless steel, brass or plasticRetainer basket typeInner tube shoeFIGURE 1.66Denison core barrel for hard soils. (Courtesy of Sprague and Henwood, Inc.)FIGURE 1.67Removal of the cutting bit from the Denison core barrel after coring cemented silty sands.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 97Auger SamplesCompletely disturbed cuttings from the penetration of posthole diggers (hand augers,Table 1.12), continuous-flight augers, or large-diameter augers are brought to the surfacewhen the auger is removed from the hole. In cohesive soils they are useful for soil identi-fication, moisture content, and plasticity index tests.Retractable Plug SamplerOne-inch-diameter tubes containing slightly disturbed samples are obtained in soft to firmorganic and cohesive soils suitable for soil identification and moisture content measure-ments (Table 1.12).Test Pit SamplesHigh-quality undisturbed block or “chunk” samples or small cylinder samples in softersoils with some cohesion are taken from test pits. Block samples are particularly useful insoils difficult to sample UD such as residual soils. Strong cohesive soils are sampled bycarefully hand-cutting a block from the pit walls. The sample is trimmed by knife andencased in paraffin on the exposed sides. The block is cut loose from the pit, overturned,and the remaining side is coated. It is then sealed in a box for shipment to the laboratory.Very large samples are possible.Weaker soils with some cohesion are carefully hand-trimmed into a small cylinder andsealed. The method has been used to obtain samples for density tests in partially saturatedsilty or slightly clayey sands.98 Geotechnical Investigation MethodsFluid under pressure "Soft" formationsDrill rodor pipeStaticfluid ventedto boreSliding valveclosedAll fluiddiverted to annular spaceHigh-velocityflush keepscutting areacleanDrill fluidflushescuttingsSpringprotectstube fromexcessivepressureFull-gagebore needsno reamingTube screwSampleprotectedfrom fluid"Hard" formationsFluid returnBall bearinghangerSliding valveopenValve sealCutter barrelShelby tubefully extended(a) (b) (c)FIGURE 1.68Operation of the Pitcher sampler: (a) down the hole; (b) sampling; (c) recovery. (Courtesy of Mobile Drilling Inc.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 98Swedish Foil SamplerHigh-quality continuous samples in soft, sensitive cohesive soils, useful in locating theshear zone in a slope failure problem, are possible with the Swedish foil sampler. A sam-pling tube, usually 8 ft in length, is pushed into the soil by a special drill rig as a reaction.To eliminate friction between the sample and the tube walls, thin steel strips, or foils,unroll to follow along the sampler walls as the sampler penetrates the soil.1.4.4 Subaqueous SamplingCategoriesSample procurement under subaqueous conditions can be placed in one of four generalcategories on the basis of the sampling technique:1. Normal cased-boring methods.2. Wireline drilling techniques.3. Sampling to shallow depths below the bottom without drill rigs and casing.4. Sample recovery from deep borings in offshore sands. Borehole remote-sensingand logging methods (Section 1.3.6), such as the electric well logger and nuclearprobes, should be considered since they provide important supplemental data.Normal Cased-Boring MethodsGeneralNormal cased borings require a stable platform for mounting the boring equipment andprocurement of samples. The up and down movements from swells severely affect drillingand sampling operations as bits and samplers are removed from contact with the hole bot-tom. Tidal effects require careful considerations in depth measurements.PlatformsFloats (Figure 1.69) or barges (Figure 1.70) are used in shallow water, generally less than 50ft (15 m) deep, with slight swells. Penetration depths are in moderate ranges, dependingon drill rig capacity.Large barges or jack-up platforms are used in water to depths of the order of 100 ft (30 m)with slight to moderate swells. Penetration depths below the bottom are moderatedepending upon the drilling equipment.Drill ships with wireline drilling techniques are used in deep water (Section 1.3.4 andFigure 1.42).Wireline Drilling MethodsGeneralWireline drilling techniques are used in deep water. Much deeper penetration depths arepossible than are with normal cased borings, and operations can tolerate much moresevere sea conditions than can cased borings.PlatformsLarge barges or moderately large ships are used in relatively calm water and water depthsover 50 ft (15 m), where deep penetration of the seafloor is required. Jack-up platforms areused where heavy swells can occur. Large drill ships (Figure 1.42) are used in deep waterwhere deep penetration below the seafloor is required.Exploration 99CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 99100 Geotechnical Investigation MethodsFIGURE 1.69Float-mounted tripod rig; casing is being driven prior to SPT exploratory sampling. FIGURE 1.70Barge-mounted rotary drill rig operating in the Hudson River for the third tube of the Lincoln Tunnel, NewYork City, a location with strong currents and heavy boat traffic.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 100SamplersDrive samplers (Figure 1.71): Either split-barrel samplers or tubes are driven with a 176 lb(80 kg) hammer dropped 10 ft (3 m) by release of a wire-hoisting drum. Penetration is onlyapproximated by measuring sample recovery since the sampler is attached to the wire, nottodrill rods. Recovery is related to the blow count for a rough estimate of relative density.Tube samples recovered in deep water at substantial depths below the seafloor in stiffclays will undergo significant strength decrease from stress release upon extraction fromthe seabed and extrusion in the shipboard laboratory.Pushed-tube and piston samplers: See Section 1.3.4 for operations offshore.Sampling to Shallow Penetration without Drill Rigs and CasingGeneralVarious devices and methods are available for sampling shallow seafloor conditions withoutthe necessity of mounting a drill rig on a platform and maintaining a fixed position forextended time intervals. Sampling procedure involves operating the equipment from the sideof a vessel equipped with a crane. Sampling is generally not feasible in strong materials or tobottom penetration depths greater than about 40 ft (12 m), depending upon the device used.Exploration 101WireDropweightDrivelengthSampletube(b)(a)FIGURE 1.71Wireline drive sampler: (a) before driving, (b) after driving. CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 101Sampling Methods and DevicesThe application, description, and penetration depths of the various devices and methodsare summarized in Table 1.17. The devices include the following:● Petersen dredge● Harpoon-type gravity corer (Figure 1.72)● Free-fall gravity corer● Piston gravity corer (Figure 1.73)● Piggot explosive coring tube● Benthos Boomerang Corer (Figure 1.74)● Vibracore (Figure 1.75) is the most practical method for obtaining long cores insoft soils in deep water. It can also be used on land to sample remotely contam-inated lagoons where a soft crust makes access hazardous to people.1.4.5 Rock CoringObjectivesRock coring is intended to obtain intact cores and a high percentage of core recovery.EquipmentRotary drilling machine, drill rods, a core barrel to receive the core, and a cutting bit areneeded.OperationsThe core barrel is rotated under pressure from the drill rig applied directly to it, whilewater flows through the head, down the barrel, out through the waterways in the bit, andup through the rock hole and casing (in soil) to return to the surface. When the rock is firstencountered in a borehole, the initial core runs are usually short because of the possibilitythat the upper rock will be soft and fractured. As rock quality improves, longer core runsare made.The core barrel is generally rotated between 50 and 1750 r/min; rotation speed is a func-tion of the bit diameter and rock quality. Slow speeds are used in soft or badly fracturedrocks and high speeds are used in sound hard rocks. If large vibrations and “chatter” ofthe drill stem occurs, the speed should be reduced or core recovery and quality will beseverely affected.Bit pressure is also modified to suit conditions. Low bit pressure is used in soft rocksand high pressure is used in hard rocks. When vibrations and “chatter” occur, the pres-sure, which is imposed hydraulically, should be reduced.Fluid pressure should be the minimum required to return the cuttings adequately to thesurface to avoid erosion of borehole walls. If there is no fluid return, drilling should imme-diately stop and the core barrel returned to the surface to avoid overheating the bit, whichwould result in bit damage (loss of diamonds) and possible jamming in the hole. Lack of fluid can result from:● Blockage of the core barrel, which occurs in clayey zones. Continued drillingafter a broken core has blocked entry into the core barrel results in core grinding.Indications of blockage may be heavy rod vibrations, a marked decrease in pen-etration rate accompanied by an increase in engine speed, return fluid moreheavily laden with cuttings than normal, and a rise in circulation fluid pressure.102 Geotechnical Investigation MethodsCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 102Exploration 103TABLE 1.17Subaqueous Soil Sampling Without Drill Rigs and CasingDeviceApplicationDescriptionPenetration DepthCommentsPetersen dredgeLarge, relatively intact Clam-shell type grab weighing about To about 4 in.Effective in water depths to 200 ft. “grab” samples of seafloor100 lb with capacity of about 0.4 ft3More with additional weightHarpoon-type Cores from 1.5 to 6 in. Vaned weight connected to coring tube To about 30 ftMaximum water depth depends gravity corer diameter in soft to firm soilsdropped directly from boadonly on weight. UD sampling (Figure 1.72)Tube contains liners and core retainerpossible with short, large-diameter barrelsFree-fall Cores 1.5 to 6 in. diameter Device suspended on wire rope over Soft soils to about 17 ft.As above for harpoon typegravity corer in soft to firm soilsvessel side at height of above seafloorFirm soils to(Figure 1.73)about 15 ft and then releasedabout 10 ftPiston gravity 2.5 in. sample in soft to Similar to free-fall corer, except that Standard core barrel Can obtain high-quality UD corer (Ewing firm soilscoring tube contains a piston that 10 ft; additional 10 ft samplesgravity corer)remains stationary on thesections can be addedseafloor during sampling Piggot explosive Cores of soft to hard bottom Similar to gravity corer. Drive weight Cores to 1 7/8 in. and Has been used successfully in coring tubesedimentsserves as gun barrel and coring tube to 10 ft length have20,000 ft of wateras projectile. When tube meets been recovered in resistance of seafloor, weighed gun stiff to hard materialsbarrel slides over trigger mechanism to fire a cartridge. The exploding gas drives tube into bottom sedimentsNorwegian Good-quality samples in Similar to the Osterberg piston About 35 ftGeotechnical soft clayssampler, except that the piston on theInstitute gas-sampling tube is activated byoperated piston gas pressureBenthos High-quality representative Weighed free-fall plastic core tube droped Up to 80 in. At times, less inRequires minimum water depth ofBoomerang corersamples in clays and sandsfrom a vessel penetrates the sea floor. dense sands33 ft. Has been used to depth(Figure 1.74)Floats inflate and rise to surface with of 29, 000 ftthe coreVibracore High-quality sample in softApparatus is set on seafloor. Air Length of 20 and 40 ftMaximum water depth of about (Figure 1.75)to firm sediments, diameterpressure from the vessel activates anRate of penetration varies 200 ft3 1/2 in.air-powered mechanical vibrator to with material strength.cause penetration of the tube, which Samples a 20 ft core in softcontains a plastic liner to retain the coresoils in 2 minCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 103104 Geotechnical Investigation MethodsWireTail finNonreturnvalveDead loadSamplecylinderCatcherFIGURE 1.72Harpoon-type gravity corer.Wire clampReleasemechanismWeight standPiston stopCore barrelThreaded jointPlastic linerPistonNose cone(core cutter)Pilot corer orpilot weightTripwireFreefallloopFIGURE 1.73Schematic diagram of a typical piston-type gravity corer. (From USAEC1996, Pub. EM 1110-1-1906. With permission.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 104● Loss in caverns, large cavities, or highly fractured zones. In Figure 1.76, a lightdrilling mud is being used to minimize fluid loss (note the mud “pit”), while cor-ing in limestone with highly fractured zones above the water table.When the prescribed coring length is obtained the core barrel is retrieved from theground. The core is removed from the barrel (Figure 1.77) and laid out in wooden boxesexactly as recovered (Figure 1.78). Wooden spacers are placed to divide each run. Thedepths are noted, the core is examined, and a detailed log is prepared.Core BarrelsThe selection of a core barrel is based on the condition of the rock to be cored and theamount and quality of core required. Core barrels vary in length from 2 to 20 ft, with 5 and10 ft being the most common.Table 1.18 provides summary descriptions of suitable rock conditions for optimumapplication, descriptions of barrel operation, and general comments. The types include:● Single-tube core barrel (Figure 1.79).● Double-tube rigid core barrel (Figure 1.80).● Swivel-type double-tube core barrel, of two types: conventional and Series M(Figure 1.81). These types usually provide the best core recovery and are themost commonly specified for rock coring.● Wireline core barrel (Figure 1.82).Exploration 105Pressure resisitantglass floatsElectronicflashing light48 In.521Hollow rubberball depresseslever(Ballcompresses andreleases at 30 to 45 ft)FloatreleaseleverButterflyvalve(open)WirePilot weight(down)Core cutterFloatsreleased3Plasticcoreliner80 In.Plastic coreliner containingsedimentStainless steelcore catcherBallast portion(expendable)4pilot weight (up)Benthos boomerang corer (model 1890)Maximum depth29,500 ftButtterflyvalve(clossed by releasedfloatsFIGURE 1.74The operating of sequence of theBoomerang Corer. (From USACE 1996,Pub. EM1110-1-1906. With permission.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 105● Oriented core barrel contains knives that scribe a groove on the rock core. Thecompass orientation of the groove is continuously recorded, which enablesdetermination of the strike of joints and other fractures (Figure 1.83). During nor-mal coring operations cores twist in the hole and accurate determination of jointstrikes are not reliable.Coring BitsGeneralTypes of coring bits are based on the cutting material, i.e., sawtooth, carbide inserts, anddiamonds.Waterways are required in the bits for cooling. Conventional waterways are passages cut intothe bit face; they result in enlarged hole diameter in soft rock. Bottom-discharge bits should be106 Geotechnical Investigation MethodsCore pipeAir-operatedmechanicalvibratorAir hosesandsignalcableFIGURE 1.75The Vibracore lowered to the seafloor.(Courtesy of Alpine Ocean SeismicSurvey, Inc.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 106used for coring soft rock or rock with soil-filled fractures. Discharge occurs behind a metalskirt separating the core from the discharging fluid, providing protection from erosion.Common bit sizes and core diameters are given in Table 1.14. The smaller diameters areused in exploratory borings for rock identification or in good-quality rock, but when max-imum core recovery is required in all rock types, NX cores or larger are obtained. In seamyand fractured rock, core recovery improves with the larger diameters, and HX size is com-monly used.Exploration 107FIGURE 1.76Core drilling with a Failing Holemaster. Light drilling mud is necessary in the fractured limestone above thewater table to prevent drilling mud loss.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 107Reaming shells, slightly larger than the core barrel diameter and set with diamonds orcarbide insert strips, ream the hole, maintaining its gage and reducing bit wear.Bit TypesSawtooth bits are the lowest in cost and have a series of teeth cut in the bit which are facedwith tungsten carbide. They are used primarily to core overburden and very soft rock.Carbide insert bits (Figure 1.53) have tungsten carbide teeth set in a metal matrix and areused in soft to medium-hard rocks.Diamond bits (Figure 1.53) are the most common type, producing high-quality cores inall rock types from soft to hard. Coring is more rapid, and smaller and longer cores areretrieved than with other bit types. The diamonds are either surface-set in a metal matrix,or the metal matrix is impregnated throughout with diamond chips. There are variousdesigns for cutting various rock types, differing in quality, size, and spacing of the dia-monds, matrix composition, face contours, and the number and locations of the water-ways.Core Recovery and RQDReporting MethodsPercent core recovery is the standard reporting method wherein core recovery is given as apercentage of total length cored. Rock Quality Designation (RQD) was proposed by Deere(1963) as a method for classifying core recovery to reflect the fracturing and alteration ofrock masses. For RQD determination, the core should be at least 50 mm in diameter (NX)and recovery with double-tube swivel-type barrels is preferred.108 Geotechnical Investigation MethodsFIGURE 1.77Removal of HX diameter limestone core from the inner barrel of a double-tube swivel-type core barrel.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 108RQD is obtained by summing the total length of core recovered, but counting only thosepieces of hard, sound core which are 10 cm (4 in.) in length or longer, and taking that totallength as a percentage of the total length cored. If the core is broken by handling ordrilling, as evidenced by fresh breaks in the core (often perpendicular to the core), thepieces are fitted together and counted as one piece.Exploration 109FIGURE 1.78Core recovery of 100% in hard, sound limestone: very poor recovery in shaley, clayey, and heavily fractured zones.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 109110 Geotechnical Investigation MethodsTABLE 1.18Types of Rock Core BarrelsCore BarrelSuitable Rock ConditionsOperation CommentsSingle tube (Figure 1.79)Hared homogeneous rock which Water flows directly around the core. Simple and rugged. Severe core loss in soft or resists erosionUses split-ring core catcherfractured rockDouble tube, rigid type Medium to hard rock, sound to Inner barrel attached to head and Water makes contact with core only in reamer (Figure 1.80)moderately fractured. Erosion-rotates with outer barrel as water flows shell and bit area, reducing core erosion.resistant to some extentthrough annular spaceHoles in inner tube may allow small flow around coreDouble tube, swivel typeFractured formations of average Inner barrel remains stationary, whileTorsional forces on core are eliminated (conventional series)rock hardness not excessively outer barrel and bit rotate. Inner barrel minimizing breakage. Core lifter may tilt andsusceptible to erosionterminates above core lifterblock entrance to inner barrel, or may rotate with the bit causing grinding of the coreDouble tube, rigid typeBadly fractured. Soft, or friable rock Similar to conventional series, except Superior to the conventional series. (series M)(Figure 1.81)easily erodedthat core lifter is attached to inner Blocking and grinding minimized.barrel and remains oriented. Erosion minimized by extended inner barrelInner barrel is extended to the bit faceWireline core barrelDeep core drilling under all rock See Section 1.3.4Retriever attached to wireline retrieves (Figure 1.82)conditionsinner barrel and core without the necessity of removing core bit and drill tools from the holeOriented core barrelDetermine orientation of rock Similar to conventional core barrels. Orienting barrel has three triangular hardened Oriented core (Figure 1.83)scribes mounted in the inner barrel shoe that cuts grooves in the cor e. Ascribe is alignedwith a lug on a survey instrument mounted in a nonmagnetic drill collar . The instrumentcontains a compass-angle device, multishot camera, and a clock mechanism. About 30 cm ofcoring the advance is stopped and a photograph of the compass clock, and lug is taken.Geologic orientation is obtained by correlation between photographs of the cor e grooves andthe compass photograph CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 110Causes of Low RecoveryRock conditions: Fractured or decomposed rock and soft clayey seams cause low recovery,for example, as shown in Figure 1.78. Rock quality can vary substantially for a given loca-tion and rock types as illustrated in Figuers 1.84 and 1.85, which show a formation of gran-ite gneiss, varying from sound and massive to jointed and seamy. Core recovery in theheavily jointed zone is illustrated in Figure 1.86.Coring equipment: Worn bits, improper rod sizes (too light), improper core barrel and bit,and inadequate drilling machine size all result in low recovery. In one case, in the author’sexperience, coring to depths of 30 to 50 m in a weathered to sound gneiss with light drillrigs, light “A” rods, and NX double-tube core barrels resulted in 40 to 70% recoveries and20 to 30% RQD values. When the same drillers redrilled the holes within a 1m distanceusing heavier machines, “N” rod and HX core barrels, recovery increased to 90 to 100%and RQDs to 70 to 80%, even in highly decomposed rock zones, layers of hard clay, andseams of soft clay within the rock mass.Coring procedure: Inadequate drilling fluid quantities, increased fluid pressure, improperdrill rod pressure, or improper rotation speed all affect core recovery.Integral Coring MethodPurposeIntegral coring is used to obtain representative cores in rock masses in which recovery isdifficult with normal techniques, and to reveal defects and discontinuities such as jointopenings and fillings, shear zones, and cavities. The method, developed by Dr. ManualRocha of Laboratorio Nacional de Engenheira Civil (LNEC) of Lisbon, can produce coresExploration 111Core barrel headCore barrel Reaming shellCore lifterCoring bitFIGURE 1.79Single-tube core barrel. (Courtesy of Sprague and Henwood, Inc.)Core barrel head Inner tubeOuter tubeReamingshell Core lifterCoring bitFIGURE 1.80Rigid-type double-tube core barrel. (Courtesy of Sprague and Henwood, Inc.)Core barrel headouterHanger bearing assemblyReamingshell Blank bitOutertubeInner tubeInner tubeheadBall bearingsCore lifterPin andnutBearingretainer Lifter baseFIGURE 1.81Swivel-type double-tube core barrel, series M. (Courtesy of Sprague and Henwood, Inc.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 111112 Geotechnical Investigation MethodsRetriever − Lowered onwireline cable − spreads latchand grips retrieving spear forinner tube recoverySimple multifinger springlatch holds inner tube securelyin positionHardened landing seat preventsinner tube from striking the bitOne heavy-duty bearing − designed to take both thrustand hanging loadsCompression spring − transferscore breaking load to the outertube Swivel connection forsurface handlingLocking balls cammed intopositive locking position onthe retrieving spearHeat-treated retrieverlock bodyLatch spreader − opens latchfingers to release inner tubeassemblyCompression spring forceengages locking bulls onretrieving spearJar rod has provision forjarring in both directionsTeflon ringTeflon ringShut-off load cell − providesfor indication of core block andresets automaticallyHardened pump-in washer −opens when inner tube is seated and latchedHardened retrievingspearRetrieverHard surfacingstripsCore lifterGrease fittingBitReversible inner tube −core can be removed fromeither endFIGURE 1.82Wireline core barrel and retrieval assembly. (Courtesy of Sprague and Henwood, Inc.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 112of 100% recovery with the orientation known. Defect orientation is an important factor inrock-mass stability analysis.Technique1. An NX-diameter hole or larger is drilled to where integral coring is to begin.2. A second, smaller hole (nominally about 1 in. [26 mm] in diameter) is drilledcoaxially with the first through the desired core depth, although usually notexceeding 1.5 m in depth.3. A notched pipe is lowered into the hole andbonded to the rock mass withcement or epoxy resin grout, which leaves the pipe through perforations.4. After the grout has set, a core is recovered by overcoring around the pipe andthrough the cemented mass.5. During installation of the pipe, the notch positions are carefully controlled by aspecial adapter and recorded so that when the core is retrieved, the orientationof the fractures and shear zones in the rock mass are known.Large-Diameter Cores by Calyx or Shot DrillingPurposeCalyx or shot drilling is intended to allow borehole inspection in rock masses in holes upto 6 ft (2 m) in diameter.MethodCalyx drilling uses chilled shot as a cutting medium. The shot is fed with water and lodgesaround and partially embeds in a bit of soft steel. The flow of freshwater is regulated carefully to remove the cuttings but not the shot. The cores are recovered by a special core-lifter barrel, wedge pins, or mucking after removal of the core barrel. LimitationsThe method is limited to rock of adequate hardness to resist erosion by the wash water andto vertical or nearly vertical holes.Exploration 113Scribe mark90°�90°αδJoint surfaceFIGURE 1.83Oriented core with the joint surface intersecting the core wall at the jointdip angle. The boundaries of a horizontal line across the joint arelocated at angle ø providing the strike angle. CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 1131.4.6 Sample and Core TreatmentUpon RetrievalThe sampler is dismantled carefully to avoid shocks and blows (in soils), obvious cut-tings are removed, and the recovery is recorded (RQD is also recorded in rock masses).114 Geotechnical Investigation MethodsFIGURE 1.84Massive, hard granite gneiss at the mouth of a water tunnel. Note diorite dike and seepage from joints. Corerecovery in such materials should be high.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 114The sample is immediately described and logged. It is not allowed to dry out, since theconsistency of cohesive soils changes and details of stratification become obscured. Thesample is then preserved and protected from excessive heat and freezing. Exploration 115FIGURE 1.85Jointed granite gneiss and crushed rock zone at other end of tunnel of Figure 1.84 about 400 m distant. Corerecovery is shown in Figure 1.86.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 115Preservation, Shipment and StorageSplit-Barrel SamplesCarefully place intact uncontaminated short cores in wide-mouth jars of sufficient size (16 oz)to store 12 in. of sample. The samples, which may be used for laboratory examination, shouldnot be mashed or pushed into any container; such action would result in complete loss offabric and structure. The jar caps should contain a rubber seal, be closed tightly, and be waxedto prevent moisture loss. Liner samples are preserved as thin-wall tube samples.Thin-Wall Tube SamplesRemove all cuttings from the sample top with a small auger and fill the top with a mixtureof paraffin and a microcrystalline wax such as Petrowax, applied at a temperature close tothe congealing point. Normal paraffin is subjected to excessive shrinkage during coolingand should not be used or an ineffective moisture seal will result. The top is capped, taped,and waxed.Invert the tube, remove a small amount of soil from the bottom and fill the tube withwax. Cap, tape, and wax the bottom.Tubes should be shipped upright, if possible, in containers separating the tubes fromeach other and packed with straw.In the laboratory, tubes that are not to be immediately tested are stored in rooms with con-trolled humidity to prevent long-term drying. Soil properties can change with time; there-fore, for best results, samples should be tested as soon as they are received in the laboratory.Rock CoresRock cores are stored in specially made boxes (Figure 1.86) in which wooden spacers areplaced along the core to identify the depth of run.Extrusion of UD SamplesThin-Wall Pushed SamplesTo obtain specimens for testing thin-wall tube, samples should be extruded from the tubein the laboratory in the same direction as the sample entered the tube, with the tube held116 Geotechnical Investigation MethodsFIGURE 1.86Core recovery of about 90% in fractured diorite grading to gneiss; RQD about 40 to 70%. Coring with NXdouble-tube swivel-type barrel.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 116vertical, as shown in Figure 1.87. This procedure avoids the effects on sample quality ofreverse wall friction and of the sample’s passing the cutting edge of the tube.Thin-Wall Cored SamplesBecause they contain strong cohesive soils, wall friction in cored soil samples is usually toohigh to permit extrusion from the entire tube without causing severe disturbance. Removalnormally requires cutting the tube into sections and then extruding the shorter lengths.Exploration 117FIGURE 1.87Vertical extrusion of Shelby tube sample in the same direction as taken in the field to minimize disturbance.(Courtesy of Joseph S. Ward and Assoc.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 117Field ExtrusionSome practitioners extrude the sample in the field, cutting off 6-in. sections, wrappingthem in aluminum foil, and surrounding them with wax in a carton. The procedure sim-plifies transport, but leads to additional field and laboratory handling which may result inthe disturbance of easily remolded soils.118 Geotechnical Investigation Methods4540353025N201510510zpzp505540PropertylineLegend21/2 in. diameter exploratory boringGeology legendgn − shallow rock, gneissRm − residual soilOs − soft organic alluviumExisting wellTest pit for compaction sampleSectionsScale in meters0 10 20 30Test Pit and BoringLocation PlanFIGURE 1.88Example of test pit and boring location plan using topographic map and engineering geology map as basemap. (Courtesy of Joseph S. Ward and Assoc.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 1181.4.7 Data PresentationBasic ElementsLocation PlanLocations of all explorations should be shown accurately on a plan. It is helpful to use a topographic map as a base map, which also shows the surficial geology as in Figure 1.88.A map providing the general site location is also useful, especially for future referenceto local geologic conditions. Many reports lack an accurate description of the sitelocation.Geologic SectionsData from the various exploration methods are used as a basis for typical geologic sec-tions to illustrate the more significant geologic conditions, as in Figure 1.89. The objectiveis to illustrate clearly the problems of the geologic environment influencing design andconstruction. For engineering evaluations, it is often useful to prepare large-scale sections on whichare plotted all of the key engineering property data as measured in the field and in the lab-oratory.Fence diagrams, or three-dimensional sections, are helpful for sites with complex geol-ogy. An example is given in Figure 1.90.LogsThe results of test and core borings, test pits, and other reconnaissance methods are pre-sented on logs which include all pertinent information.Exploration 119Elevation (m)−20−15−10−50+5+10+156 7 45 46 21 20 27−20−15−10−50+5+10+15Section A-AHorizontal scale (m)0 10 20 30GWLKey to boringFinal gradeSoftFirm2.3.1.1.3.2.21 17 5012 20 22 25 14 13 7 11 12 12 7 12 13 20 20 21 16 27 1014 27 28 24 16 6 6 12 12 6 13 8 10 10 11 18 27 11 20 15 180 0 0 1 4 4 9 220 1 028 22 9 5Numbers to the right of boring indicatenumber of blows required by a 65-kg hammer falling 75 m to drive a 5-cm O.D. sampling spoon to 30 cm (Approximately equivalent to understand penetration resistance.)3 5 94 3 2 2 8 12 15 18 20 12 21 29 22 30 5050 5010 6 10 8 4 6 7 13 26 20 12 23 19 26 14 23 32 504 16 15 24 20 30 22 23 19 14 11 13 15 22 18 21 22 16 26 3234FIGURE 1.89Typical geologic section across site shown in stratum descriptions in Figure 1.88: (1) recent alluvium marinedeposits consisting of interbedded organic silts, sands, and clays; (2) residual soil: silt, clay, and sand mixtures;(3) micaceous saprolite: highly decomposed gneiss retaining relict structure; (4) weathered and partiallydecomposed gneiss. (Courtesy of Joseph S. Ward and Assoc.)CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 119120 Geotechnical Investigation Methods6 12 6 3 2 2 1 5 21 C9 10 11 2 0 3 36 C9 10 11 2 0 3 36 C5 8 4 24 9 12 1830 11 20 C29 C9 10 6 7 10 12 C2 11 21 30 11 20 C17 16 33 27 29 CRsRsRsRsCs5 8 4 2 19 30 C4 9 12 18 CAsAsAsAoAsAsAsAoRsRdecRdecRdecRdecNNNN+3 mTB4TB3TB2TB1TB6TB7TB8TB3TB7TB6(a)(b)NNDesigner'sbuilding levelLegend:N − blows, SPTTP − test boring number − GWLAs − alluvial sandsAo − organic soilsRs − residual soilsCs − colluvial soilsRdec − decomposed rockGn − sound gneissC − coredScale: H = VSite preparationlevel + 3 m+ 6 m+ 10 m+ 3 m+ 3 mPossibleexcavationlevels− 3 m30 mNRs50 m+10 m−3 m30 m+6mGnGnGn50 mFIGURE 1.90Geologic diagrams illustrate conditions at and below the building level proposed by the designer for a Class Istructure in a nuclear power plant complex where support on material of only one type is required. Thediagrams show clearly the conditions for foundations and for excavation support. To reach decomposed rock amaximum excavation of 13 m is required and to reach sound rock, 15 m. Backfill would be controlled fill orrollcrete depending on requirements of the licensing agency. (a) Geologic conditions; (b) geologic conditions atdesigner’s building level.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 120Boring LogsGeneralLogs are prepared to provide complete documentation on the drilling, sampling, and cor-ing operations and on the materials and other aspects of the subsurface encountered,including groundwater conditions. They provide the basis for analysis and design, and therefore complete documentation and clear and precise presentation of all data arenecessary. Normally, two sets of logs are required: field logs and report logs, each servinga different purpose.Field LogA field log is intended to record all of the basic data and significant information regardingthe boring operation. Typical contents are indicated in the example given in Figure 1.91,which is quite detailed, including the sample description and remarks on the drilling oper-ations. The field log is designed to describe each sample in detail as well as other condi-tions encountered. All of the information is necessary for the engineer to evaluate thevalidity of the data obtained, but it is not necessary for design analysis.Exploration 121FIGURE 1.91Example of a field test boring log for soil and rock drilling.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 121Report LogA preliminary report log is begun by the field inspector as the field boring log is prepared.The report log is intended to record the boring data needed for design analysis as well assome laboratory identification test data and a notation of the various tests performed. Thereport log also allows changes to be made in the material description column so that thedescriptions agree with gradation and plasticity test results from the laboratory. The exam-ples given in Figure 1.92 (test boring report log) for a soil and rock borehole and Figure 1.93(core boring report log) for rock core borings illustrate the basic information required forreport logs.122 Geotechnical Investigation MethodsFIGURE 1.92Example of test boring log for soil and rock boring.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 122ReferencesASCE, Geophysical Exploration for Engineering and Environmental Investigations, TechnicalEngineering and Design Guides as adapted from the US Army Corps of Engineers, No. 23, 1998.ASP, Manual of Photo Interpretation, American Society of Photogrammetry, Washington, DC, 1960.ASTM, Symposium on Surface and Subsurface Reconnaissance, Spec. Pub. No. 122, American Societyfor Testing and Materials, Philadelphia, June 1951.Auld, B., Cross-hole and down-hole vs by mechanical impulse, Proc. ASCE J. Geotech. Eng. Div., 103,1381–1398, 1977.Avery, T.E. and Berlin, G.L., Fundamentals of Remote Sensing and Airphoto Interpretation, 5th ed.,Macmillan, New York, 1992.Ballard, R. F., Jr., Method for crosshole seismic testing, Proc. ASCE J. Geotech. Eng. Div., 102,1261–1273, 1976.Belcher, D. J., The Engineering Significance of Landforms, Pub. No. 13, Highway Research Board,Washington, DC, 1948.Broms, B. B., Soil sampling in Europe: state-of-the art, Proc. ASCE J. Geotech. Eng. Div., 106, 65–98, 1980.Exploration 123FIGURE 1.93Example of a report log for rock-core boring.CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 123Civil Engineering, Directional Drill Scouts Water Tunnel’s Path, Civil Engr, ASCE, Apr. 1998.Cotecchia, V., Systematic Reconnaissance Mapping and Registration of Slope Movements, Bull. No.17, IntI. Assoc. Eng. Geol., June 1978, pp. 537.Dahlin, T., Bjelm, L., and Svennsson, C., Resistivity Pre-Investigations for the Railway Tunnelthrough Hallandsas Sweden, Proceedings of the 2nd European EEDS Meeting, Nantes, France,2–4 Sept., 1996, pp. 109–112.Dobecki, T. L., Measurements of Insitu Dynamic Properties in Relation to Geologic Conditions,Geology in the Siting of Nuclear Power Plants, Reviews in Engineering Geology IV, The GeologicalSociety of America, Boulder, CO, 1979, pp. 201–225.Eide, O., Marine Soil Mechanics-Applications to North Sea Offshore Structures, Pub. No. 103,Norwegian Geotechnical Institute, Oslo, 1974, p. 19.ENR, Soil Sampling Techniques, Engineering News-Record, Apr. 24, 1952.ENR, Impact Drill Drives through Hard Rock Fast, Engineering News-Record, Nov. 3, 1977, p. 14.Deere, D. U., Technical description of rock cores for engineering purposes, Rock Mech. Eng. Geol., 1,18–22, 1963.DeLoach, S.R. and Leonard, J., Making Photographic History, Professional Surveyor, Apr. 2000.Ghatge, S.L., Microgravity method for detection of abandoned mines in New Jersey, Bull. Assoc. ofEng. Geologists, 30, 79–85, 1993.Gillbeaut, J.C., Lidar: Mapping a Shoreline by Laser Light, Geotimes, November 2003.Greenfield, R. J., Review of geophysical approaches to the detection of Karst, Bull. Assoc. Eng. Geol.,16, 393–408, 1979.Griffiths, D. H. and King, R. F., Applied Geophysics for Engineers and Geologists, Pergamon Press,London, 1969.Henderson III, F.B., Remote Sensing for Acid Mine Sites, Geotimes, November 2000.Hryciw, R.D., Raschke, S.A., Ghalib, A.M., and Shin, S., A Cone With a View: The VisCPT, Geo-Strata,Geo-Institute, ASCE, July 2002.Ladd, J. W., Buffler, R. T., Watkins, J. S., Worzel, J. L., and Carranza, A., Deep Seismic ReflectionResults from the Gulf of Mexico, Geology, Geological Society of America, Vol. 4, No. 6, 1976,pp. 365–368.Lueder, D. R., Aerial Photographic Interpretation: Principles and Applications, McGraw-Hill, New York,1959.Mooney, H. M., Handbook of Engineering Seismology, Bison Instruments Inc., Minneapolis, MN, 1973.Myung, J. T. and Baltosser, R. W., Fracture Evaluation by the Borehole Logging Method, Stability ofRock Slopes, ASCE, New York, 1972, pp. 31–56.Professional Surveyor, Vol. 19, October 1999.Professional Surveyor, Component-built Aerial Sensor Means Imagery for Everyone, October 2002.Robertson, P.K., Campanella, R.G., Gillespe, D., and Grieg, J., Use of piezometer cone data,Proceedings In-Situ ’86, ASCE Special Conference, Blacksburg, VA, 1986.Robertson, P.K.,Seismic Cone Penetration for Evaluating Liquefaction Potential, Conference on RecentAdvances in Earthquake Design Using Laboratory and In-situ Tests, Seminar Sponsored byConeTec Investigations, Ltd., Feb. 5, 1990.Robertson, P.K., Soil classification using the cone penetration test, Can. Geotech. J., 27, 151–158, 1990.Robertson, P.K., Lunne, T., and Powell, J.J.M., Geo-environmental applications of penetration testing,in Geotechnical Site Characterization, Robertson, P. K. and Mayne, R., Eds., Balkema, Rotterdam,1998, pp. 35–48.Rogers, F. C., Engineering Soil Survey of New Jersey, Report No. 1, Engineering Research BulletinNo. 15, College of Engineering, Rutgers Univ., Edwards Bros. Inc., Ann Arbor, MI, 1950.Sanglerat, G., The Penetrometer and Soil Exploration, Elsevier, Amsterdam, 1972, p. 464.Schmertmann, J. H., Guidelines for CPT Performance and Design, U.S. Dept. of Transportation,Federal Highway Admin., Offices of Research and Development, Washington, DC, 1977.USACE, Engineering and Design — Soil Sampling, U.S. Army Corps of Engrs Pub. No. EM 1110-1-1906, 1996, 10–19, 10–25.USBR, Earth Manual, U.S. Bureau of Reclamation, Denver, CO, 1974.Way, D. S., Terrain Analysis, 2nd ed., Dowden, Hutchinson & Ross, Stroudsburg, PA, 1978.124 Geotechnical Investigation MethodsCRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 124Further ReadingCook, J. C., Status of Ground Probing Radar and Some Recent Experience, Subsurface Exploration forUnderground Excavation and Heavy Construction, Proc. ASCE, New York, 1974, pp. 175–194.Godfrey, K. A., Jr., What Future for Remote Sensing in Space, Civil Engineering, ASCE, July, 1979, pp. 61–65.Hvorslev, J. J., Subsurface Exploration and Sampling of Soils for Civil Engineering Purposes, WaterwaysExperimental Station, U.S. Army Engineers, Vicksburg, MS, November 1949.Lowe III, J. and Zaccheo, P. F., Subsurface explorations and sampling, Foundation EngineeringHandbook, Winterkorn, H. F. and Fang, H.-Y., Eds., Van Nostrand Reinhold Co., New York,1975, chap. 1, pp. 1–66.Lundstrom, R. and Stanberg, R., Soil-Rock Drilling and Rock Locating by Rock Indicator, Proceedingsof the 6th International Conference on Soil Mechanics and Foundation Engineering, Montreal, 1965.McEldowney, R. C. and Pascucci, R. F., Applications of Remote-sensing Data to Nuclear Power PlantSite Investigations, Geology in the Siting of Nuclear Power Plants, Reviews in Engineering GeologyIV, The Geological Society of America, Boulder, CO, 1979, pp. 121–139.Moffatt, B. T., Subsurface Video Pulse Radars, Subsurface Exploration for Underground Excavation andConstruction, Proc. ASCE, New York, 1974, pp. 195–212.Morey, R. M., Continuous Subsurface Profiling by Impulse Radar, Subsurface Exploration inUnderground Excavation and Heavy Construction, Proceedings of the ASCE, New York, 1974, pp.213–232.Underwood, L. B., Exploration and Geologic Prediction for Underground Works, SubsurfaceExploration for Underground Excavation and Heavy Construction, ASCE, New York, 1974, pp.65–83.USDA, Soil Survey of Autauga County, Alabama, U.S. Dept. of Agriculture, Soil ConservationService, 1977, 64 pp. and maps.Exploration 125CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 125CRC_42742_Ch001.qxd 9/21/2006 5:38 PM Page 1262Measurement of Properties2.1 Introduction2.1.1 ObjectivesThe properties of geologic materials are measured to provide the basis for:1. Identification and classification.2. Correlations between properties including measurements made during otherinvestigations in similar materials.3. Engineering analysis and evaluations.2.1.2 Geotechnical PropertiesBasic PropertiesBasic properties include the fundamental characteristics of the materials and provide abasis for identification and correlations. Some are used in engineering calculations.Index PropertiesIndex properties define certain physical characteristics used basically for classifications,and also for correlations with engineering properties.Hydraulic PropertiesHydraulic properties, expressed in terms of permeability, are engineering properties. Theyconcern the flow of fluids through geologic media.Mechanical PropertiesRupture strength and deformation characteristics are mechanical properties. They are alsoengineering properties, and are grouped as static or dynamic.CorrelationsMeasurements of hydraulic and mechanical properties, which provide the basis for all engi-neering analyses, are often costly or difficult to obtain with reliable accuracy. Correlationsbased on basic or index properties, with data obtained from other investigations in which127CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 127extensive testing was employed or engineering properties were evaluated by back-analysisof failures, provide data for preliminary engineering studies as well as a check on the rea-sonableness of data obtained during investigation.Data on typical basic, index, and engineering properties are given throughout the bookfor general reference. A summation of the tables and figures providing these data is givenin Appendix E.2.1.3 Testing Methods SummarizedGeneralA general summary of the significant basic, index, and engineering properties of soil androck, and an indication of whether they are measured in the laboratory, in situ, or both, isgiven in Table 2.1.128 Geotechnical Investigation MethodsTABLE 2.1Measurement of Geotechnical Properties of Rock and SoilLaboratory Test In SituProperty Rock Soil Rock Soil(a) Basic PropertiesSpecific gravity X XPorosity X XVoid ratio XMoisture content X X X XDensity X X X XNatural X XMaximum XMinimum XRelative X XOptimum moisture density XHardness XDurability XReactivity X XSonic-wave characteristics X X X X(b) Index PropertiesGrain-size distribution XLiquid limit XPlastic limit XPlasticity index XShrinkage limit XOrganic content XUniaxial compression XPoint-load index X(c) Engineering PropertiesPermeability X X X XDeformation moduli: static or dynamic X X X XConsolidation X XExpansion X X X XExtension strain X XStrengthUnconfined X XConfinedStatic X X X XDynamic XCalifornia bearing ratio (CBR) X XCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 128Laboratory TestingSoil samples and rock cores are, for the most part tested in the laboratory. Rock cores areoccasionally field tested.Rock cores are tested in the laboratory primarily for basic and index properties, sinceengineering properties of significance are not usually represented by an intact specimen.Laboratory tests of intact specimens, the property measured, and the application of thetest in terms of the data obtained are summarized in Table 2.2.Soil samples are tested for basic and index properties and for engineering propertieswhen high-quality undisturbed samples are obtained (generally limited to soft to hardintact specimens of cohesive soils lacking gravel size or larger particles). Laboratory soiltests, properties measured, and the application of the tests in terms of the data obtainedare summarized in Table 2.3.In Situ TestingGeologic formations are tested in situ within boreholes, on the surface of the ground, orwithin an excavation.Measurement of Properties 129TABLE 2.2 Intact Rock Specimens: Laboratory TestingProperty or Test Applications SectionBasic Properties Correlations, analysisSpecific gravity Mineral Identification 2.2.1Porosity Property correlations 2.2.1Density Material and property correlations 2.2.1Engineering analysisHardness Material correlations 2.2.1Tunneling machine excavation evaluationDurabilityLA abrasion Evaluation of construction aggregate 2.2.1qualityBritish crushingReactivity Reaction between cement and aggregate 2.2.1Sonic velocities Computations of dynamic properties 2.5.3Index Properties Classification and correlationsUniaxial compression See rupture strength 2.4.3Point-load test See rupture strength 2.4.3Permeability Not normallyperformed in the labRupture Strength Measurements ofTriaxial shear Peak drained or undrained strength 2.4.3Unconfined compression Unconfined (uniaxial) compressive 2.4.3strength used for correlationsPoint-load test Tensile strength for correlation with 2.4.3uniaxial compressionUniaxial tensile strength Strength in tension 2.4.3Flexural or beam strength Strength in bending 2.4.3Deformation (static) Measurements ofTriaxial test Deformation moduli Ei, Es, Et 2.4.3Unconfined compression Deformation moduli Ei, Es, Et 2.4.3Dynamic Properties Measurements ofResonant column Compression and shear wave velocities 2.5.3Vp, VsDynamic moduli E, G, DCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 129130 Geotechnical Investigation MethodsTABLE 2.3 Soils: Laboratory TestingProperty or Test Applications SectionBasic Properties Correlations, classificationSpecific gravity Material identification 2.2.3Void ratio computationMoisture or water content Material correlations in the natural state 2.2.3Computations of dry densityComputations of Atterberg limitsDensity: natural (unit weight) Material correlations 2.2.3Engineering analysisDensity: maximum Relative density computations 2.2.3Moisture–density relationshipsDensity: minimum Relative density computations 2.2.3Optimum-moisture density Moisture–density relationships for field 2.2.3compaction controlSonic velocities Computations of dynamic properties 2.5.3Index Properties Correlations, classificationGradation Material classification 2.2.3Property correlationsLiquid limit Computation of plasticity index 2.2.3Material classificationProperty correlationsPlastic limit Computation of plasticity index 2.2.3Shrinkage limit Material correlations 2.2.3Organic content Material classification 2.2.3Permeability Measurements of k inConstant head Free-draining soil 2.3.3Falling head Slow-draining soil 2.3.3Consolidometer Very slow draining soil (clays) 2.5.4Rupture Strength Measurements ofTriaxial shear (compression or Peak undrained strengh sa, cohesive soils 2.4.4extension) (UU test)Peak drained strength, φ, c, φ_, c_, all soilsDirect shear Peak drained strength parameters 2.4.4Ultimate drained strength φ_r cohesive soilsSimple shear Undrained and drained parameters 2.4.4Unconfined compression Unconfined compressive strength for 2.4.4cohesive soilsApproximately equals 2saVane shear Undrained strength sa for clays 2.4.4Ultimate undrained strengths srTorvane Undrained strengths sa 2.4.4Ultimate undrained strength sr (estimate)Pocket penetrometer Unconfined compressive strength 2.4.4(estimate)California bearing ratio CBR value for pavement design 2.4.4Deformation (static) Measurements ofConsolidation test Compression vs. load and time in clay soil 2.5.4Triaxial shear test Static deformation moduli 2.5.4Expansion test Swell pressures and volume change 2.5.4in the consolidometerDynamic PropertiesCyclic triaxial Low-frequency measurements of dynamic 2.5.5moduli (E, G, D), stress vs. strain andstrength 2.4.4(Continued)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 130Rock masses are usually tested in situ to measure their engineering properties, as well astheir basic properties. In situ tests in rock masses, their applications, and their limitationsare summarized in Table 2.4.Soils are tested in situ to obtain measures of engineering properties to supplement labo-ratory data, and in conditions where undisturbed sampling is difficult or not practicalsuch as with highly organic materials, cohesionless granular soils, fissured clays, andcohesive soils with large granular particles (such as glacial till and residual soils). In situsoil tests, properties measured, applications, and limitations are summarized in Table 2.5.Measurement of Properties 131TABLE 2.3 (Continued)Property or Test Applications SectionCyclic torsion Low-frequency measurements of dynamic 2.5.5moduli, stress vs. strainCyclic simple shear Low-frequency measurements of dynamic 2.5.5moduli, stress vs. strain and strength 2.4.4Ultrasonic device High-frequency measurements of 2.5.5compression- and shear-wave velocities Vp, VsResonant column device High-frequency measurements of 2.5.5compression and shear-wave velocities andthe dynamic moduliTABLE 2.4 Rock Masses — In Situ TestingCategory — Tool or Method Applications Limitations SectionBasic Properties 1.3.6Gamma–gamma Continuous measure Density measurementsborehole probe of densityNeutron borehole probe Continuous measure of moisture Moisture measurements 1.3.6Index PropertiesRock coring Measures the RQD (rock Values very dependent on 1.4.5quality designation) used drilling equipment andfor various empirical techniquescorrelationsSeismic refraction Estimates rippability on the basis Empirical correlations. 1.3.2of P-wave velocities Rippability depends on equipment usedPermeabilityConstant-bead test In boreholes to measure k in Free-draining materials 2.3.4heavily jointed rock masses. Requires ground saturationFalling-head test In boreholes to measure k in Slower draining materials 2.3.4jointed rock masses. Can be or below water tableperformed to measure kmean, kv, or khRising-head test Same as for falling-head test Same as for falling-head test 2.3.4Pumping tests In wells to determine kmean in Not representative for 2.3.4saturated uniform formations. stratified formations. Measures average k forentire mass(Continued)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 131132 Geotechnical Investigation MethodsTABLE 2.4 Rock Masses — In Situ Testing (Continued)Category — Tool or Method Applications Limitations SectionPressure testing Measures kh in vertical borehole Requires clean borehole 2.3.4walls Pressures can cause joints to open or to clogfrom migration of finesShear StrengthDirect shear box Measures strength parameters Sawing block specimen 2.4.3along weakness planes of and test setup costly. rock block A surface test. Several tests required for Mohr’senvelopeTriaxial or uniaxial Measures triaxial or uniaxial Same as for direct shear box 2.4.3compression compressive strength ofrock blockBorehole shear device Measures φ and cc in borehole 2.4.3Dilatometer or Goodman Measures limiting pressure See Dilatometer under 2.5.3jack PL in borehole Deformation. Limited by rock-mass strengthDeformation Moduli (Static)Dilatometer or Goodman Measures E in lateral direction Modulus values valid for 2.5.3jack linear portion of load–deformation curve. Resultsaffected by borehole roughness and layeringLarge-scale foundation- Measures E under footings or Costly and time-consuming 2.5.4load test bored piles. Measures shaftfriction of bored pilesPlate-jack test Measures E: primarily used for Requires excavation and 2.5.3tunnels and heavy structures heavy reaction or adit. Stressed zone limited by plate diameter and disturbed by test preparationFlat-jack test Measures E or residual stresses Stressed zone limited by 2.5.3in a slot cut into the rock plate diameter. Test areadisturbed in preparation.Requires orientation in same direction as applied construction stressesRadial jacking tests Measures E for tunnels. Very costly and time- 2.5.3(pressure tunnels) Data most representative of consuming and data in situ rock tests and difficult to interpret. usually yields the Preparation disturbshighest values for E rock massTriaxial compression test Measures E of rock block Costly and difficult to set up. 2.5.3Disturbs rock mass during preparationDynamic PropertiesSeismic direct methods Obtain dynamic elastic moduli Very low strain levels yield 2.5.3E, G, K, and v in boreholes values higher than static moduli(Continued)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 132Measurement of Properties 133TABLE 2.4 (Continued)Category — Tool or Method Applications Limitations Section3-D velocity logger Measures velocity of shearand Penetrates to shallow 2.5.3compression waves (Vs , Vp) depth in boreholefrom which moduli arecomputed. Borehole testVibration monitor Measure peak particle velocity, Surface measurements, 3.2.5or frequency, acceleration, and low-energy leveldisplacement for monitoringvibrations from blasting, traffic, etc.TABLE 2.5 SOILS — In Situ TestingCategory Test or Method Applications Limitations SectionBasic PropertiesGamma-gamma borehole Continuous measure of density Density measurements 1.3.6probeNeutron borehole probe Continuous measure of moisture Moisture-content measures 1.3.6contentSand-cone density Measure surface density Density at surface 2.2.3apparatusBalloon apparatus Measure density at surface Density at surface 2.2.3Nuclear density moisture Surface measurements of Moisture and density at surface 2.2.3meter density and moisturePermeabilityConstant-head test In boreholes or pits to measure Free-draining soils requires 2.3.4k in free-draining soils ground saturationFalling-head test In boreholes in slow-draining Slow-draining materials 2.3.4materials, or materials below or below water tableGWL. Can be performed to measure kmean , kv, or khRising-head test Similar to falling-head test Similar to falling-head test 2.3.4Pumping tests In wells To measure kmean Results not representative 2.3.4in saturated uniform soils in stratified formationsShear Strength (Direct Methods)Vane shear apparatus Measure undrained strength Not performed in sands or 2.4.4su and remolded strength strong cohesive soils affectedsr in soft to firm cohesive soils by soil anisotropy and in a test boring construction time-rate differencesPocket penetrometer Measures approximate Uc in Not suitable in granular soils 2.4.4tube samples, test pits in cohesive soilsTorvane Measures sa in tube samples Not suitable in sands and 2.4.4and pits strong cohesive soilsShear Strength (Indirect Methods)Static cone penetrometer Cone penetration resistance is Not suitable in very strong soils 2.4.5(CPT) correlated with sa in claysand φ in sands(Continued)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 133134 Geotechnical Investigation MethodsTABLE 2.5 SOILS — In Situ Testing (Continued )Category Test or Method Applications Limitations SectionFlat Dilatometer (DMT) Correlations with pressures Not suitable in very strong soils 2.4.5provide estimares of φ and suPressuremeter Undrained strength is found Strongly affected by soil 2.5.4from limiting pressure anisotropycorrelationsCamkometer (self-boring Provides data for determination Affected by soil anisotropy 2.5.4pressuremeter) of shear modulus; shear and smear occurring during strength, pore pressure, installationand lateral stress KoPenetration ResistanceStandard penetration test Correlations provide measures Correlations empirical. Not 2.4.5(SPT) of granular soil DR, φ, E, usually reliable in clay soils.allowable bearing value, and Sensitive to samplingclay soil consistency. Samples proceduresrecoveredStatic cone penetrometer Continuous penetration Samples not recovered, material 2.4.5test (CPT) resistance can provide identification requires boringsmeasures of end bearing and or previous area experienceshaft friction. Correlations provide data similar to SPTCalifornia bearing ratio CBR value for pavement design Correlations are empirical 2.4.5Deformation Moduli (Static)Pressuremeter Measures E in materials Modulus values only valid 2.5.4difficult to sample undisturbed for linear portion of soil such as sands, residual soils, behavior, invalid inglacial till, and soft rock layered formations; notin a test boring used in weak soilsCamkometer See shear strength.Plate-load test Measures modulus of subgrade Stressed zone limited to 2.5.4reaction used in beam-on- about 2 plate diameters. elastic-subgrade Performed in sands andproblems. Surface test overconsolidated claysLateral pile-load test Used to determine horizontal Stressed zone limited to Notmodulus of subgrade about 2 pile diameters. describedreaction Time deformationin clays not consideredFull-scale foundation Obtain E in sands and design Costly and time-consuming 2.5.4load tests parameters for pilesDynamic PropertiesSeismic direct methods Borehole measurements of Very low strain levels yield 1.3.2S-wave velocity to compute values higher than static Ed, Gd, and K moduliSteady-state vibration Surface measurement of shear Small oscillators provide data 2.5.5method wave velocities to obtain only to about 3 m. Rotating Ed, Gd, and K mass oscillator provides greater penetrationVibration monitors Measure peak particle velocity Surface measurements at 3.2.5or frequency, acceleration, and low-energy level for displacement for monitoring vibration studiesvibrations from blasting, traffic, etc.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 134Measurement of Properties 1352.2 Basic and Index Properties2.2.1 Intact RockGeneralTesting is normally performed in the laboratory on a specimen of fresh to slightly weath-ered rock free of defects.Basic properties include volume–weight relationships, hardness (for excavation resist-ance), and durability and reactivity (for aggregate quality).Index tests include the uniaxial compression test (see Section 2.4.3), the point load indextest (see Section 2.4.3), and sonic velocities, that are correlated with field sonic velocities toprovide a measure of rock quality (see Section 2.5.3).Volume–Weight RelationshipsInclude specific gravity, density, and porosity as defined and described in Table 2.6.HardnessGeneralHardness is the ability of a material to resist scratching or abrasion. Correlations can bemade between rock hardness, density, uniaxial compressive strength, and sonic veloci-ties, and between hardness and the rate of advance for tunneling machines and otherTABLE 2.6 Volume–Weight Relationships for Intact Rock SpecimensProperty Symbol Definition Expression UnitsSpecific gravity Gs The ratio of the unit weight of a pure Gs�γm/γw(absolute) mineral substance to the unit weightof water at 4°C. γw � 1g/cm3 or 62.4 pcfSpecific gravity Gs The specific gravity obtained from a mixture Gs � γm/γw(apparent) of minerals composing a rock specimenDensity ρ or γ Weight W per unit volume V of material ρ � W/V t/m3Bulk density ρ Density of rock specimen from field ρ � W/V t/m3(also g/cm3, pcf)Porosity n Ratio of pore or void volume Vv to total n � Vv/Vs %volume Vt.In terms of density and the apparent n � 1�(ρ/Gs) % (metric)specific gravityNotes: Specific Gravities: Most rock-forming minerals range from 2.65 to 2.8, although heavier minerals such ashornblende, augite, or hematite vary from 3 to 5 and higher.Porosity: Depends largely on rock origin. Slowly cooling igneous magma results in relatively nonporous rock,whereas rapid cooling associated with escaping gases yields a porous mass. Sedimentary rocksdepend on amount of cementing materials present and on size, grading, and packing of particles.Density: Densities of fresh, intact rock do not vary greatly unless they contain significant amounts of the heavierminerals.Porosity and density: Typical value ranges are given in Table 2.12.Significance: Permeability of intact rock often related to porosity, although normally the characteristics of the insitu rock govern rock-mass permeability. There are strong correlations between density, porosity, andstrength.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 135excavation methods. The predominant mineral in the rock specimen and the degree ofweathering decomposition are controlling factors.Measurement CriteriaThe following criteria are used to establish hardness values:1. Moh’s system of relative hardness for various minerals.2. Field tests for engineering classification.3. “Total” hardness concept of Deere (1970) based on laboratory tests and devel-oped as an aid in the design of tunnel boringmachines (TBMs). Ranges in totalhardness of common rock types are given in Figure 2.1.4. Testing methods for total hardness (Tarkoy, 1975):136 Geotechnical Investigation MethodsFIGURE 2.1Range of “total” hardness for common rock types. Data are not all inclusive, but represent the range for rockstested in the Rock Mechanics Laboratory, University of Illinois, over recent years. HR � Schmidt hardness; HA� abrasion test hardness. (From Tarkoy, P. J., Proceedings of the 15th Symposium on Rock Mechanics, Custer StatePark, South Dakota, ASCE, New York, 1975, pp. 415–447. With permission.) (a) Inset: Schmidt hammer.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 136Total hardness HT is defined as HT � HR √HA g�1/2 (2.1)where HR is the Schmidt hardness and HA the abrasion test hardness.● Schmidt rebound hardness test: An L-type concrete test hammer (Figure 2.1a), witha spring in tension, impels a known mass onto a plunger held against the speci-men (energy � 0.54 ft lb. or 0.075 m kg). The amount of energy reflected from therock–hammer interface is measured by the amount that the hammer mass iscaused to rebound (ASTM C805).● Shore (C-2) sclerescope is also used to measure rebound hardness. The reboundheight of a small diamond-tipped weight falling vertically down a glass tube ismeasured and compared with the manufacturer’s calibration.● Abrasion hardness test is performed on a thin disk specimen which is rotated aspecific number of times against an abrading wheel, and the weight lossrecorded.DurabilityGeneralDurability is the ability of a material to resist degradation by mechanical or chemicalagents. It is the factor controlling the suitability of rock material used as aggregate for road-way base course, or in asphalt or concrete. The predominant mineral in the specimen, themicrofabric (fractures or fissures), and the decomposition degree are controlling factors.Test MethodsLos Angeles abrasion test (ASTM C535-03 and C131-03): specimen particles of a specified sizeare placed in a rotating steel drum with 12 steel balls (1 7/8 in. in diameter). After rotationfor a specific period, the aggregate particles are weighed and the weight loss comparedwith the original weight to arrive at the LA abrasion value. The maximum acceptableweight loss is usually about 40% for bituminous pavements and 50% for concrete.British crushing test: specimen particles of a specified size are placed in a 4-in.-diametersteel mold and subjected to crushing under a specified static force applied hydraulically.The weight loss during testing is compared with the original weight to arrive at the Britishcrushing value. Examples of acceptable value ranges, which may vary with rock type andspecifying agency, are as follows: particle size (maximum weight loss), 3/4–1 in. (32%),1/2–3/4 in. (30%), 3/8–1/2 in. (28%); and 1/8–3/16 in. (26%).Slake durability test (ASTM D4644): determines the weight loss after alternate cycles ofwetting and drying shale specimens. High values for weight loss indicate that the shale issusceptible to degradation in the field when exposed to weathering processes.Reactivity: Cement–AggregateDescriptionCrushed rock is used as aggregate to manufacture concrete. A reaction between soluble sil-ica in the aggregate and the alkali hydroxides derived from portland cement can produceabnormal expansion and cracking of mortar and concrete, often with severely detrimentaleffects to pavements, foundations, and concrete dams. There is often a time delay of about2 to 3 years after construction, depending upon the aggregate type used.Measurement of Properties 137CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 137138 Geotechnical Investigation MethodsThe ReactionAlkali–aggregate reaction can occur between hardened paste of cements containing morethan 0.6% soda equivalent and any aggregate containing reactive silica. The soda equiva-lent is calculated as the sum of the actual Na2O content and 0.658 times the K2O content ofthe clinker (NCE, 1980). The alkaline hydroxides in the hardened cement paste attack thesilica to form an unlimited-swelling gel that draws in any free water by osmosis andexpands, disrupting the concrete matrix. Expanding solid products of the alkali–silicareaction help to burst the concrete, resulting in characteristic map cracking on the surface.In severe cases, the cracks reach significant widths.Susceptible Rock SilicatesReactive silica occurs as opal or chalcedony in certain cherts and siliceous limestones andas acid and intermediate volcanic glass, cristobolite, and tridymite in volcanic rocks suchas rhyolite, dacites, and andesites, including the tuffs. Synthetic glasses and silica gel arealso reactive. All of these substances are highly siliceous materials that are thermodynam-ically metastable at ordinary temperatures and can also exist in sand and gravel deposits.Additional descriptions are given in Krynine (1957).Reaction ControlReaction can be controlled (Mather, 1956) by:1. Limiting the alkali content of the cement to less than 0.6% soda equivalent. Evenif the aggregate is reactive, expansion and cracking should not result.2. Avoiding reactive aggregate.3. Replacing part of the cement with a very finely ground reactive material (a poz-zolan) so that the first reaction will be between the alkalis and the pozzolan,which will use up the alkalis, spreading the reaction and reaction productsthroughout the concrete.Tests to Determine ReactivityTests include:● The mortar-bar expansion test (ASTM C227-03) made from the proposed aggre-gate and cement materials.● Quick chemical test on the aggregates (ASTM C289-01).● Petrographic examination of aggregates to identify the substances (ASTM C295).2.2.2 Rock MassesGeneralThe rock mass, often referred to as in situ rock, may be described as consisting of rockblocks, ranging from fresh to decomposed, and separated by discontinuities. Mass densityis the basic property. Sonic-wave velocities and the rock quality designation (RQD) areused as index properties.Mass DensityMass density is best measured in situ with the gamma–gamma probe (see Section 1.3.6),which generally allows for weathered zones and the openings of fractures and smallvoids, all serving to reduce the density from fresh rock values.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 138Measurement of Properties 139Rock Quality IndicesSonic wave velocities from seismic direct surveys (see Section 1.3.2) are used in evaluatingrock mass quality and dynamic properties.Rock quality designation may be considered as an index property (see Section 1.4.5).RippabilityRippability refers to the ease of excavation by construction equipment. Since it is relatedto rock quality in terms of hardness and fracture density, which may be measured by seismic refraction surveys (see Section 1.3.2), correlations have been made betweenrippability and seismic P wave velocities as given in Table 2.7. If the material is not rip-pable by a particular piece of equipment, then jack-hammering and blasting arerequired.2.2.3 SoilsGeneralThe basic and index properties of soils are generally considered to include volume–weightand moisture–density relationships, relative density, gradation, plasticity, and organiccontent.Rippable Marginal Non rippableVelocity (m/s × 1000)Velocity (ft/s × 1000)00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 151 2 3 4Rippability based on caterpillar D9 with mounted hydraulic No.9 ripperTopsoilClayGlacial tillIgneous rocksGraniteBasaltTrap rockSedimentary rocksShaleSandstoneSiltstoneClaystoneConglomerateBrecciaCalicheLimestoneMetamorphic rocksSchistSlateMinerals and oresCoalIron oreTABLE 2.7Rock Rippability as Related to Seismic p-Wave Velocities (Courtesy of Caterpillar Tractor Co.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 139140 Geotechnical Investigation MethodsVolume–Weight RelationshipsDefinitions of the variousvolume–weight relationships for soils are given in Table 2.8.Commonly used relationships are void ratio e, soil unit weight (also termed density or massdensity and reported as total or wet density γt, dry density γd, and buoyant density γb),moisture (or water) content w, saturation degree S, and specific gravity Gs of solids.Determinations of basic soil properties are summarized in Table 2.9. A nomograph forthe determination of basic soil properties is given in Figure 2.2.Sand Cone Density Device (Figure 2.3a)A hole 6 in. deep and 6 in. in diameter is dug and the removed material is stored in asealed container. The hole volume is measured with calibrated sand and the density is cal-culated from the weight of the material removed from the hole (ASTM D1556-00).Rubber Balloon DeviceA hole is dug and the material is stored as described above. The hole volume is measuredby a rubber balloon inflated by water contained in a metered tube (ASTM D2167-94).Nuclear Moisture-Density Meter (ASTM D2922)A surface device, the nuclear moisture-density meter, measures wet density from either thedirect transmission or backscatter of gamma rays; and, moisture content from the transmis-sion or backscatter of neutron rays (Figure 2.3b). The manner of measurement is similar tothat of the borehole nuclear probes (see Section 1.3.6). In the direct transmission mode a rodcontaining a Celsium source is lowered into the ground to a desired depth. In the backscat-ter mode, the rod is withdrawn and gamma protons are scattered from the surface contact.A rapid but at times approximate method, measurement with the meter yields satisfactoryresults with modern equipment and is most useful in large projects where soil types used asfills do not vary greatly. Frequent calibration is important to maintain accuracy.Borehole TestsBorehole tests measure natural density and moisture content. Tests using nuclear devicesare described in Section 1.3.6.Moisture content (w)The moisture meter is used in the field (ASTM D4444-92). Calcium carbide mixed with asoil portion in a closed container generates gas, causing pressure that is read on a gage toindicate moisture content. Results are approximate for some clay soils.For cohesive soils, moisture content is most reliably determined by drying in the labo-ratory oven for at least 24 h at 104°C.Moisture–Density Relationships (Soil Compaction)Optimum moisture content and maximum dry density relationships are commonly used tospecify a standard degree of compacting to be achieved during the construction of a load-bearing fill, embankment, earth dam, or pavement. Specification is in terms of a percent ofmaximum dry density, and a range in permissible moisture content is often specified aswell (Figure 2.4).DescriptionThe density of a soil can be increased by compacting with mechanical equipment. If themoisture content is increased in increments, the density will also increase in incrementsCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 140Measurement of Properties 141TABLE 2.8 Volume–Weight Relationships for SoilsaProperty Saturated Unsaturated Illustration of SampleSample (Ws , Ww, Sample (Ws, Ww,Gs, are Known) Gs , V are Known)Volume ComponentsVolume of solids VsVolume of water VwVolume of air or gas Va Zero V�(Vs � Vw)Volume of voids Vv V�Total volume of sample V Vs � Vw MeasuredPorosity n or Void ratio e (Gras)-1Weights for Specific SampleWeight of solids Ws MeasuredWeight of water Ww MeasuredTotal weight of sample Wt Ws � WwWeights for Sample of Unit VolumeDry-unit weight γdWet-unit weight γtSaturated-unit weight γsSubmerged (buoyant) unit γs�γwcweight γbCombined relationsMoisture content wDegree of saturation S 1.00 γd � γs � γd � γw � �Specific gravity Gsa After NAVFAC, Design manual DM-7.1, Soil Mechanics, Foundations and Earth Structures, Naval facilitiesEngineering Command, Alexandria, VA, 1982.b γw is unit weight of water, which equals 62.4 pcf for fresh water and 64 pcf for sea water (1.00 and 1.025 g/cm3).c The actual unit weight of water surrounding the soil is used. In other cases use 62.4 pcf. Values of w and s areused as decimal numbers.Ws�Vsγwe�1�eγt�1 � WVw�VvWw�WsWs � Wwγw��VWs � Ww�Vs � VwWs � Ww�VWs � Ww�Vs � VwWs�VWs � Ww�Vs � VwVv�Vse�1�eVv�VWs�GsγwWw�γwcWw�γwbWs�GsγwbCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 141under a given compactive effort, until eventually a peak or maximum density is achievedfor some particular moisture content. The density thereafter will decrease as the moisturecontent is increased. Plotting the values of w% vs. γt , or w% vs. γd will result in curves sim-ilar to those given in Figure 2.5; 100% saturation is never reached because air remainstrapped in the specimen.Factors Influencing ResultsThe shape of the moisture–density curve varies for different materials. Uniformly gradedcohesionless soils may undergo a decrease in dry density at lower moisture as capillaryforces cause a resistance to compacting or arrangement of soil grains (bulking). As mois-ture is added, a relatively gentle curve with a poorly defined peak is obtained (Figure 2.5).Some clays, silts, and clay–sand mixtures usually have well-defined peaks, whereas low-plasticity clays and well-graded sands usually have gently rounded peaks (Figure 2.6).Optimum moisture and maximum density values will also vary with the compactedenergy (Figure 2.7).Test MethodsStandard compaction test (Proctor Test) (ASTM D698): An energy of 12,400 ft lb is used tocompact 1 ft3 of soil, which is accomplished by compacting three sequential layers with a5 1/2-lb hammer dropped 25 times from a 12-in. height, in a 4-in.-diameter mold with avolume of 1/30 ft3.Modified compaction test (ASTM D1557): An energy of 56,250 ft lb is used to compact 1 ft3 ofsoil, which is accomplished by compacting five sequential layers with a 10 lb hammerdropped 25 times from an 18 in. height in a standard mold. Materials containing signifi-cant amounts of gravel are compacted in a 6-in.-diameter mold (0.075 ft3) by 56 blows oneach of the five layers. Methods are available for correcting densities for large gravel par-ticles removed from the specimen before testing.Relative Density DRRelative density DR refers to an in situ degree of compacting, relating the natural density ofa cohesionless granular soil to its maximum density (the densest state to which a soil canbe compacted, DR � 100%) and the minimum density (the loosest state that dry soil grainscan attain, DR � 0%). The relationship is illustrated in Figure 2.8, which can be used to findDR when γ N (natural density), γD (maximum density), and γL (loose density) are known.DR may be expressed asDR � (1/γL � 1/γN )/ (1/γL � 1/γD ) (2.2)142 Geotechnical Investigation MethodsTABLE 2.9 Determination of Basic Soil PropertiesDeterminationBasic Soil Property Laboratory Test Field TestUnit weight or density, γd, γt, γs, γb Weigh specimens Cone density device Figure 3.3a, ASTM U1556Rubber ballon device, ASTM D2167Nuclear moisture-density meter, ASTM D2922Specific gravity Gs ASTM D854 NoneMoisture content w ASTM D4444 Moisture meterASTM D2922 Nuclear moisture-density meterVoid ratio e Computed from unit dry weight and specific gravityCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 142SignificanceDR is used for classification of the degree of in situ compactness as given in Figure 2.8 or, more commonly, to classify in situ density as follows: very loose (0–15%), loose(15–35%), medium dense (35–65%), dense (65–85%), and very dense (85–100%) (see Table 2.23 for correlations with N values of the Standard Penetration Test (SPT)). Voidratio and unit weight are directly related to DR and gradation characteristics.Permeability, strength, and compressibility are also related directly to DR and gradationcharacteristics.Measurement of Properties 143EXAMPLEGiven : �wef = 123.6 lbs./ ft. Gs = 2.625 � = 20.0%WET DENSITY, �wet, IN LBS. PER CU. FT.� wet / 62.4VOID RATIO, eDRY DENSITY, �d, IN LBS.CU.FT.WATER CONTENT FOR COMPLETE SATURATION, �sat IN %POROSITY, IN %APPARENT SPECIFIC GRAVITY OF SOIL, GsWATER CONTENT, �, IN PERCENT OF DRY WEIGHTFind: �d = Find: e = �wet1+ �123.61 + 0.20103.0 lbs./ft.3(Gs) (62.4)�d�d62.4 (Gs)103.062.4 (265).377 or 37.7%�sat = 0.6052.65.228 or 22.8%Degree of saturation: S = ��sat.200.228= .877 or 87.7%801.31.31.21.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.31.41.5901.6 1001.71.81101201301401502.41.92.32.22.12.02025303540504555%101214161820222426283032343638408070901001101201302.22.12.01.91.81.71.61.5� d / 62.4%1.01.11.21.31.45048464442�wet�de n�sgtGsω45354030252015105122221n = 1 −−1 = 0.605= 1 −−1 =2.552.602.652.702.75(2.65) (62.4)103.0= =eGs====3FIGURE 2.2Nomograph to determine basic soil properties. (From USBR, Earth Manual, U. S. Burean of Reclamation,Denver, CO, 1974. With permission.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 143Measurements of DRLaboratory testing: See ASTM D4254-00 and Burmister (1948). Maximum density is deter-mined by compacting tests as described in the above section, or by vibrator methodswherein the dry material is placed in a small mold in layers and densified with a hand-heldvibrating tool. Minimum density is found by pouring dry sand very lightly with a funnelinto a mold. DR measurements are limited to material with less than about 35% nonplasticsoil passing the No. 200 sieve because fine-grained soils falsely affect the loose density. Amajor problem is that the determination of the natural density of sands cannot be sampledundisturbed. The shear-pin piston (see Section 1.4.2) has been used to obtain values for γN,or borehole logging with the gamma probe is used to obtain values (see Section 1.3.6).Field testing: The SPT and Cone Penetrometer Test (CPT) methods are used to obtain esti-mates of DR.Correlations: Relations such as those given in Figure 2.10 for various gradations may beused for estimating values for γD and γL.144 Geotechnical Investigation MethodsGageGageDetectorsDetectorsPhoton pathsBackscatter ModeDirect TransmissionSurfaceSurfaceSourceSourcePhoton pathsMin = 50mm (2 in.)(a)(b)FIGURE 2.3(a) Sand cone density device being used to measure in situ density of a compacted subgrade test section for anairfield pavement. (b) Nuclear moisture density meter used to measure in situ density.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 144Gradation (Grain Size Distribution)Gradation refers to the distribution of the various grain sizes in a soil specimen plotted asa function of the percent by weight passing a given sieve size (Figure 2.9):● Well-graded — a specimen with a wide range of grain sizes.● Poorly graded — a specimen with a narrow range of grain sizes.● Skip-graded — a specimen lacking a middle range of grain sizes.Measurement of Properties 145Water content (w %)S = 100% (zero air voids)� dFIGURE 2.4The moisture–density relationship. The soil does not becomefully saturated during the compaction test.Water content (w %)Dry� d FIGURE 2.5Typical compaction curve for cohesionless sandsand sandy gravels. (From Foster, C. R., FoundationEngineering, G. A. Leonards, Ed., McGraw-HillBook Co., New York, 1962, pp. 1000–1024. Withpermission. Reprinted with permission of theMcGraw-Hill Companies.)131120114S = 100%15128Water content (w %)� d (pcf)Siltysand(SM)Sandyclay(SC)Low plasticityclay(CL)FIGURE 2.6Typical standard Proctor curves for variousmaterials.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 145146 Geotechnical Investigation MethodsWater content (w %)14 16 22101112117321� d (pcf)S = 100%3. Mod. AASHO − 56 blows,10-lb hammer, 18-in drop, five layers2. Mod. AASHO − 25 blows,10-lb hammer, 18-in drop, five layers1. Std. AASHO − 25 blows,5 1/2-lb hammer, 12-in drop, three layers(All in 6-in molds)FIGURE 2.7Effect of different compactive energies on asilty clay. (After paper presented at AnnualASCE Meeting, January 1950.)908010011012013014015090801001101201301401500 10 20 30 40 50 60 70 80 90100Loose MediumCompact Compact V.C.Relative density, percent DRMaximum Density or Dense State,γDSaturated moisture content. w ′ Percentage of dry weight GS = 267�L-105DR-40%�N-111�D-122403530252015105Minimum density or loose state, �L unit dry weight, lb per cu. ft.FIGURE 2.8Relative density diagram. (From Burmister,D. M., ASTM, Vol. 48, Philadelphia, PA,1948. Copyright ASTM International.Reprinted with permission.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 146Measurement of Properties 147● Coefficient of uniformity Cu — the ratio between the grain diameter at 60% finer tothe grain diameter corresponding to the 10% finer line, orCu � D60/ D10 (2.3)SignificanceGradation relationships are used as the basis for soil classification systems. Gradationcurves from cohesionless granular soils may be used to estimate γD and γL, and, if γN or DRis known, estimates can be made of the void ratio, porosity, internal friction angle, andcoefficient of permeability.Gradation Curve Characteristics (Burmister, 1948, 1949, 1951a) The gradation curves and characteristic shapes, when considering range in sizes, can beused for estimating engineering properties. The range of sizes CR represents fractions of auniform division of the grain size wherein each of the divisions 0.02 to 0.06, 0.06 to 0.02,etc., in Figure 2.9 represents a CR � 1. Curve shapes are defined as L, C, E, D, or S as givenin Figure 2.9 and are characteristic of various types of soil formations as follows:● S shapes are the most common, characteristic of well-sorted (poorly graded)sands deposited by flowing water, wind, or wave action.CR − 2.7CR − 1.7CR − 0.91009080706050403020100200 60 20 6 2 0.6 0.2 0.06 0.02 0.006 0.0020102035503520100TraceTraceLittleLittleSomeSomeAndAndPercentage finer by weightSeries of type S curvesRegularly varyingFineless and rangeof grain sizes3 4 8 16 30 50 100 200 Sieves3/4 3/41−1/2Uniform scale of fractionsGrain size (mm)100500100500100500100500Log of grain size Log of grain sizeBalanceplus and minusarea for upperand lower branch of curveUpper branchLowerType DType EType LType DD10D10D10D10D1010101010Mean slopePercentage finer by weightBoulders cobblesGravel MSand M Clay-soil plasticity and clay-qualitiesNonplasticSlitCCC FFCR CRmm0.020.0762.000.250.5910 30 602.09.523/8 in.25.476.22289 in. 3 in. 1 in. Nos. Sieves(a)(b)+−−−+ ++++−+FIGURE 2.9Distinguishing characteristics of grain size curves: fineness, range of grain sizes, and shape: (a) type S grainsize curves and (b) type of grain size curve. (From Burmister, D. M., ASTM, Vol. 48, Philadelphia, PA, 1948.Copyright ASTM International. Reprinted with permission.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 147● C shapes have a high percentage of coarse and fine particles comparedwith sandparticles and are characteristics of some alluvial valley deposits in an arid cli-mate where the native rocks are quartz-poor.● E and D shapes include a wide range of particle sizes characteristics of glacialtills and residual soils.RelationshipsGeneral relationships among gradation characteristics and maximum compacted densi-ties, minimum densities, and grain angularity are given in Figure 2.10 (note the signifi-cance of grain angularity). Gradation characteristics for soils of various geologic origins,as deposited, are given in Figure 2.11.Test MethodsGradations are determined by sieve analysis (ASTM D422) and hydrometer analysis(ASTM D422), the latter test being performed on material finer than a no. 200 sieve. Forsieve analysis, a specimen of known weight is passed dry through a sequence of sieves ofdecreasing size of openings and the portion retained is weighed, or a specimen of knownweight is washed through a series of sieves and the retained material dried and weighed.The latter procedure is preferred for materials with cohesive portions because dry sievingis not practical and will yield erroneous results as fines clog the sieves.148 Geotechnical Investigation Methods1401501301201101000 1 2 3 4 5 6 7 8 9 10 11 1215102025Saturated moisture content w ′ ( %) of dry weightTypes CCD and LSEDERange of grain sizes Cr, in units of soil fractionsUnits dry weight �s (pcf)reduced to GS = 2.67 basis(b) Approximate Minimum Densities, 0% Dr(c) Approxomate Influence of Grain Shape on DensityDecrease in Density (pcf)Range in grain sizes (Cr ) Coarser soils Finer soilsGrain shape Change in density (pcf)Very angularSubangularRounded or waterworn0.5% mica10 to −150 to normal+2 to +5− 2 to − 51 − 33 − 55 and greater10 2030+2025toto 25to−FIGURE 2.10Maximum compacted densities, approximateminimum densities, and influence of grainshape on density for various gradations.(From Burmister, D. M., ASTM, Vol. 48,Philadelphia, PA, 1948. Reprinted withpermission of the American Society forTesting and Materials.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 148PlasticityDefinitions and RelationshipsAtterberg limits, which include the liquid limit, plastic limit, and the shrinkage limit, areused to define plasticity characteristics of clays and other cohesive materials.Liquid limit (LL) is the moisture content at which a soil passes from the liquid to the plas-tic state as moisture is removed. At the LL, the undrained shear strength su ≈ 0.03 tsf.Plastic limit (PL) is the moisture content at which a soil passes from the plastic to thesemisolid state as moisture is removed.Plasticity index (PI) is defined as PI � LL � PL.Shrinkage limit (SL) is the moisture content at which no more volume change occursupon drying.Activity is the ratio of the PI to the percent by weight finer than 2 µ m (Skempton, 1953)Liquidity index (LI) is used for correlations and is defined asLI � (w � PL)/(LL�PL) � (w � PL)/PI (2.4)SignificanceA plot of PI vs. LL provides the basis for cohesive soil classification as shown on the plas-ticity chart (Figure 2.12). Correlations can be made between test samples and characteris-tic values of natural deposits. For example, predominantly silty soils plot below the A line,and predominantly clayey soils plot above. In general, the higher the value for the PI andLL, the greater is the tendency of a soil to shrink upon drying and swell upon wetting. Therelationship between the natural moisture content and LL and PI is an indication of the soil’s consistency, which is related to strength and compressibility (see Table 2.37). TheMeasurement of Properties 1490 10 20 4030 50 60 70 80 90 1000 10 20 4030 50 60 70 80 90 100Granular alluvial despositsf cf cf cf cf cffccc0.015 0.150.01 0.250.2 0.60.8 0.30.3 0.10.40.07 D50D50D50D50D50D50D50D50 CR − 0.7 to 1.5CR − 0.7 to 2Low velocitiesS typeS typeS typeBeach sand deposits, wave formedGlacial outwashFlat slopes0.25 2.00.400.15Types E,D,and CDMedium compact Compact LooseCMCL_ + _ _ ++Initial-depositional relative density DR (%) Dune sandsQuiet water to very low velocitiesCR − 1.0 to 2.5 S typeCR − 1 to 3Moderate velocitiesS typeCR − 0.7 to 2.5Steep beachCR − 2 to 5Moderate slopes Very compactS typeCR − 0.7 to 2Flat beachcR − 0.7 to 1.5S typeVCfFIGURE 2.11Probable initial depositional relative densitiesproduced by geologic process of granular soilformation as a tentative guide showing dependence ongrain-size parameters, grading-density relations, andgeological processes. (From Burmister, D. M., ASTMSpecial Technical Publication No. 322, 1962a, pp. 67–97.Reprinted with permission of the American Society forTesting and Materials.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 149liquidity index expresses this relationship quantitatively. The controlling factors in the val-ues of PI, PL and LL for a given soil type are the presence of clay mineral, and the per-centages of silt, fine sand, and organic materials.Test MethodsLiquid limit (ASTM D4318-00) is performed in a special device containing a cup that isdropped from a controlled height. A pat of soil (only material passing a no. 40 sieve) ismixed thoroughly with water and placed in the cup, and the surface is smoothed and thengrooved with a special tool. The LL is the moisture content at which 25 blows of the cupare required to close the groove for a length of 1 cm. There are several test variations(Lambe, 1951).Plastic limit (ASTM D4318-00) is the moisture content at which the soil can just be rolledinto a thread 1/8 in. in diameter without breaking.Shrinkage limit (ASTM D427) is performed infrequently. See Lambe (1951) for discussion.Organic ContentGeneralOrganic materials are found as pure organic matter or as mixtures with sand, silt, or clay.Basic and Index PropertiesOrganic content is determined by the loss by ignition test that involves specimen combus-tion at 440°F until constant weight is attained (Arman, 1970). Gradation is determinedafter loss by ignition testing. Plasticity testing (PI and LL) provides an indication oforganic matter as shown in Figure 2.12 (see also ASTM D2914-00).150 Geotechnical Investigation MethodsBentonite(Wyoming)Volcanic clay(Mexico City)Various types of peatOrganic silt and clay(Flushing meadows L.I.)400400 600 8003002002000100Liquid limitExpansive soils5040302020 30 40 50 60 70 80 9010100DiatomaceousearthKaolin and alluvial claysMicaceous siltsMH and OHML and OLLoess"A" lineSodiumMontmorilloniteLL = 300 to 600PI = 250 to 550706050CHGlacial claysRed tropicallaterite claysCLCL- MLLiquid limitPlasticity index (%)Line"A"FIGURE 2.12Plasticity chart for Unified Classification System.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 150Measurement of Properties 1512.3 Hydraulic Properties (Permeability)2.3.1 IntroductionFlow-Through Geologic MaterialsDefinitions and RelationshipsPermeability, the capacity of a material to transmit water, is only summarized in thischapter. Flow through a geologic medium is quantified by a material characteristic termedthe coefficient of permeability k (also known as coefficient of hydraulic conductivity),expressed in terms of Darcy’s law, valid for laminar flow in a saturated, homogeneousmaterial, ask � q/iA (cm/sec) (2.5)where q is the quantity of flow per unit of time (cm3/sec), i the hydraulic gradient, i.e., thehead loss per length of flow h/L (a dimensional number) and, A the area (cm2).Values for k are often given in units other than cm/sec. For example, 1 ft/day � 0.000283� cm/sec; cm/sec � 3528 � ft/day.Secondary permeabilityrefers to the rate of flow through rock masses, as contrasted withthat through intact rock specimens, and is often given in Lugeon units (see Section 2.3.4).Factors Affecting Flow CharacteristicsSoils: In general, gradation, density, porosity, void ratio, saturation degree, and stratifica-tion affect k values in all soils. Additional significant factors are relative density in granu-lar soils and mineralogy and secondary structure in clays.Rocks: k values of intact-rock relate to porosity and saturation degree. k values of in siturock relate to fracture characteristics (concentration, opening width, nature of filling),degree of saturation, and level and nature of imposed stress form (compressive or tensile).Tensile stresses, for example, beneath a concrete dam can cause the opening of joints andfoliations, significantly increasing permeability.Permeability ConsiderationsDeterminations of k valuesk values are often estimated from charts and tables (see Section 2.3.2) or can be measuredin laboratory tests (see Section 2.3.3) or in situ tests (see Section 2.3.4).Applicationsk values as estimated or measured in the laboratory, are used for:● Flow net construction and other analytical methods to calculate flow quantitiesand seepage forces.● Selection of groundwater control methods for surface and underground excavations.● Design of dewatering systems for excavations.● Evaluation of capillary rise and frost susceptibility.● Evaluation of yield of water-supply wells.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 151In situ measurements of k values are made for evaluations of:● Percolation rates for liquid-waste disposal systems.● Necessity for canal linings (as well as for designing linings).● Seepage losses beneath and around dam foundations and abutments.● Seepage losses in underground-cavern storage facilities.● Groundwater control during excavation.Associated Phenomena: Capillary, Piping, and LiquefactionCapillary is the tendency of water to rise in “soil tubes,” or connected voids, to elevationsabove the groundwater table. It provides the moisture that results in heaving of foun-dations and pavements from freezing (frost heave) and swelling of expansive soils.Rating criteria for drainage, capillary, and frost heave in terms of soil type are given inTable 2.10.Piping refers to two phenomena: (1) water seeping through fine-grained soil, erodingthe soil grain by grain and forming tunnels or pipes; and (2) water under pressure flow-ing upward through a granular soil with a head of sufficient magnitude to cause soilgrains to lose contact and capability for support. Also termed boiling or liquefaction,piping is the cause of a “quick” condition (as in quicksand) during which the sand essen-tially liquefies.“Cyclic” liquefaction refers to the complete loss of supporting capacity occurring whendynamic earthquake forces cause a sufficiently large temporary increase in pore pressuresin the mass.2.3.2 Estimating the Permeability Coefficient kGeneralBasisSince k values are a function of basic and index properties, various soil types and forma-tions have characteristic range of values. Many tables and charts have been published byvarious investigators relating k values to geologic conditions, which are based on numer-ous laboratory and field investigations and which may be used for obtaining estimates ofk of sufficient accuracy in many applications.Partial Saturation EffectsIn using tables and charts, one must realize that the values given are usually for saturatedconditions. If partial saturation exists, as often obtained above the groundwater level, thevoids will be clogged with air and permeability may be only 40 to 50% of that for satu-rated conditions.Stratification EffectsIn stratified soils, lenses and layers of fine materials will impede vertical drainage, andhorizontal drainage will be much greater than that in the vertical direction.RelationshipsPermeability characteristics of soils and their methods of measurement are given in Table2.11. Typical permeability coefficients for various conditions are given in the following152 Geotechnical Investigation MethodsCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 152Measurement of Properties 153TABLE 2.10Tentative Criteria for Rating Soils with Regard to Drainage, Capillarity, and Frost Heaving CharacteristicsaFineness“Trace fine sand”“Trace silt”“Little silt”“Some fine silt”“Some clayey silt” identificationb(coarse and fine)“Little clayey silt”(clay soils dominating)(fissured clay soils)Approx. effective size,0.40.20.20.0740.0740.020.020.010.01D10(mm)cDrainageFree drainage underDrainage byDrainage good to fairDrains slowly,Poor to Imperviousgravity excellentgravity goodfair to poorApprox. range of k(cm/s)0.50.100.0200.00100.00020.20.040.0060.00040.0001Deep wellsWell points successful CapillarityNegligibleSlightModerateModerate to highHighApprox. rise in feet, Hc0.51.57.015.01.03.010.025.0Frost heaving susceptibilityNonfrost-heavingSlightModerate toObjectionableObjectionable to objectionablemoderateGroundwater within 6 ft or Hc/2aCriteria for soils in a loose to medium-compact state. From Burmister D.M., ASTM Special Publication, 113, American Society for Testing and Materials, Philadelphia, PA,U.S.A.bFineness classification is in accordance with the ASSE Classification System.cHazen’s D10: The grain size for which 10% of the material is finer.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 153tables: rock and soil formations, Table 2.12; some natural soil formations, Table 2.13; andvarious materials for turbulent and laminar flow, Table 2.14. Values of k for granular soilsin terms of gradation characteristics (D10, CR, curve type) are given in Figures 2.13 and 2.14,with the latter figure giving values in terms of DR. Rock masses: Permeability values for various rock conditions are given in Table 2.12. Auseful chart for estimating the effect of joint spacing and aperture on the hydraulic con-ductivity is given in Figure 2.15.2.3.3 Laboratory TestsTypes and ApplicationsConstant-head tests are used for coarse-grained soils with high permeability. Falling-headtests are used for fine-grained soils with low permeability. Consolidometer tests may be usedfor essentially impervious soils as described in Section 2.5.4.Constant- and Falling-Head TestsThe two types of laboratory permeameters are illustrated in Figure 2.16. In both cases,remolded or undisturbed specimens, completely saturated with gas-free distilled water,are used. Falling head tests on clay specimens are often run in the triaxial compression154 Geotechnical Investigation MethodsTABLE 2.11Permeability Characteristics of Soils and Their Methods of MeasurementaCoefficient of Permeability k (cm/s) (log scale)a After Casagrande, A. and Fadum, R.E., Soil Mechanics Series, Cambridge, MA, 1940 (from Leonards, G.A.,Foundation Engineering, McGraw-Hill Book Co., New York, 1962, ch. 2).Coefficient of permeability k (cm/s) (log scale)102 101 10 10−1 10−2 10−3 10−410−5 10−6 10−7 10−8 10−9Practically imperviousPoor drainageVery fine sands; organic andinorganic silts; mixtures of sand,silt, and clay; glacial tillstratified clay deposits; etc.Good drainageDrainageTypes of soilDirectdeterminationof coefficientof permeabilityIndirectdeterminationof coefficientof permeabilityClean gravel Clean sand andgravel mixturesClean sand "Impervious soils,e.g.,homogeneousclays below zoneof weathering"Impervious soils" which are modified bythe effects of vegetation and weatheringHorizontal capillarity testComputationsfrom grain size distribution, porosity, etc.Constant-head permeameterDirect testing of soil in its original position(e.g. field-pumping tests)Falling-head permeameterComputationsfrom time rate of consoli-dation and rate of pressuredrop at constant volumeCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 154Measurement of Properties 155TABLE 2.12Typical Permeability Coefficients for Rock and Soil Formationsak (cm/s) Intact Rock Porosity n (%) Fractured Rock SoilPractically 10�10 Massive 0.1–0.5 Homogeneous clay impermeable 10�9 low-porosity 0.5–5.0 below 10�8 rocks zone of weathering10�7Low discharge, 10�6 5.0–30.0 Very fine sands, poordrainage 10�5 Weathered organic and 10�4 granite Schist inorganic silts, 10�3 Clay-filled joints mixtures of sand and clay, glacial till stratified clay depositsHigh discharge, 10�2 Jointed rock Clean sand, cleanfree draining 10�1 Open-jointed rock sand and 1.0 Heavily gravel mixtures101 fractured rock Clean gravel102a After Hoek, E. and Bray, J.W., Rock Slope Engineering, Institute of Mining and Metallurgy, London, 1977.SandstoneTABLE 2.13 Permeability Coefficients for Some Natural Soil FormationsaFormation Value of k (cm/s)River Deposits Rhone at Genissiat Up–0.40Small streams, eastern Alps 0.02–0.16Missouri 0.02–0.20Mississippi 0.02–0.12Glacial Deposits Outwash plains 0.05–2.00Esker, Westfield, Mass. 0.01–0.13Delta, Chicopee. Mass. 0.0001–0.015Till Less than 0.0001Wind Deposits Dune sand 0.1–0.3Loess 0.001�Loess loam 0.0001�Lacustrine and Marine Offshore Deposits Very fine uniform sand, Cu � 5 to 2b 0.0001–0.0064Bull’s liver, Sixth Ave, N.Y., Cu � 5 to 2 0.0001–0.0050Bull’s Liver, Brooklyn, Cu � 5 0.00001–0.0001Clay Less than 0.0000001a From Terzaghi, K. and Peck, R.B., Soil Mechanics in Engineering Practice,2nd ed., Wiley, New York, 1967. Reprinted with permission of John Wiley& Sons, Inc.b Cu � uniformity coefficient.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 155156 Geotechnical Investigation MethodsTABLE 2.14 Typical Permeability Coefficients for Various MaterialsaParticle-Size Range“Effective” SizePermeability Coefficient kInchesMillimetersDmaxDminDmaxDminD14, inD15, (mm)ft/yearft/monthcm/secTurbulent FlowDerrick atone1203648100 �106100 �105100One-man stone124630 �10630 �15530Clean, fine to coarse gravel3¼8010½10 �10610 �10510Fine, uniform gravel3/81/1681.81/25 �1065 �1055Very coarse, clean, uniform tend1/81/3230.81/163 �1063 �1053Laminar FlowUniform, coarse sand1/81/6420.50.60.4 �1060.4×1050.4Uniform, medium sand0.50.250.30.1 �1050.1 �1050.1Clean, well-graded sand and gravel100.050.10.01 �1050.01 �1050.01Uniform, fine sand0.250.050.06400040040 �10−4Well-graded, silty sand and gravel50.010.02400404 �10−4Silty sand20.0050.011001010−4Uniform silt0.050.0050.0065050.5 �10−4Sandy clay1.00.0010.00250.50.05 �10−4Silty clay0.050.0010.001510.10.01 �10−4Clay (30–50% clay sizes)0.050.00050.00080.10.010.001 �10−4Colloidal clay (−2µm≤50%)0.0110Å40Å0.00110�410�9aFrom Hough, K.B., Basic Soils Engineering,The Ronald Press, New York, 1957. CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 156device in which the time required for specimen saturation is substantially shortened byapplying backpressure (Section 2.4.4). Constant-Head Test (ASTM 2434)A quantity of water is supplied to the sample, while a constant head is maintained and thedischarge quantity q is measured. From Darcy’s law, k � qL/Ah (2.6)Measurement of Properties 1571.00.10.010.0011.0x10−41.0x10−51.0 0.8 0.6 0.4 0.2 0.1 0.08 0.06 0.04 0.02 0.01 0.006 0.002Effective size D10, mmSoil laboratory test, 1943. Effective size determinedon seperate sample by a sieve analysisTests by kane x two sieve sizesx four sieve sizesM.S. Thesis No. 558 1948Dept. of Civil Engineering, ColumbiaUniversity, New York CityPoor drainage characteristicsFair drainagecharacteristicsFree-draining soilsCoarse Sandmedium FineCoarse siltClay-soil Silt nonplasticPlastic and clay-qualitiesSieve number2006030CR = 0.9 (two sieve sizes)CR = 1.75 (four sieve sizes)No. 200 sieveNote −XXXX+++Coefficient of permeability, K at 40% Relative density (cm/s)0.02 mmFIGURE 2.13Relationships between permeability and Hazen’s effective size Dn, Coefficient of permeability reduced to basisof 40% DR by Figure 2.15. (From Burmister, D. M., ASTM, Vol. 48, Philadelphia, PA, 1948. Reprinted withpermission of the American Society for Testing and Materials.)Size characteristics(See Figure 3.9)D10 CR Type0.8 0.9 S0.4 0.9 S0.29 0.7 S0.12 0.7 S0.11 0.9 S0.15 4.0 E0.08 5.2 D0.023 1.7 S0.021 0.9 S0.007 8.0 L10 20 30 40 60 70 9080 10050Loose Medium Compact Compact V.C.Relative Density, percent, DRCoefficient of permeability, K (cm / sec)1.00.10.010.0011.0x10−51.0x10−61.0x10−4After Kane M.S. Thesis No. 558, 1948Department of Civil EngineeringColumbia UniversityAfter Burmister Soil LaboratoryColumbia University, 1943 FIGURE 2.14Permeability–relative densityrelationships. (From Burmister, D. M.,ASTM, Vol. 48, Philadelphia, PA, 1948.Reprinted with permission of theAmerican Society for Testing andMaterials.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 157Falling-Head TestFlow observations are made on the rate of fall in the standpipe (Figure 2.16b). At time t,the water level drops from h0 to h1, andk � (aL/At1)(ln h0/h1) (2.7)2.3.4 In Situ TestingSeepage Tests in SoilsTests include constant head, falling or variable head, and rising head. They are summa-rized in terms of applicable field conditions, method, and procedure in Table 2.15.158 Geotechnical Investigation Methods10−210−410−610−810−10Hydraulic conductivity K (m/s)Joint aperture e (mm)beK0.50.10.050.01 1.0100 joints/meter10 joints/meter1 joint/meterFIGURE 2.15Effect of joint spacing and aperture onhydraulic conductivity. (From Hock, E.and Bray, J. W., Rock Slope Engineering,Institute of Mining and Metallurgy,London, 1977. With permission.)OverflowScreen ScreenQhAALLqh1hth0at1(a) (b)FIGURE 2.16Two types of laboratory permeameters: (a) constant-head test; (b) falling-head test.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 158Measurement of Properties 159TABLE 2.15 Seepage Tests in SoilsTestField ConditionsMethodProcedureConstant headUnsaturated(a) Shallow-depth small pit, 12 in deep and square1.Uncased holes, backfill with fine gravel or coarsegranular soils(percolation test)(b) Moderate depth, hand-auger hole2.Saturate ground around hole(c) Greater depth, install casing (open-end pipe test)a3.Add metered quantities of water to hole untilquantity decreases to constant value (saturation)4.Continue adding water to maintain constantlevel, recording quantity at 5-min intervals5.Compute kas for laboratory testFalling or variable headBelow GWL, or inPerformed in cased holea1.Fill casing with water and measure rate of fallslow-draining soils2.ComputationsbRising-head testBelow GWLin soilPerformed In cased holea1.Bail water from holeof moderate k2.Record rate of rise in water level until risebecomes negligible3.After testing, sound hole bottom to check forquick condition as evidenced by rise of soil incasing computationsbaTests performed in casing tan have a number of bottom-flow conditions. These are designed according to geologic conditions, to provide measurements of k mean, kv, or kh.●k mean: determined with the casing flush with the end of the borehole in uniform material, or with casing flush on the interface between an impermeable layer over a per-meable layer.●k v: determined with a soil column within the casing, similar to the laboratory test method, in thick, uniform material.●k h: determined by extending an uncased hole some distance below the casing and installing a well-point filter in the extension.bReferences for computations of kwith various boundary conditions:●NAVFAC Desigh Manual DM-7.1 (1982).●Hoek and Bray (1977).●Lowe and Zaccheo (1975).●Cedergren (1967).CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 159Soil Penetration Tests (CPTU, DMT)The piezocone CPT (Sections 1.3.4 and 2.4.5) and the flat dilatometer test (Section 2.4.5)provide estimates of the horizontal coefficient of permeability, kh.Pumping TestsTests are made from gravity wells or artesian wells in soils or rock masses as described inTable 2.16.Pressure Testing in Rock MassesGeneral ProceduresThe general arrangement of equipment is illustrated in Figure 2.17, which shows twopackers in a hole. One of the two general procedures is used, depending on rock quality.The common procedure, used in poor to moderately poor rock with hole collapse prob-lems, involves drilling the hole to some depth and performing the test with a singlepacker. Casing is installed if necessary, and the hole is advanced to the next test depth.The alternate procedure, used in good-quality rock where the hole remains open, involvesdrilling the hole to the final depth, filling it with water, surging it to clean the walls of fines,and then bailing it. Testing proceeds in sections from the bottom–up with two packers.Packer spacing depends on rock conditions and is normally 1, 2, or 3 m, or at times 5 m.The wider spacings are used in good-quality rock and the closer spacings in poor-qualityrock.Testing Procedures1. Expand the packers with air pressure.2. Introduce water under pressure into the hole, first between the packers and thenbelow the lower packer.3. Record elapsed time and volume of water pumped.4. Test at several pressures, usually 15, 30, and 45 psi (1, 2, and 3 tsf) above the nat-ural piezoelectric level (Wu, 1966). To avoid rock-mass deformation, the excess160 Geotechnical Investigation MethodsTABLE 2.16 Pumping TestsTest Field Conditions Method Procedure DisadvantagesGravity well Saturated, uniform Pump installed in Well is pumped at Provides values for soil (unconfined screened and filtered constant rate until kmeanaquifer) well and surrounded cone of drawdown by a pattern of measured in observation observation wells wells has stabilized (recharge equals pumping rate)Gravity well Rock masses Similar to above Similar to above Flow from entire hole measured. Providesan average valueArtesian well Confined aquifer Similar to above Similar to above Provides values for (pervious under kmeankmean in aquiferthick impervious layer)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 160pressure above the natural piezoelectric level should not exceed 1 psi for eachfoot (23 kPa/m) of soil and rock above the upper packer.Data EvaluationCurves of flow vs. pressure are plotted to permit evaluation of changes in the rock massduring testing:● Concave-upward curves indicate that fractures are opening under pressure.● Convex curves indicate that fractures are being clogged (permeability decreasingwith increased pressure).● Linear variation indicates that no change is occurring in the fractures.Approximate values for k are computed from the expressions (USBR, 1974)k � (Q/2πLH)(ln L/r) for L � 10r (2.8)k � (Q/2πLH) sinh�1(L/2r) for 10r � L � r (2.9)where k is the coefficient of permeability, Q the constant flow rate in the hole, L the lengthof the test section, H the differential head on the test section (see explanation below), r thehole radius and sinh-1 the inverse hyperbolic sine.Measurement of Properties 161Gage, air pressureAirsupplyWaterpumpWatermeter Valves PressuregagesAir hoseInner and outer pipesfor water supply(or single pipe forpacker testing only)Drop pipesExpandable rubbersleeve(Packer lengthapproximately 5times boringdiameter)Perforated outer pipeto test betweenpackers(Inner pipe provideswater to testbelow packers)Air hose tolower packerInner pipe(unperforated)to test lowersectionLower testsectionTest sectionLower packerUpper packerFIGURE 2.17Apparatus for determining rock permeabilityin situ using pressure testing between packers.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 161Head losses in the system should be accounted for in determining the value of H. Sincemost head losses occur in the drop pipe, they can be minimized by using as large a diam-eter pipe as practical. Head loss can be estimated from the relationship (Davis et al., 1970)hf � f (L/D)(v2/2g) (2.10)where L is the pipe length, D the pipe diameter, v the flow velocity, g the gravitationalacceleration and f the frictional component (obtained from charts for various pipe diame-ters, materials, and discharges).Lugeon TestIn the Lugeon test, used commonly in Europe, the hole is drilled to test depth and a packerinstalled about 15 ft (5 m) from the bottom. Flow is measured after 5 or 20 min of testunder pressure, and the test is performed under several pressures. The standard meas-urement of pressure is 10 kg/cm2 and the results are given in Lugeon units.Lugeon unit is defined as a flow of 1 l of water/min of boreholelength at a pressure of 10kg/cm2 (1 Lugeon unit is about 10�5 cm/sec).Disadvantages of Pressure TestingValues can be misleading because high pressures cause erosion of fines from fractures aswell as deformation of the rock mass and closure of fractures (Serafin, 1969).Additional ReferencesDick (1975) and Hoek and Bray (1977) provide additional information.2.4 Rupture Strength2.4.1 IntroductionBasic Definitions● Stress (σ) is force P per unit of area, expressed as σ � P/A (2.11)System Equivalent units for stressEnglish 13.9 psi � 2000 psf � 2 ksf � 1 tsf � 1 barMetric 1 kg/cm2 � 10 T/m2 (≈1 tsf)SI 100 kN/m2 � 100 kPa � 0.1 MPa (≈1 tsf)● Strain (ε) is change in length per unit of length caused by stress. It can occur ascompressive or tensile strain. Compressive and tensile strain are expressed as ε � ∆L/L (2.12)● Shear is the displacement of adjacent elements along a plane or curved surface.● Shear strain (ξ) is the angle of displacement between elements during displace-ment.162 Geotechnical Investigation MethodsCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 162● Shear stress (τ) is the stress causing shear.● Shear strength (S or s) is a characteristic value at which a material fails in ruptureor shear under an applied force.● Dilatancy is the tendency of the volume to increase under increasing shear orstress difference.Strength of Geologic MaterialsComponents: Friction and CohesionFriction is a resisting force between two surfaces as illustrated in Figure 2.18. It is often theonly source of strength in geologic materials and is a direct function of the normal force.Cohesion results from a bonding between the surfaces of particles. It is caused by electro-chemical forces and is independent of normal forces.Influencing FactorsStrength is not a constant value for a given material, but rather is dependent upon manyfactors, including material properties, magnitude and direction of the applied force andthe rate of application, drainage conditions in the mass, and the magnitude of the confin-ing pressure.Stress Conditions In SituImportanceA major factor in strength problems is the existence of stress conditions in the ground, pri-marily because normal stresses on potential failure surfaces result from overburden pres-sures.Geostatic StressesOverburden pressures, consisting of both vertical and lateral stresses, exist on an elementin the ground as a result of the weight of the overlying materials. Stress conditions forMeasurement of Properties 163���NwNfPTT = N tan �Tmax = Nf = N tan �FIGURE 2.18Frictional force f resisting shearing force T [P � forceapplied in increments until slip occurs; N � normalforce component including block weight W; T �shearing stress component; f � frictional resistance; α� angle of obliquity [resultant of N and T]; φ �friction angle, or αmax at slip; Smax � maximumshearing resistance � Tmax].CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 163level ground are illustrated in Figure 2.19; sloping ground results in more complex condi-tions. (Changes in geostatic stresses are invoked by surface foundation loads, surface andsubsurface excavations, lowering of the groundwater level, and natural phenomena suchas erosion and deposition). Vertical earth pressures from overburden weight alone arefound by summing the weights from the various strata as follows:σv ��z0γn Zn (2.13)Coefficient of lateral earth pressure “at-rest” K0 is the ratio of the lateral to vertical stress in anatural deposit that has not been subject to lateral strain, the values for which vary sub-stantially with material types and properties (see Section 2.4.2). It is expressed asK0 � σh/σv (2.14)orσh � K0 σv (2.15)For an elastic solid K0 � ν/1�ν (2.16)In the above expressions, γ is the material unit weight (γn above groundwater level, γbbelow groundwater level) and ν is the Poisson’s ratio (see Section 2.5.1).Total and Effective StressesThe total stress on the soil element in Figure 2.19 at depth z is σv � γtZ (2.17)If the static water table is at the surface, however, and the soil to depth z is saturated, thereis pressure on the water in the pores because of a piezoelectric head hw and the unit weightof water γw. This is termed the neutral stress (acting equally in all directions), or the pore-water pressure uw or u and is given asu � σwhw (2.18)The effective stress σv, or actual intergranular stresses between soil particles, results froma reduction caused by the neutral stress and is equal to the total stress minus the pore-water pressure, orσv � σv � u (2.19)164 Geotechnical Investigation Methods∞�1�2�3 σvσhK0�zσhσvzz1z2z3FIGURE 2.19 The geostatic stress condition and “at-rest” earthpressures.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 164orσv � γbz (2.20)where γb � γt � γw is the effective or submerged soil weight.In calculations, therefore, above the groundwater level, the effective soil weight is thetotal weight γt, and below the groundwater level (or any other water surface), the effectivesoil weight is the submerged soil weight γb.Prestress in Soil FormationsGeneral: Soils compress naturally under the weight of overlying materials or some otherapplied load, resulting in strength increase over values inherent as deposited, or shortlythereafter. Three categories of prestress are defined according to the degree of compression(termed consolidation) that has occurred.Normally consolidated (NC): The soil element has never been subjected to pressuresgreater than the existing overburden pressures.Overconsolidated (OC): The soil element has at some time in its history been subjected topressures in excess of existing overburden, such as resulting from glacial ice loads,removal of material by erosion, desiccation, or lowering of the groundwater level.Underconsolidated (UC): The soil element exists at a degree of pressure less than existingoverburden pressures. This case can result from hydrostatic pressures reducing overbur-den load as illustrated in Figure 2.20. Such soils are normally relatively weak. Weakeningof strata can also occur due to removal of a cementing agent or other mineral constituentsby solution.Principal Stresses and the Mohr DiagramImportanceFundamental to the strength aspects of geologic materials are the concepts of principalstresses and the Mohr diagram on which their relationships may be illustrated.Measurement of Properties 165Hydrostatic head removes some effective overburdenpressure; load on soil can be less than existingoverburden load (under consolidated)SandCementing agent dissolvedleaving loose structureCementing agent in granular soilsSolution of cementing agentRainfallHydrostatic uplift(approximate)∆HClayFIGURE 2.20Soil profile weakening processes.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 165Principal StressesStresses acting on any plane passed through a point consist of a normal stress σ (com-pression or tension) and a shearing stress τ. (Soil mechanics problems are normally con-cerned with compressive stresses.) On one particular plane, the normal stress will be themaximum possible value and the shearing stress will be equal to zero. On one plane per-pendicular to this plane, the normal stress will be the minimum possible value, with shearstress also equal to zero. On a second plane perpendicular to this plane, the normal stresswill have an intermediate value and the shearing stress will also be zero. These planes aretermed the principal planes.The principal stresses are the stresses acting perpendicular to the principal planesincluding the maximum (major) principal stress σ1, the minimum (minor) principal stressσ3, and the intermediate principal stress σ2. The relationship between principal stressesand the normal stress and the shear stress acting on a random plane through a point isshown in Figure2.21. The intermediate principal stress is the plane of the paper and, insoil mechanics problems, is normally considered to be equal to σ3.The Mohr DiagramTo attain equilibrium, the sum of the forces given in Figure 2.21 should be zero. Therefore,σn and τ can be expressed in terms of the principal stresses and the angle θ as σn � [ (σ1 � σ2 )/2 � (σ1� σ3 )/2 ] cos 2θ (2.21)τ � [( σ1� σ3 )/2] sin 2θ (2.22)If points are plotted to represent coordinates of normal and shearing stresses acting on aparticular plane for all values of θ given in equations 2.21 and 2.22, their loci form a circlewhich intersects the abscissa at coordinates equal to the major (σ1) and minor (σ3) principalstresses. The circle is referred to as the Mohr diagram, or Mohr’s circle, given in Figure 2.22.Applications of Strength ValuesStability AnalysisThe values for strength are used in stability analyses; the discussion is beyond the scope ofthis book, except for evaluations of slopes. In general terms, stability is based on plastic equi-librium or a condition of maximum shear strength with failure by rupture imminent. Whenthe imposed stresses cause the shear strength to be exceeded, rupture occurs in the massalong one or more failure surfaces. Analyses are normally based on the limit equilibrium166 Geotechnical Investigation Methodsσnσ1σ3���sin �cos �τnOpABFIGURE 2.21Stresses on a random plane through a point (σ2 is the planeof the paper).CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 166approach, i.e., a limiting value that can be reached when the forces acting to cause failureare in balance with the forces acting to resist failure. Resistance to failure is provided bythe shear strength mobilized along the failure surface.Typical ProblemsSome field conditions involving failure by rupture are illustrated in Figure 2.23, showingthe relationships between the force acting to cause failure, the strength acting along thefailure surface, and the principal and normal stresses.2.4.2 Shear Strength RelationshipsBasic ConceptsShear strength may be given in several forms, depending on various factors, including thedrained strength, the undrained strength, the peak strength, the residual or ultimatestrength, and strength under dynamic loadings. In addition, strength is the major factor indetermining active and passive Earth pressures.Under an applied force, a specimen will strain until rupture occurs at some peak stress;in some materials, as strain continues, the resistance reduces until a constant minimumvalue is reached, termed the ultimate or residual strength.Factors Affecting StrengthMaterial type: Some materials exhibit only a frictional component of resistance φ; othersexhibit φ as well as cohesion c. In soft clays, at the end of construction, it is normally theundrained strength s that governs.Confining pressure: In materials with φ acting, the strength increases as the confiningpressure increases.Measurement of Properties 167A(σn,τ)σ1−σ3τmax = 2σnf2�cNormal stressσ3σ1σ1σ3+Shearing stress τ�cFIGURE. 2.22The Mohr diagram relating τ, σnf, σ3, and σ1 (θcr � θ at failure; σnf � normal stress at failure).CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 167Undrained or drained conditions: It relates to the ability of a material to drain underapplied stress and determines whether total or effective stresses act.Loading direction: Forces applied parallel to weakness planes, as represented by stratifi-cation in soils, foliation planes, or joints in rock masses, will result in lower strengths thanif the force is applied perpendicularly. Compressive strengths are much higher than ten-sile strengths.Displacement and normal stress: In some cohesive materials, such as overconsolidated fis-sured clays and clay shales, the strain at which the peak stress occurs depends on the nor-mal stress level and the magnitude of the peak strength varies with the magnitude ofnormal stress (Peck, 1969) as shown in Figure 2.24. As strain continues the ultimate strengthprevails. These concepts are particularly important in problems with slope stability.Angle of Internal Friction φThe stresses acting on a confined specimen of dry cohesionless soil, either in the ground orin a triaxial testing device (see Section 2.4.4), are illustrated in Figure 2.25. p is the appliedstress, σ3 is the confining pressure, and σ1 � p � σ3 (in testing p is termed the deviator stressσd). As stress p is gradually increased, it is resisted by the frictional forces acting between168 Geotechnical Investigation MethodsFFFFPPPPPSSSSS PPPPσnσnσnσn σnσ1σ3σ3σ3σ3σ1σ1σ1F(a)(c)(e)(b)(d)(f)FSFIGURE 2.23Some field conditions involving failure by rupture: (a) foundations; (b) retaining structures; (c) slopes; (d) ground anchors; (e) wall anchors; (f) embankments.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 168grains until some characteristic stress level is reached at which resistance is exceeded andrupture occurs. This stress is termed the peak strength.If σ3 and σ1 (for the peak strength) are plotted to define a Mohr’s circle at failure, a linedrawn tangentially to the circle passes through the origin at an angle φ as shown in Figure2.26 and Figure 2.27. Other specimens of the same material loaded to failure, but at differentconfining pressures, will have Mohr’s circles tangent to the line defined by φ. The circle tan-gent line represents the limits of stability and is termed Mohr’s envelope. It defines shearstrength in terms of the friction angle φ, and the normal or total stresses, and it expressed ass � τmax � σn tan φ (2.23)(In actuality, the envelope line will not be straight, but will curve downward slightly athigher confining pressures.)Total vs. Effective Stresses (φ vs. φ)In a fully saturated cohesionless soil, the φ value will vary with the drainage conditionsprevailing during failure. In undrained conditions, total stresses prevail and in drainedconditions, only effective stresses act. The friction angle is expressed as φ.Total StressesSaturated SoilsIf no drainage is permitted from a fully saturated soil as load is applied, the stress at fail-ure is carried partially by the pore water and partially by the soil particles which thusMeasurement of Properties 169σn = 5 kg/cm2σn = 3 kg/cm2σn = 1 kg/cm2σn = 0.5 kg/cm2Peak strengths∆L�FIGURE 2.24Peak strength vs. displacement and normal stress.(From Peck, R. B., Proceedings of ASCE, Stability andPerformance of Slopes Embankments, Berkeley, CA,1969, pp. 437–451. With permission.)Pσ3σ3 σ3σnσ1τ�σ1Tan � = τ/σnFIGURE 2.25Stresses on a specimen in a confined state.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 169develop some intergranular stresses. The peak “undrained” strength parameters mobi-lized depend on the soil type:● Cohesionless soils — the envelope passes through the origin (Figure 2.26 andFigure 2.27) and strength is expressed in terms of φ as in equation 2.23.● Soils with cohesion — the envelope intercepts the shear stress ordinate at a valuetaken as cohesion c, similar to the case shown in Figure 2.28, and the strength isexpressed by the Mohr–Coulomb failure law:s � c � σn tan φ (2.24)170 Geotechnical Investigation MethodsShearing strength s Effective stressP3P3P1P1udfudfTotalstress�dFIGURE 2.26Mohr’s envelopes for total and effectivestresses from CU triaxial tests on loosesaturated sands.Shearing strength sEffective stressP1P1P1P3udf udfTotal stress� dNormal stress P FIGURE 2.27Mohr’s envelopes for total and effective stressesfrom CU triaxial tests on dense saturated sands.Shear stress τcConfining, applied and normal stresses�τmax = c + σntan �σ FIGURE 2.28Drained triaxial test on soil with cohesion.CRC_42742_Ch002.qxd 9/22/20068:48 AM Page 170● Normally to slightly overconsolidated clays have no frictional component (φ �0) and the strength is expressed as the undrained strength su, as will be discussedlater.Applicable Field Conditions● Initial phases of slope excavations or retaining wall construction in slowly drain-ing soils, where time is too short to permit drainage. (Results are conservative ifdrainage occurs.)● Sudden drawdown conditions in the upstream slope of a dam embankment, orwhen flood waters recede rapidly from stream banks and the soils remain satu-rated.● Rapid placement of embankments or loading of storage tanks over soft clays, orhigh live loads applied to slow-draining soils.Effective StressesSaturated SoilsIf the soil is permitted to drain as load is applied, the stress is initially carried partly by thepore water, but as drainage occurs the load is transferred to the soil grains, and the effec-tive stresses (intergranular stresses) are mobilized. The effective stress is equal to the totalnormal stress σn minus the pore-water pressure u, and the peak “drained” shear strengthis expressed ass � (σn � u)tan φ � σn tan φ (2.25)As shown in Figures 2.26 and 2.27, φ values based on effective stresses are often higherthan those based on total stresses as long as u is positive. In dense sands, u is negative andthe undrained strength is higher, i.e., φ is higher. If pore pressures are measured duringundrained loadings, effective stresses can be computed.For soils with a cohesion intercept (Figure 2.28), the drained strength is expressed by theCoulomb–Terzaghi equation ass � c � (σn � u)tan φ � c� σn tan φ (2.26)Applicable Field ConditionsDrained strength prevails in the field under relatively slow loading conditions duringwhich pore pressures can dissipate. Such conditions generally exist in:● Most foundations, except for cases involving rapid load application.● Natural slopes, except for the sudden drawdown case.● Cut slopes, embankments, and retaining structures some time after constructioncompletion.Partially Saturated SoilsIn partially saturated soils, strength is controlled by effective stresses, but the effectivestress concept cannot be applied directly because of pressures in the air or gas in the par-tially saturated voids. Strength should be estimated from tests performed to duplicate insitu conditions as closely as possible in terms of percent saturation, total stress, and pres-sure on the liquid phase (Lambe and Whitman, 1969).Measurement of Properties 171CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 171Apparent cohesion results from capillary forces in partially saturated fine-grained granu-lar soils, such as fine sands and silts, and provides a temporary strength which is lost uponsaturation or drying. The apparent cohesion has been expressed in terms of the depth Dto the water table (Lambe and Whitman, 1969) asca � Dγw tan φ (2.27)Pore-Pressure ParametersDefinitionPore-pressure parameters express the portion of a stress increment carried by the porefluid in terms of the ratio of the pore-pressure increment (∆u) to the total stress increment(∆σ). As indicated in Lambe and Whitman (1969) and Bishop and Henkel (1962), theparameters areC � ∆u/∆σ1 (2.28)for loading in the odeometer (one-dimensional compression),B � ∆u/∆σ (2.29)for isotopic loading (three-dimensional compression),A � (∆u � ∆σ3)/(∆σ1 � ∆σ3) (2.30)for triaxial loading andA � ∆u/∆σ1 (2.31)for the normal undrained test where σ3 � 0.Pore-pressure parameter A is the most significant in practice. Values depend on soil type,state of stress, strain magnitude, and time. Typical values are given in Table 2.17 for con-ditions at failure but important projects always require measurement by testing.High values occur in soft or loose soils. Negative values indicate negative pore pres-sures, which occur in dense sands and heavily preconsolidated clays as the result of vol-ume increase during shear (dilatancy). Pore pressures are most responsive to applied172 Geotechnical Investigation MethodsTABLE 2.17Typical Values of Pore-Pressure Parameter A at FailureaSoil Type Parameter ASensitive clay 1.5–2.5Normally consolidated clay 0.7–1.3Overconsolidated clay 0.3–0.7Heavily overconsolidated clay �0.5–0.0Very loose fine sand 2.0–3.0Medium fine sand 0.0Dense fine sand �0.3Loess �0.2a From Lambe, T.W., Proc. ASCE, J. Soil Mech. Found. Eng. Div., 88, 19–47, 1962.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 172stress in sensitive clays and loose fine sands that are subject to liquefaction. In soft or loosesoils, higher shear strain magnitudes result in higher values for parameter A.ApplicationsPore-pressure parameter A is used to estimate the magnitude of initial excess pore pres-sure produced at a given point in the subsoil by a change in the total stress system. Withpiezometers used to measure in situ pore pressures, the validity of the estimates can beverified and the loading rate during surcharging or embankment construction can be con-trolled to avoid failure caused by exceeding the undrained shear strength.Undrained Shear Strength suConceptsDuring undrained loading in soft to firm saturated clays, the applied stress is carriedpartly by the soil skeleton and partly by the pore water. Increasing the confining pressuredoes not increase the diameter of Mohr’s circle, since the pore pressure increases as muchas the confining pressure. The undrained strength, therefore, is independent of an increasein normal stress (φ � 0), and as shown in Figure 2.29, is given by the expressionsu � ½ σd (2.32)where σd � (σ1�σ3) is the applied or deviator stress. In the figure, Uc represents the uncon-fined compressive strength where σ3 � 0. As shown, su � 1/2Uc.For NC clays, su falls within a limited fraction of the effective overburden pressure (σv or p), usually in the range su/p � 0.16 to 0.4 (based on field vane and K0triaxial tests). Therefore, if su � 0.5p the clay may be considered as overconsolidated (seeSection 2.5.2).Factors Affecting su ValuesTime rate of loading: For soft clays, su, measured by vane shear tests, has been found to begreater than the field strength mobilized under an embankment loading, and the differ-ence increases with the plasticity of the clay (Casagrande, 1959; Bjerrum, 1969, 1972). Thedifference is attributed to the variation in loading time rates; laboratory tests are per-formed at much higher strain rates than those that occur during the placement of anembankment in the field, which may take several months. A correction factor, therefore, isoften applied to test values for su (see Section 2.4.4).Measurement of Properties 173τσ3 σ1σUcSu = CFIGURE 2.29Undrained tests on saturated soil with cohesion.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 173Direction of loading: Soil anisotropy may cause shear strength measured in a horizontaldirection to be significantly higher than when measured in a vertical direction (see In SituVane Shear Test, in Section 2.4.4).Residual or Ultimate Shear Strength sr, or φφrConceptsThe lowest strength that a cohesive material can attain in the confined state is termed theultimate strength. In many cohesive materials, if strain continues past the peak strengthunder continued stress, the strength will decrease until some minimum value is reached.Thereafter, strength remains constant with increasing strain as shown in Figure 2.30.Residual strength is a strength lower than peak strength remaining after failure hasoccurred. It has become generally accepted that the residual strength is the lowest strengththat can be obtained during shear. In a normally consolidated clay the remolded undrainedshear strength is considered to be equal to the ultimate or residual strength sr.The envelope for the ultimate drained strength passes through the origin as a straight lineon the Mohr diagram and has no cohesion intercept(even in cohesive materials) as shown inFigure 2.31 (Lambe and Whitman, 1969). The drained ultimate shear strength is expressed as s � σn tan φr (2.33)Other FactorsNatural slopes: The residual strength, rather than the peak strength, often applies. Anapproximate relationship between φr and plasticity index for rock gouge materials is givenin Figure 2.32.174 Geotechnical Investigation MethodsPeak strength−overconsolidated clayPeak strength−normally consolidated clayUltimate strength�DisplacementFIGURE 2.30Peak and ultimate strength vs. displacement.σ�r� rτmax = σntanτFIGURE 2.31Mohr’s envelope for ultimate drainedstrength in clay.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 174Sensitivity St: The ratio of the natural peak strength to the ultimate undrained strengthwhen a sample is completely remolded at unaltered water content is referred to as the soilsensitivity, expressed asSt � su/sr (2.34)A clay classification based on St is given in Table 2.18. Soils termed as “quick” have highsensitivities and are extremely sensitive to vibrations and other forms of disturbance. Theycan quickly lose their strength, change to a fluid, and flow, even on very flat slopes.Thixotropy refers to the regain in strength occurring in remolded soils because of a “reha-bilitation of the molecular structure of the adsorbed layers” (Lambe and Whitman, 1969).Dynamic ShearConceptsUnder dynamic or cyclic loading a soil specimen subject to shear initially undergoes defor-mations that are partially irreversible, irrespective of the strain amplitude; hence,stress–strain curves in loading and unloading do not coincide. If strain amplitude is small,the difference between successive reloading curves tends to disappear after a few loadingMeasurement of Properties 1752020 60 804030100Plasticity index (%)Drained angle of shearing resisitance �r (deg) FIGURE 2.32Approximate relationship between thedrained angle of residual shearingresistance and plasticity index for rockgouge material. (From Patton, F. D. andHendron Jr., A. J., Proceedings of the 2ndInternational Congress, InternationalAssociation Engineering Geology, SaoPaulo, 1974, p. V-GR. 1. Kanji, M. A., M.S. Thesis, Department of Geology,University of Illinois, Urbana, 1970. Withpermission.)TABLE 2.18Clay Classification by Sensitivity StaSensitivity su/srb Classification2 Insensitive2–4 Moderately sensitive4–8 Sensitive8–16 Very sensitive16–32 Slightly quick32–64 Medium quick64 Quicka From Skempton, A.W., Proceedings of the 3rd International Conference on Soil Mechanics and FoundationEngineering, Switzerland, Vol. I, 1953, pp. 57–61.b su � peak undrained strength, st � remolded strength.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 175cycles of a similar amplitude and the stress–strain curve becomes a closed loop that can bedefined by two parameters as shown in Figure 2.33:● Shear modulus (Section 2.5.2) is defined by the average slope and has been foundto decrease markedly with increasing strain amplitude.● Internal damping refers to energy dissipation and is defined by the enclosed areasas shown in the figure (damping ratio λ).In clay soils, if strain amplitude is large there is a significant reduction in the undrainedstrength.In cohesionless soils, pore pressure increases almost linearly with the number of cyclesuntil failure occurs. The simple shear device used for dynamic testing in the laboratory isshown on Figure 2.34. Liquefaction occurs when pore pressures totally relieve effectivestresses.Field OccurrenceWave forces against offshore structures cause low-frequency cyclic loads. Seismic wavesfrom earthquakes cause low- to high-frequency cyclic loads.At-Rest, Passive, and Active Stress StatesAt-Rest Conditions (K0)The coefficient of lateral at-rest earth pressure has been defined as the ratio of lateral tovertical stress, K0 � σh/σv (Equation 2.15).For sands and NC clays, K0 is normally in the range of 0.4 to 0.5 and is a function of φ inaccordance withK0 � 1.0 � sin φ (2.35)176 Geotechnical Investigation Methods4πATDefinitions: For G2Shear modulus, G =G2G11 11G2Damping ratio, D =AL = Loop areaAT = Triangle areaLocus of hysteresisloops tipsShear stress τ(1) =AL(1)Shear strain ζζ2 FIGURE 2.33Hysteretic stress-strain relationship fromcyclic shear test at different strainamplitudes. (After USAEC, NationalTechnical Information ServicePublication TID-25953, U. S. Departmentof Commerce, Oak Ridge NationalLaboratory, Oak Ridge, TN, 1972.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 176In clay soils, K0 has been found to be directly related to the amount of prestress or pre-consolidation in the formation, ranging from 0.5 to almost 3. The degree of prestress isgiven in terms of the overconsolidation ratio (OCR), i.e., the ratio of the maximum pastpressure to the existing overburden pressure (see Section 2.5.4).Passive State of Stress (Kp)The passive state exists when a force pushes against a soil mass and the mass exerts itsmaximum resistance to the force. The principal stresses for the passive state are shown inFigure 2.35a; as the soil element is pushed, the vertical stress remains unchanged but thehorizontal stress increases (σh � σv). As movement continues the shear stress increasesfrom the at-rest condition (1) until σh � σv (2), then continues to increase as slip lines (rup-ture planes) form and finally failure occurs at (4). At this point of plastic equilibrium, thepassive state has been reached.The relationship between φ and the principal stresses at failure, as shown on the Mohrdiagram of Figure 2.35a, may be expressed for a cohesionless granular soil with a hori-zontal ground surface asσ1/σ3 � σv/σh � (1 � sin φ)/(1 � sin φ) (2.36)Measurement of Properties 177VerticalconsolidationloadFixedplateTopplateHorizontaldisplacementtransducerSpecimenWine-ReinforcedrubbermembraneRubbercuringLoadcellCyclic forceFcapplied viaload cellon top capClampFixedbottomplatePedestalBottom capClampde = horizontal cyclic displacement amplitudeFe = horizontal cyclic shear forceH = height of specimenA = area of specimen�o = do / H = horizontal cyclic shear strain amplitudeτo = Fo / A = horizontal cyclic shear stress amplitudeHFIGURE 2.34NGI-type simple shear device at the UCLA Soil Dynamics Laboratory. (From Vucetic, 2004.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 177orσv/σh � tan2 (45° � φ/2) � Kp (2.37)where Kp is the coefficient of passive stress.Active State of StressThe active state exists when a soil mass is allowed to stretch, for example, when a retain-ing wall tilts and σv �σh. In Figure 2.35b, as the mass stretches, σv remains unchanged andσh decreases (2) until the induced shear stress is sufficient to cause failure (3). At this pointof plastic equilibrium, the active state has been reached.The coefficient of active stress Ka, (the ratio σh/σv) represents a minimum force,expressed for a cohesionless soil with a horizontal ground surface asKa � tan2 (45° � φ/2) (2.38)andKa � 1/Kp (2.39)ApplicationsThe at-rest coefficient K0 has a number of practical applications. It is used to compute lateralthrusts against earth-retaining structures, where lateral movement is anticipated to be toosmall to mobilize Ka. It is fundamental to the reconsolidation of triaxial test specimensaccording to an anisotropic stress path resembling that which occurred in situ (CKoU tests).It is basic to the computation of settlements in certain situations (Lambe, 1964). It has beenused for the analysis of progressive failure in clay slopes (Lo and Lee, 1973), the predictionof pore-water pressure in earth dams (Pells, 1973), and the computation of lateral swellingpressures against friction piles in expansive soils (Kassif and Baker, 1969).178 GeotechnicalInvestigation Methodsτ τσhσfσh1σh2 σh3 σh3σh4 σ3σh2σv = σh = σh1 σ1= σv= Kp σvσvσhσfτf= Kaσvσv P(1) At rest(2) Aftermovement(3) After moremovement(2) After slightmovement(1) At restSlip lines45 + �/2 to planeon whichσ1 = σh acts45 + �/2 to planeon whichσ1 = σh actsSlip linesQQCompression Extension(a) (b)(4) Passive stateof failure(3) Active stateof failurePτfFIGURE 2.35Mohr diagrams for the (a) passive and (b) active states of stress.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 178Coefficients of lateral earth pressure is the term often used to refer to Kp and Ka. When rup-ture occurs along some failure surface, earth pressures are mobilized. The magnitudes ofthe pressures are a function of the weight of the mass in the failure zone and the strengthacting along the failure surface. These pressures (Pp or Pa) are often expressed in terms ofthe product of the weight of the mass times the active or passive coefficients, as follows:Pp � Kpγ z (2.40)Pa � Kaγ z (2.41)Examples of the occurrence of Pp and Pa in practice are given in Figure 2.36.2.4.3 Rock Strength MeasurementsGeneralIntact RockThe confined strength of fresh, intact rock is seldom of concern in practice because of therelatively low stress levels imposed.Brittle shear failure occurs under very high applied loads and moderate to high confin-ing pressures, except for the softer rocks such as halite, foliated and schistose rocks, andlightly cemented sandstones. In softer rocks, rupture occurs in a manner similar to that insoils, and the parameters described in Section 2.4.2 hold.Under very high confining pressures (approximately 45,000 psi or 3000 bar), some com-petent rocks behave ductilely and failure may be attributed to plastic shear (Murphy,Measurement of Properties 179CompressionPassive zone++−TensionCracks PassivewedgeActive wedgeWFailuresurfaceActivezonePrandtl zonePassive zoneRQFPaPpW2W1PpPaRPpFpActive zoneFailuresurface(a)(c) (d) (e)(b)FIGURE 2.36Examples of the occurrence of active and passive pressures encountered in practice: (a) slope; (b) retainingwall; (c) anchored bulkhead; (d) anchor block; (e) foundation.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 1791970). Intact specimens are tested in uniaxial compression or tension to provide data forclassification and correlations. Other tests include those for flexural strength and triaxialcompressive strength. Applied forces for the various tests are shown in Figure 2.37.Rock MassesRock-mass strength is normally controlled either by the joints and other discontinuities orby the degree of decomposition, and the strength parameters described in Section 2.4.2here. Strength is measured in situ by direct shear equipment or special triaxial shear equip-ment.Uniaxial Compressive Strength Uc (ASTM D2938)ProcedureAn axial compressive force is applied to an unconfined specimen (Figure 2.38) until fail-ure occurs.Data ObtainedA stress–strain curve and the unconfined or uniaxial compressive strength (in tsf, kg/cm2,kPa) result from the test. Stress–strain curves for various rock types are given in Table 2.24.Data ApplicationsPrimarily used for correlations as follows:● Material “consistency” vs. Uc — Figure 2.39.● Schmidt hardness vs. Uc — Figure 2.40. The Schmidt hardness instrument(Figure 3.1a) is useful for field measurements of outcrops to correlate variationsin Uc. Corrections are available for inclinations from the vertical.● Hardness classification.180 Geotechnical Investigation Methodsσdσdσd σdσdσdσdσdσ3σ3σNσNσ3(f)(e) (g) (h)(d)(c)(b)(a)FIGURE 2.37Common laboratory tests to measure strength of rock cores: (a) uniaxial compression; (b) triaxial compression;(c) direct shear for soft specimens; (d) direct shear for joints; (e) point load; (f) direct tension; (g) splittingtension (Brazilian); and (h) four-point flexural.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 180Measurement of Properties 181Shear cracksPPFIGURE 2.38Uniaxial compression test.Unconfined compressive strength (tsf)Unconfined compressive strength (psi)Very soft soil6.8 680680.68 6800Minimum strengthenvelopeConsistencyRock defined at 100 psi1.0 10010 1000 100,00010,000Soft soilFirm soilStiff soilHard soilVery soft rockSoft rockHard rockVery hard rockExtremely hardrockFIGURE 2.39Relationship between “consistency” and Uc (100 psi � 6.8 kg/cm2 � 689.5 kN/m2). (After Jennings, J. E.,Proceedings of ASCE, 13th Symposium on Rock Mechanics, University of Illinois, Urbana, 1972, pp. 269–302.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 181Uniaxial Tensile StrengthCable-Pull TestCaps are attached to the ends of a cylindrical specimen with resins. The specimen is thenpulled apart by cables exerting tension axially (Figure 2.37f). The method yields the low-est values for tensile strength, which generally ranges from 5 to 10% of the uniaxial com-pression strength.Point-Load Test (Broch and Franklin, 1972) (ASTM D5731-95)Compressive loads P are applied through hardened conical points to diametrically oppo-site sides of a core specimen of length of at least 1.4D until failure occurs. The equipmentis light and portable (Figure 2.41) and is used in the field and the laboratory.Point-load index is the strength factor obtained from the test, and is given by the empiri-cal expression (Hoek and Bray, 1977)Is � P/D2 (2.42)where D is the diameter.182 Geotechnical Investigation MethodsComprehensive strength Uc of rock surface (MPa)350300250200150100908070605040302015100 10 20 30Schmidt hardness R,L hammer±20±40±60±80±100±200Hammer vertical downwards40 50 6030Rock density = 32 31Average dispersion ofstrength for most rocks29282726252423222120kNFIGURE 2.40Correlation chart for Schmidt L. hammer, relating rock density, uniaxial compressive strength, and reboundnumber R (Schmidt hardness). Hammer vertical downward; dispersion limits defined for 75% confidence.(Note: 100 MPa � 14.5 � 103 psi � 1021 tsf; 1 kN/m2 � 6.3 pcf.) (From ISRM, Rock Characterization and Monitoring, E. T. Brown, Ed., Pergomon Press, Oxford, 1981. With permission. After Deere, D. U. andMiller, R. P., Technical Report AFWL-TR-65-116, AF Special Weapons Center, Kirtland Air Force Base, NewMexico, 1966.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 182Values for Is are used to estimate Uc through various correlations as shown in Figure2.42, and, for a core diameter of 50 mm,Uc � 24 Is (2.43)Flexural Strength or Modulus of RuptureProcedureA rock beam is supported at both ends and loaded at midpoint until failure (Figure 2.37h).Data ObtainedThe flexural strength is proportional to the tensile strength but is about three times as great(Leet, 1960).Measurement of Properties 183FIGURE 2.41Point load strength test apparatus.Point-load strength index I s ( MPa)Point-load strength index I s (psi)205000 10 20Uniaxial compressive strength Uc, psi x 10330 40 50200kg/cm215010050Is1000 1500 2000 2500 3000 kg/cm2UcUc 50 100 150 200 250 300 MPa1510520001000500StrongNoriteWeakNoriteQuartziteSandstoneUc = 24 Is (for NX core)Experimentalpoint rangePoint-load strengthindex = Is = P/D2CoreL = 0.7 D(min)LPDFIGURE 2.42Relationship between point load strength index Is and uniaxial compressive strength Uc. (After Bieniawski, Z.T., Proceedings 3rd International Congress for Rock Mechanics, International Society for Rock Mechanics, Vol. IIA,Denver, 1974, pp. 27–32. Reprinted with permission of National Academy Press.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 183Triaxial Shear StrengthApparatus and ProceduresGeneraldescription is given in Section 2.4.4 and, as applicable to rock testing, in Section2.5.3 and in Table 2.28.Strength ValuesStudies have been made relating analysis of petrographic thin sections of sandstone to esti-mates of the triaxial compressive strength (Fahy and Guccione, 1979). Relationships havebeen developed for approximating peak strengths for rock masses (Hoek and Brown, 1980).Direct Shear Strength PurposeThe purpose is to obtain measurements of the parameters φ and c in situ. It is particularlyuseful to measure strength along joints or other weakness planes in rock masses.In Situ Test ProcedureA diamond saw is used to trim a rock block from the mass with dimensions 0.7 to 1.0 m2and 0.3 m in height, and a steel box is placed over the block and filled with grout(Haverland and Slebir, 1972). Vertical load is imposed by a hydraulic jack, while a shearforce is imposed by another jack (Figure 2.43) until failure. All jack forces and block move-ments are measured and recorded. Deere (1976) suggests at least five tests for each geo-logic feature to be tested, each test being run at a different level of normal stress to allowthe construction of Mohr’s envelope.Laboratory Direct Shear Tests (See Section 2.4.4)If the specimen is decomposed to the extent that it may be trimmed into the direct shearring (Figures 2.37c and 2.51) the test is performed similar to a soil test (Section 2.4.4). If pos-sible, the shearing plane should coincide with the weakness planes of the specimen. Teststo measure the characteristics of joints in fresh to moderately weathered rock are performedby encapsulating the specimen in some strong material within the shear box as shown inFigure 2.37d (ISRM, 1981). The specimen is permitted to consolidate under a normal forceand then sheared to obtain measures of peak and residual strength as described in Section2.4.4. The normal stress is increased, consolidation permitted, and the specimen shearedagain. The process is repeated until five values of shear stress vs. normal stress is obtained,from which a graph for peak and residual strength is constructed as shown in Figure 2.44.184 Geotechnical Investigation MethodsReactionThrustjackLoad jackSteel padSteel frameRockblock1 − 0.7 m FIGURE 2.43In situ direct shear test.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 184Shear strength parameters φa, φb, φr, c and c are abstracted from the graph, which oftenis a composite of several tests, as shown in Figure 2.44 where● φr � residual friction angle. ● φa � apparent friction angle below stress σa; point A is a break in the peak shearstrength curve resulting from the shearing off of the major irregularities (asperi-ties) on the shear surface. Between points O and A, φa will vary slightly and ismeasured at the stress level of interest (φa � φu � j where φu is the friction angleobtained for smooth surface of rock and angle j is the inclination of surfaceasperities) (Figure 2.45).● φb � the apparent friction angle above stress level σa ; it is usually equal to orslightly greater than φr, and varies slightly with the stress level. It is measured atthe level of interest.● c � cohesion intercept of peak shear strength which may be zero.● c � apparent cohesion at a stress level corresponding to φb.Borehole Shear Test (BST) (ASTM D4917-02)PurposeThe borehole shear test measures peak and residual values of φ and c in situ. Initiallydeveloped at Iowa State University by R.L. Handy and N.S. Fox for the U.S. Bureau ofMeasurement of Properties 185Shear stress τ Peak shear strengthResidual shear strengthNormal stress σnσa�a�bACC ′FIGURE 2.44Shear strength–normalized stressgraph for direct shear test onrock specimen.Shear displacement δsδn = δs tan jτ = σN tan (� +j)(3.59)σσσσ(a) (b)j angles forsecond-orderprojectionsNormal displacement δnAverage j anglesfor first-orderprojectionsFIGURE 2.45The joint roughness angle j: (a) experiments on shearing regular projection and (b) measurements of j anglesfor first- and second-order projections on rough rock surface. (From Patton, F. D., Proceedings of the 1stInternational Congress of Rock Mechanics, Lisbon, Vol. 1, 1966, pp. 509–513. With permission.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 185186 Geotechnical Investigation MethodsMines, it was designed for near-surface or in-mine testing of coal and other fractured rocksthat are difficult to core. It has been used in all soft to medium-hard rocks.ProcedureThe apparatus is shown in Figure 2.46. A shear head, consisting of opposing plates withtwo carbide teeth, is lowered into a 3 in. (75 mm) borehole. Normal stress is applied by pushing the shear plates into the sides of the hole using a hand-operated pump. The pressure is then valved off so it remains constant, while the same pump is used topull the expanded shear head a short distance upward along the hole by means of a hol-low-ram jack. Both the expansion pressure and the pulling resistance are recorded, andthe test is repeated with different preselected normal stresses. Up to four tests can be con-ducted at the same depth by rotating the shear head 45° between tests. A plot of each testis made to obtain a Mohr’s envelope of shear stress vs. normal stress providing meas-urements of the angle of internal friction (φ) and cohesion (c) (Handy et al., 1976).Comparison with data from in situ direct shear tests indicate that cohesion values fromthe BST are lower although the friction angles are close (R. L. Handy, personal commu-nication, 2004).ApplicationsThe apparatus is used in both rock (RBST) and soil (BST) in vertical, inclined, or horizon-tal boreholes. The entire apparatus, including the shear head and pulling device, is easilyportable. A very significant advantage over other methods to measure shear strength isthat many tests can be run in a short interval of time, as many as ten per day, and yieldresults on-site that can indicate if more tests are needed.Threaded rodHollow jackDial gageTripodJack base plateHose connectorNX holeBST bodyHalf nut clampShear hoseShear platesRetract hoseNormal hoseRod couplingRW drill rodRW adapterFIGURE 2.46Schematic of borehole shear strength tester (BST) inthe borehole. (From USBM, Bureau of Mines, U.S.Department of Interior, New Technology No. 122,1981. With permission.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 1862.4.4 Soil Strength MeasurementsGeneralSelection of Test MethodA number of factors required for the selection of the method for testing soils, including thefollowing:● Loading conditions: static or dynamic.● Loading duration in the field: long-term (drained conditions) or short-term(undrained conditions).● Parameter desired: peak or ultimate (residual) strength.● Material suitability for undisturbed sampling and the necessity or desirabilityfor in situ testing.● Orientation of the field failure surface with that in the test; some cases areshown in Figure 2.47 and Figure 2.48. Stability analysis is often improperlybased on compression tests only, whereas direct shear and extension tests areoften required. Their strength values may differ significantly from the com-pressive parameters.Testing Methods Summarized● Soil laboratory static strength tests — Table 2.19.● In situ static strength tests — Table 2.20.● Laboratory dynamic strength tests — Table 2.33.Measurement of Properties 187Passive(a)(b)(c)(d)ActiveSK0 �s ZPTW1W2dl1l2 σ3σ3σ3σ3σNσNσNσNσ3σ1σ1σ1σ1σ1σ1aεbdTriaxial compressionpassiveTriaxial compressionTriaxial tensiontype Direct shearPassivepoint-dActivepoint - aCdSSSLSActiveFactor of safety = = Σ resisting forces and masses W2I2 + R Σ S − LW1I1Σ active driving forces and massesPassiveCRbaaTriaxial tension typeactiveActive pressure = PA= KA�s Zσ1σ3SFIGURE 2.47Probable natural stress and strain restraint conditions: (a) Retaining wall influence of lateral yielding onstresses. (b) Mass slide of excavated slope. Influence of lateral yielding. (c) Stress–strain relationscorresponding to lateral yield conditions in (b). (d) Angle of friction relations corresponding to lateral yieldconditions in (b). (From Burmister, D. M., ASTM Special Technical Publication No. 131, 1953. Reprinted withpermission of the American Society for Testing and Materials.)CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 187188 Geotechnical Investigation MethodsSkirtdepth SeafloorTest:(cyclic)DirectshearActivetriaxialDirectshearPassivetriaxialFIGURE 2.48Relevance of laboratory tests to shear strengthalong potential slip surface beneath offshoregravity structure. (From Kierstad and Lunne,International Conference on Behavior of OffshoreStructure, London, 1979. With permission.)TABLE 2.19Summary of Soil Laboratory Static Strength TestsTest (F � also field test) Parameter Reference CommentsMeasuredTriaxial compressionCD φ_, c_Figure 2.28 Most reliable method for effective stressesCU φ, c, φ�, c� Figure 2.49 Strength values higher than reality because su Figure 2.50 disturbance causes lower w% upon reconsol-Table 2.21 dation (see footnote c in Table 2.21)UU su Figure 2.29 Most representative laboratory value forundrained shear strength in compressionTriaxial extension φ�, c�, su Table 2.21 Normally consolidated clays yield values approximately one-third those of compression tests because of soil anisotropy (Bjerrum et al., 1972)Plain strain compression φ Table 2.21 Values are a few degrees higher than thoseor extension of normal triaxial test except for loose sands;more closely approach reality for retainingstructure (Lambe and Whitman, 1969)Direct shear box φ�, c�, φ�r Figure 2.51 Values most applicable where test failure surface has same orientation with field failure surface. Values generally lower than triaxial compression values for a given soil, but higher than triaxial extension. Most suitable test for determination of residual strengthφ� ,r from UD samplesSimple shear su, φ�, c� Figure 2.34 Horizontal plane becomes plane of maximum shear strain at failureUnconfined compression Su � 1/2 Uc Table 2.22 Strength values generally lower than realityVane shear (F) su, sr Table 2.22 Applies shear stress on vertical planesTorvane (F) su, sr Table 2.22 Shear occurs in a plane perpendicular to the axis of rotationPocket penetrometer (F) Su � 1/2 Uc Table 2.22 Yields approximate values in clays. Used primarily for soil classification by consistencyCalifornia bearing ratio (F) CBR value Figure 2.64 Used for pavement design. Empirical strength correlates roughly with UcCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 188Triaxial Shear TestPurposeTotal or effective stress parameters, either in compression or extension, are measured in the tri-axial shear apparatus. The test method is generally unsuited for measuring ultimate strengthbecause displacement is limited and testing parallel to critical surfaces is not convenient.Apparatus includes a compression chamber to contain the specimen (Figure 2.49) and asystem to apply load under controlled stress or strain rates, and to measure load, deflec-tion, and pore pressures (Figure 2.50).Specimens are usually 2.78 in. in diameter as extruded from a Shelly tube, or 1.4 in. indiameter as trimmed from an undisturbed sample. Specimen height should be between 2and 2.6 times the diameter.General ProceduresRate of loading or strain is set to approximate field-loading conditions and the test is runto failure (Bishop and Henkel, 1962).Confining pressures: Tests are usually made on three different specimens with the sameindex properties to permit defining a Mohr diagram. Test method variations are numer-ous. Specimens can be preconsolidated or tested at their stress conditions as extruded.Tests can be performed as drained or undrained, or in compression or extension. The var-ious methods, parameters measured, and procedures are summarized in Table 2.21. CUtests are covered in ASTM D4767-02.Direct Shear Test (ASTM D5607-02 for rock, ASTM D3080-03 for soils)PurposeThe purpose normally is to measure the drained strength parameters φ, c, and φr.Measurement of Properties 189Measurement of Properties 189TABLE 2.20Summary of Soil In Situ Static Strength TestsTest Parameters Reference CommentsMeasuredVane shear su, sr (direct test) Figure 2.56 Measures undrained strength by shearing two circular horizontal surfaces and a cylindrical verti-cal surface: therefore, affected by soil anisotropySPT φ�, su (indirect test) Section 2.4.5 Dr is estimated from N and correlated with soil gradation to obtain estimates of φ(Figure 2.93, Table 2.36)Consistency is determined from N and correlated with plasticity to obtain estimates of Uc (Figure 2.94, Table 2.37)CPT φ�, su (indirect test) Section 2.4.5 Various theoretical and empirical relationships have been developed relating qc to φ�, (Figure 2.61) su is expressed as in Equation (2.50) where Nkt is the cone-bearingcapacity factor (deep foundation depth correction factor) Pore-water pressure u is measured by some cones (piezocones)Pressuremeters su (indirect test) Section 2.5.4 Affected by material anisotropy, su is expressed as in Equation (2.77)California bearing CBR value Section 2.4.5 Field values generally less than lab values ratio because of rigid confinement in the lab moldCRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 189190 Geotechnical Investigation MethodsInlet pressurevalve Deviator stress σdσ3σ3Ram to apply loadRubbermembraneSoilsamplePorousstoneAManometerOutletvalveBSample drainage and waterpore-pressure connectionFluid pressureTransparentmaterialcontainerTTFIGURE 2.49Triaxial compression chamberarrangement.FIGURE 2.50The triaxial compression chamber, load application, and measurement system.CRC_42742_Ch002.qxd 9/22/2006 8:48 AM Page 190ApparatusThe test apparatus is illustrated in Figure 2.51.ProcedureThe specimen is trimmed to fit into the shear box between two plates, which can be per-vious or impervious, depending upon the drainage conditions desired, and a normal loadapplied which remains constant throughout the test. The test is normally run as a consol-idated drained (CD) test (sample permitted to consolidate under the normal load), but itMeasurement of Properties 191TABLE 2.21Triaxial Test MethodsaTest To Measure ProcedureConsolidated-drained (CD) or (S) Effective stress parameters φ_, c_Specimen permitted to drain and compression test consolidate under confining pressure until u � 0.Deviator stress applied slowlyto failure while specimen drains during deformationbConsolidated-undrained (CU) or Total stress parameters φ , c Specimen permitted to drain and(R) compression test (Figure 2.28) consolidate under confining pressure until u � 0.Deviator stress applied slowlyto failure, but specimen drainage not permittedEffective stress parameters φ_, c_Pore pressures are measured during test (see Pore-Pressure Parameters)CK0 U test su See Notes c and d belowUnconsolidated-undrained (UU) Undrained strength su Confining pressure applied but or (Q) compression test (Figure 2.29) no drainage or consolidationpermitted to reduce test time. Deviator stress applied slowlyto failure with no drainage permittedExtension tests as CD, CU, UU Lateral shear strength Maintain confining pressure constant and reduce axial stress, or maintain axial stress constant and increase confining pressure until failurePlane strain compression or Parameter φ in cohesionless Modified triaxial apparatus inextension test granular soils which specimen can strain onlyin axial direction and one lateraldirection while its dimension remains
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