National Academies Press: OpenBook

Manual on Subsurface Investigations (2019)

Chapter: Front Matter

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NCHRP Web-Only Document 258: Manual on Subsurface Investigations Glenn J. Rix Njoroge Wainaina Ali Ebrahimi Robert C. Bachus Maria Limas Rodolfo Sancio Brooke Fait Geosyntec Consultants, Inc. Raleigh, North Carolina Paul W. Mayne Georgia Institute of Technology Atlanta, Georgia Final Report for NCHRP Project 21-10 Submitted November 2018 ACKNOWLEDGMENT This work was sponsored by the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the Federal Highway Administration, and was conducted in the National Cooperative Highway Research Program (NCHRP), which is administered by the Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, or TDC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research. They are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; or the program sponsors. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. C. D. Mote, Jr., is president. The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.national-academies.org. The Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to increase the benefits that transportation contributes to society by providing leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Board’s varied committees, task forces, and panels annually engage about 7,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

C O O P E R A T I V E R E S E A R C H P R O G R A M S CRP STAFF FOR NCHRP Web-Only Document 258 Christoper J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Senior Program Officer Sheila A. Moore, Program Associate Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications Jennifer Correro, Assistant Editor NCHRP PROJECT 21-10 PANEL AREA TWENTY-ONE: SOILS AND GEOLOGY--TESTING AND INSTRUMENTATION Leo L. Fontaine, Connecticut DOT, Newington, CT (Chair) James A. Williams, III, Mississippi DOT, Jackson, MS James H. "Jim" Anspach, Cardno, Bend, OR Derrick D. Dasenbrock, Minnesota DOT, Maplewood, MN William P. Owen, California DOT, Sacramento, CA Xiong "Bill" Yu, Case Western Reserve University, Cleveland, OH Benjamin S. Rivers, FHWA Liaison

iv Table of Contents LIST OF TABLES ........................................................................................................................ x LIST OF FIGURES .................................................................................................................... xii AUTHOR ACKNOWLEDGMENTS....................................................................................... xvi ABSTRACT ............................................................................................................................... xvii SUMMARY .............................................................................................................................. xviii INTRODUCTION................................................................................................................... 1 Purpose ........................................................................................................................................ 1 Organization of the Manual ......................................................................................................... 1 1.2.1 Planning the Investigation ....................................................................................................... 1 1.2.2 Executing the Investigation ..................................................................................................... 2 1.2.3 Interpreting the Results of the Investigation ........................................................................... 3 1.2.4 Reporting and Presenting the Results of the Investigation ...................................................... 3 1.2.5 Supplemental Investigative Information ................................................................................. 3 1.2.6 Supplemental Administrative Information .............................................................................. 4 Key Complementary Resources .................................................................................................. 5 Chapter 1 References ............................................................................................................................... 6 GEOTECHNICAL UNCERTAINTY AND RISK .............................................................. 7 Introduction ................................................................................................................................. 7 Uncertainty .................................................................................................................................. 7 Geotechnical Risks ...................................................................................................................... 7 2.3.1 Technical Risk ......................................................................................................................... 8 2.3.2 Financial Risk .......................................................................................................................... 8 2.3.3 Risk Mitigation ........................................................................................................................ 9 2.3.4 Geotechnical Risk for Design-Build Projects ......................................................................... 9 Load and Resistance Factor Design and Subsurface Investigation ........................................... 10 Chapter 2 References ............................................................................................................................. 11 SUBSURFACE INVESTIGATION PROCESSES ............................................................ 12 Introduction ............................................................................................................................... 12 Types of Data Required for Subsurface Investigations ............................................................. 12 3.2.1 Subsurface Investigation Objectives ..................................................................................... 13 3.2.2 Review of Available Records ................................................................................................ 17 3.2.3 Site Reconnaissance .............................................................................................................. 19 Developing a Subsurface Investigation Plan ............................................................................. 21 3.3.1 Developing a Geophysical Testing Plan ............................................................................... 21

v 3.3.2 Selecting the Number and Locations for In Situ Tests, Drilling, and Sampling ................... 21 3.3.3 Determining the Minimum Depth of Investigation at Each Location ................................... 25 3.3.4 Determining the Required Types of Samples and Sampling Frequency ............................... 25 3.3.5 Developing an In Situ and Laboratory Testing Plan ............................................................. 26 3.3.6 Developing a Plan for Evaluating Groundwater Conditions ................................................. 33 Chapter 3 References ............................................................................................................................. 34 GEOPHYSICAL INVESTIGATIONS ............................................................................... 35 Introduction ............................................................................................................................... 35 Planning a Geophysical Investigation ....................................................................................... 36 Surface Geophysical Methods ................................................................................................... 36 4.3.1 Seismic Methods ................................................................................................................... 38 4.3.2 Electrical and Electromagnetic Methods ............................................................................... 45 4.3.3 Potential Field Methods ........................................................................................................ 50 Borehole Geophysical Methods ................................................................................................. 53 4.4.1 Borehole-to-Borehole and Surface-to-Borehole Methods .................................................... 54 4.4.2 In-Hole Logging Methods ..................................................................................................... 57 Chapter 4 References ............................................................................................................................. 64 IN SITU TESTING OF SOIL AND ROCK ....................................................................... 66 Introduction ............................................................................................................................... 66 Borehole Test Methods .............................................................................................................. 67 5.2.1 Standard Penetration Test ...................................................................................................... 67 5.2.2 Vane Shear Test .................................................................................................................... 72 5.2.3 Pressuremeter Testing ........................................................................................................... 75 Direct-Push In Situ Test Methods for Soils ............................................................................... 78 5.3.1 Cone-Penetration Testing ...................................................................................................... 78 5.3.2 Flat Plate Dilatometer Test .................................................................................................... 85 In Situ Tests for Rock ................................................................................................................ 88 5.4.1 Plate Load Tests on Rock ...................................................................................................... 88 5.4.2 Flat Jack Tests ....................................................................................................................... 89 5.4.3 Rock Dilatometer .................................................................................................................. 90 5.4.4 Large Field Direct Shear Test ............................................................................................... 90 5.4.5 Rock Borehole Shear Test ..................................................................................................... 90 5.4.6 Measurements for Rock Discontinuities ............................................................................... 91 Chapter 5 References ............................................................................................................................. 92 DRILLING AND SAMPLING OF SOIL AND ROCK .................................................... 94 Introduction ............................................................................................................................... 94 Field Equipment ........................................................................................................................ 94 6.2.1 Drilling on Land .................................................................................................................... 94 6.2.2 Drilling over Water ............................................................................................................... 95 Borehole Advancement Methods .............................................................................................. 96 6.3.1 Manual Methods .................................................................................................................... 96

vi 6.3.2 Test Pits ................................................................................................................................. 96 6.3.3 Auger Drilling ....................................................................................................................... 97 6.3.4 Rotary Drilling ...................................................................................................................... 98 6.3.5 Measuring While Drilling ..................................................................................................... 99 Soil Sampling .......................................................................................................................... 101 6.4.1 Split-Spoon (Disturbed Samples) ........................................................................................ 101 6.4.2 Direct-Push Sampling (Disturbed Samples) ....................................................................... 101 6.4.3 Thin-Wall Tube Sampling (Undisturbed Samples) ............................................................. 103 Rock Coring Methods .............................................................................................................. 108 6.5.1 Core Bits.............................................................................................................................. 108 6.5.2 Core Barrel Types ............................................................................................................... 109 6.5.3 Triple-Tube Core Barrel ...................................................................................................... 110 6.5.4 Logging Borings .................................................................................................................. 110 6.5.5 Soil Boring Logs ................................................................................................................. 111 6.5.6 Logging Rock Core ............................................................................................................. 113 6.5.7 Sample Protection ............................................................................................................... 114 Boring Closure ......................................................................................................................... 114 Chapter 6 References ........................................................................................................................... 116 HYDROGEOLOGIC CHARACTERIZATION ............................................................. 117 Introduction ............................................................................................................................. 117 Geology and Hydrogeology ..................................................................................................... 117 Aquifer Characteristics ............................................................................................................ 118 7.3.1 Hydraulic Conductivity ....................................................................................................... 118 7.3.2 Porosity ............................................................................................................................... 118 7.3.3 Permeability ........................................................................................................................ 118 7.3.4 Transmissivity ..................................................................................................................... 119 7.3.5 Storage Coefficient and Specific Yield ................................................................................ 119 Aquitard Characteristics .......................................................................................................... 119 Direction and Gradient of Groundwater Flow ......................................................................... 120 Groundwater Measurements .................................................................................................... 120 7.6.1 Methods for Groundwater Levels and Pressures ................................................................. 120 7.6.2 Methods for Aquifer Characteristics ................................................................................... 125 Chapter 7 References ........................................................................................................................... 129 LABORATORY TESTING OF SOIL AND ROCK ....................................................... 130 Introduction ............................................................................................................................. 130 Quality Assurance ................................................................................................................... 130 8.2.1 Sample Tracking ................................................................................................................. 131 8.2.2 Sample Transportation, Storage, and Handling ................................................................... 131 8.2.3 Sample Disturbance ............................................................................................................ 131 8.2.4 Assessment of Sample Disturbance .................................................................................... 133 Index Property Testing ............................................................................................................ 135 8.3.1 Particle Size Distribution .................................................................................................... 135

vii 8.3.2 Moisture Content ................................................................................................................. 136 8.3.3 Atterberg Limits .................................................................................................................. 136 8.3.4 Unit Weight ......................................................................................................................... 137 8.3.5 Specific Gravity .................................................................................................................. 138 8.3.6 Organic Content .................................................................................................................. 138 8.3.7 Electrical Resistivity ........................................................................................................... 138 8.3.8 pH Test ................................................................................................................................ 139 Soil Classification .................................................................................................................... 139 8.4.1 AASHTO Soil Classification System ................................................................................. 139 8.4.2 Unified Soil Classification System ..................................................................................... 141 8.4.3 Visual-Manual Procedure .................................................................................................... 143 8.4.4 Additional Tests for Soil Classification .............................................................................. 144 Compaction Tests .................................................................................................................... 145 Hydraulic Conductivity ........................................................................................................... 146 8.6.1 Flexible-Wall Permeameter ................................................................................................. 146 8.6.2 Rigid-Wall, Compaction-Mold Permeameter ..................................................................... 147 Consolidation ........................................................................................................................... 147 Shear Strength ......................................................................................................................... 149 8.8.1 Miniature Vane Test ............................................................................................................ 150 8.8.2 Direct Shear Test ................................................................................................................. 150 8.8.3 Triaxial Tests ....................................................................................................................... 150 8.8.4 Direct Simple Shear Test..................................................................................................... 154 8.8.5 Interpretation of Laboratory Strength Data ......................................................................... 154 Dynamic Properties ................................................................................................................. 155 8.9.1 Resonant Column Test ........................................................................................................ 155 8.9.2 Cyclic Triaxial Test ............................................................................................................. 156 8.9.3 Cyclic Direct Simple Shear Test ......................................................................................... 157 Laboratory Test Methods for Characterizing Subgrade Soils and Unbound Bases for Pavement Design ........................................................................................................................ 158 8.10.1 Resilient Modulus Test ................................................................................................... 158 8.10.2 California Bearing Ratio Test ......................................................................................... 158 8.10.3 Resistance-Value Test ..................................................................................................... 159 Laboratory Tests for Rock ....................................................................................................... 159 8.11.1 Moisture Content ............................................................................................................ 159 8.11.2 Unit Weight ..................................................................................................................... 160 8.11.3 Slake Durability of Weak Rock ...................................................................................... 160 8.11.4 Point-Load Strength Index .............................................................................................. 160 8.11.5 Direct Shear Test ............................................................................................................ 161 8.11.6 Compressive Strength and Elastic Moduli of Intact Rock Core Specimens ................... 161 Chapter 8 References ........................................................................................................................... 163 EVALUATION OF SOIL PROPERTIES ........................................................................ 164 Introduction ............................................................................................................................. 164 Stratigraphy ............................................................................................................................. 165 9.2.1 Geophysical Methods .......................................................................................................... 165

viii 9.2.2 In Situ Tests ......................................................................................................................... 166 9.2.3 Soil Borings ......................................................................................................................... 167 Soil Classification .................................................................................................................... 168 9.3.1 Soil Behavioral Type by Cone-Penetration Tests ............................................................... 168 9.3.2 Soil Classification by Flat Dilatometer Tests ...................................................................... 171 Soil Unit Weight ...................................................................................................................... 171 9.4.1 Unit Weight from Shear Wave Velocity ............................................................................. 172 9.4.2 Unit Weight from Cone Penetration Tests .......................................................................... 172 9.4.3 Unit Weight from Flat Dilatometer Tests ........................................................................... 173 Preconsolidation or Effective Yield Stress .............................................................................. 174 9.5.1 Effective Yield Stress from Cone-Penetration Tests ........................................................... 174 9.5.2 Effective Yield Stress from Flat Dilatometer Tests ............................................................ 176 9.5.3 Effective Yield Stress from Standard Penetration Tests ..................................................... 177 9.5.4 Effective Yield Stress from Shear Wave Velocity .............................................................. 178 Effective Stress Strength Parameters ....................................................................................... 179 9.6.1 Effective Strength Parameters from Cone-Penetration Tests .............................................. 179 9.6.2 Effective Strength Parameters from Flat Dilatometer Tests................................................ 182 9.6.3 Effective Strength Parameters from Standard Penetration Test .......................................... 184 Total Stress Strength Parameters ............................................................................................. 185 9.7.1 Undrained Shear Strength from Critical State Soil Mechanics ........................................... 185 9.7.2 Undrained Shear Strength from Cone-Penetration Tests .................................................... 186 9.7.3 Undrained Shear Strength from Flat Dilatometer Tests ...................................................... 187 9.7.4 Undrained Shear Strength from Standard Penetration Test ................................................ 187 9.7.5 Undrained Shear Strength from Vane Shear Tests, Pressuremeter Tests, and Other Tests 188 Lateral Stress State .................................................................................................................. 188 Modulus ................................................................................................................................... 189 9.9.1 Elastic Modulus from Shear Wave Velocity ....................................................................... 190 9.9.2 Elastic Modulus from Cone Penetration Test ..................................................................... 192 9.9.3 Elastic Modulus from Flat Dilatometer Tests ..................................................................... 193 9.9.4 Elastic Modulus from Standard Penetration Test ................................................................ 194 Rigidity Index .......................................................................................................................... 195 Flow Parameters ...................................................................................................................... 196 9.11.1 Coefficient of Consolidation from Piezocone Dissipation Tests .................................... 197 9.11.2 Coefficient of Consolidation from Dilatometer Dissipation Tests ................................. 199 9.11.3 Hydraulic Conductivity from Piezocone Dissipation Tests ............................................ 200 9.11.4 Hydraulic Conductivity Estimated from CPT Material Index ........................................ 201 Special Considerations ............................................................................................................ 202 Chapter 9 References ........................................................................................................................... 203 EVALUATION OF ROCK MASS PROPERTIES ......................................................... 206 Introduction ............................................................................................................................. 206 Intact Rock Classification ........................................................................................................ 207 Intact Rock Properties ............................................................................................................. 209 10.3.1 Specific Gravity of Solids ............................................................................................... 209

ix 10.3.2 Unit Weight ..................................................................................................................... 210 10.3.3 Seismic Velocities ........................................................................................................... 212 10.3.4 Uniaxial Compressive Strength ...................................................................................... 213 10.3.5 Elastic Modulus of Intact Rock ....................................................................................... 214 10.3.6 Poisson’s Ratio ............................................................................................................... 216 10.3.7 Tensile Strength .............................................................................................................. 216 10.3.8 Shear Strength of Intact Rock ......................................................................................... 217 Rock Mass Classification ........................................................................................................ 219 10.4.1 Rock Mass Rating ........................................................................................................... 219 10.4.2 Norwegian Geotechnical Institute Q-Rating System for Rock Masses .......................... 223 10.4.3 Geological Strength Index .............................................................................................. 224 10.4.4 Estimating Quality of Rock Mass from Seismic Velocity .............................................. 225 Rock Mass Parameters............................................................................................................. 226 10.5.1 Rock Mass Strength ........................................................................................................ 226 10.5.2 Rock Mass Modulus ....................................................................................................... 230 10.5.3 Foundation Bearing Resistances ..................................................................................... 231 10.5.4 Unit Side Resistance for Socketed Drilled Shafts ........................................................... 233 10.5.5 Rock Rippability and Earthwork Factor ......................................................................... 234 10.5.6 Other Rock Parameters ................................................................................................... 234 Chapter 10 References ......................................................................................................................... 236 COMPILING, REPORTING, AND PRESENTING GEOTECHNICAL INFORMATION ................................................................................................................. 238 Introduction ............................................................................................................................. 238 Uses of Geotechnical Information ........................................................................................... 238 Factual Information ................................................................................................................. 238 11.3.1 Preexisting Data Resources............................................................................................. 239 11.3.2 Remote Sensing Data ...................................................................................................... 239 11.3.3 Geophysical Information ................................................................................................ 239 11.3.4 In Situ Testing ................................................................................................................. 240 11.3.5 Hydrogeologic Information ............................................................................................ 240 11.3.6 Laboratory Testing .......................................................................................................... 240 11.3.7 Construction-Phase Testing and Monitoring Results ...................................................... 240 Interpretive Information .......................................................................................................... 240 11.4.1 Performance Criteria ....................................................................................................... 241 11.4.2 Ground Model ................................................................................................................. 241 11.4.3 Design Recommendations .............................................................................................. 241 11.4.4 Construction Considerations ........................................................................................... 242 11.4.5 Geotechnical Instrumentation and Monitoring ............................................................... 242 11.4.6 Geotechnical Information for LRFD .............................................................................. 243 Geotechnical Reports ............................................................................................................... 243 11.5.1 Uncertainty of Geotechnical Information ....................................................................... 244 11.5.2 Geotechnical Reports for Conventional Project Delivery Method ................................. 244 11.5.3 Geotechnical Reports for Alternative Project Delivery Method ..................................... 245 11.5.4 Geotechnical Data Reports ............................................................................................. 245 11.5.5 Geotechnical Baseline Report ......................................................................................... 246 11.5.6 Geotechnical Design Memoranda ................................................................................... 247

x Contractual Implications of Geotechnical Reports .................................................................. 248 11.6.1 Alternative Delivery Methods......................................................................................... 248 11.6.2 Contractor Briefings ....................................................................................................... 249 11.6.3 Legal Implications .......................................................................................................... 249 11.6.4 Differing Site Conditions Clause .................................................................................... 249 Chapter 11 References ......................................................................................................................... 250 APPENDIXES ............................................................................................................................251 A. Geotechnical Instrumentation ................................................................................................. 251 B. Applications of Geotechnical Instrumentation ........................................................................ 264 C. Evaluation of Existing Bridge Foundations for Reuse ............................................................ 272 D. Management of Geotechnical Data ......................................................................................... 282 E. Quality Assurance Systems ..................................................................................................... 310 F. Health and Safety .................................................................................................................... 317 G. Contracting Subsurface Investigations .................................................................................... 334 H. Technology Transfer Strategies .............................................................................................. 343

xi LIST OF TABLES Table 3-1. Geologic and man-made constraints Table 3-2. Performance issues and required design properties and parameters Table 3-3. Documents and sources of available information Table 3-4. Items that need to be evaluated during field reconnaissance Table 3-5. Guidelines for selecting number of investigation locations and depths of investigation Table 3-6. Investigation equipment and their applications Table 3-7. Summary of in situ tests and associated design parameters Table 3-8. Sampling equipment and their applications Table 3-9. Borehole advancing methods and their applications Table 3-10. Guidelines for selecting laboratory tests Table 4-1. Matrix of surface geophysical methods in relation to investigation objectives Table 4-2. ASTM guides and standards for surface geophysical investigations Table 4-3. Matrix of borehole geophysical methods in relation to investigation objectives Table 4-4. ASTM guides for borehole geophysical investigations Table 5-1. Summary of hammer energy measurements using automatic hammers Table 5-2. SPT correction factors for field procedures Table 5-3. Types of cone penetrometers Table 6-1. Rotary drill rigs Table 6-2. Standard drill rod sizes Table 6-3. Core sizes from WG swivel type double-tube core barrel Table 6-4. Basic rock types Table 6-5. Rated quality of rock mass based on RQD Table 7-1. Typical water level measurement intervals for observation wells Table 7-2. Methods for interpreting pumping tests Table 8-1. Specimen quality rating system based on vertical strain Table 8-2. Specimen quality rating system based on change in void ratio Table 8-3. Relationship between electric resistivity and corrosion potential Table 8-4. AASHTO soil classification system Table 8-5. Unified soil classification system Table 8-6. Soil constituents for visual-manual procedure Table 8-7. Checklist for visual-manual procedure Table 8-8. Summary of equipment and procedures for density tests Table 9-1. Methods for evaluating SBT from CPTs Table 9-2. Soil classification using the DMT Table 9-3. Relationships for constrained modulus from DMTs in various soil types Table 9-4. Expressions for estimating Gmax from DMT readings in various soils Table 10-1. Primary rock types classified by geologic origin and mineral grain size Table 10-2. Strength and stiffness properties of select intact rocks measured in laboratory tests Table 10-3. Selected guideline values of peak friction angles for rocks, joints, and minerals Table 10-4. Selected guideline values of residual friction angles for rocks Table 10-5. Assessment of discontinuity orientation for tunneling in fractured rock Table 10-6. RMR parameter R6 adjustment for orientation of discontinuities Table 10-7. Applicability of the Hoek-Brown model for intact and fractured rocks

xii Table 10-8. Values of the disturbance factor D for GSI rock mass quality system

xiii LIST OF FIGURES Figure 4-1. Typical ranges of compression (top) and shear wave velocity (bottom) Figure 4-2. Example seismic refraction tomography test results Figure 4-3. Estimated D8R ripper performance from seismic velocity Figure 4-4. Seismic reflection section showing depth to bedrock Figure 4-5. Seismic reflection section showing sinkhole locations Figure 4-6. Example Rayleigh-wave dispersion curve Figure 4-7. Example 2D shear wave velocity cross section from MASW test Figure 4-8. Typical ranges of electrical resistivity Figure 4-9. Example electrical resistivity imaging results Figure 4-10. Example terrain conductivity results Figure 4-11. Example GPR results showing base of fill layer Figure 4-12. Example GPR results showing pavement void detection Figure 4-13. Example of a microgravity profile Figure 4-14. Example of a microgravity contour map Figure 4-15. Example seismic crosshole data Figure 4-16. Example seismic downhole data Figure 4-17. Example mechanical caliper, natural gamma, and acoustic televiewer logs Figure 4-18. Example interpretation of acoustic televiewer log Figure 4-19. Example results from seismic logging Figure 5-1. Selection of in situ tests for geotechnical site characterization Figure 5-2. SPT setup and procedures Figure 5-3. Example of SPT N-values Figure 5-4. Comparison of (a) uncorrected (Nm) and (b) energy-corrected (N60) SPT blow counts Figure 5-5. VST or field van for clays and silts Figure 5-6. Limit equilibrium solutions for calculating undrained shear strength of rectangular and tapered vanes Figure 5-7. EVST results from selected depths in clay deposit Figure 5-8. Example of EVST in soft clay Figure 5-9. Basic components and procedures of the PMT Figure 5-10. Example PMT pressure-volume curve Figure 5-11. Basic setup and equipment for (electric) CPT Figure 5-12. Common piezocone configurations for pore pressure readings Figure 5-13. Example results from CPTu showing (a) total cone resistance, qt, (b) sleeve friction, fs, and (c) pore pressures, u2 Figure 5-14. Example piezo-dissipation tests from CPTu Figure 5-15. SCPTu Figure 5-16. Example SCPTu soundings in sediment Figure 5-17. Example continuous-interval SCPTu Figure 5-18. DMT procedures and measurement readings Figure 5-19. Example DMT measured pressure profiles Figure 5-20. Example DMT index profiles Figure 5-21. Example PLT on limestone Figure 5-22. Cross section of flat jack setup per ASTM D4729

xiv Figure 5-23. Rock borehole shear test in sandstone Figure 6-1. HSA methods: drill rod (left) and wireline (right) Figure 6-2. Rotary drilling techniques in comparison with other borehole methods Figure 6-3. Geometry of split-spoon sampler Figure 6-4. Direct-push samples of soil Figure 6-5. Example of recovered sonic soil samples Figure 6-6. Consecutive vibracore samples showing changes in stratigraphy Figure 6-7. Components of a fixed-piston sampler Figure 6-8. Osterberg piston sampler Figure 6-9. Denison triple-tube core barrel sampler Figure 6-10. Primary types of rock core barrels; (a) single tube; (b) rigid double tube; (c) swivel double tube; (d) triple tube Figure 6-11. Recovered rock core in gneissic granite bedrock Figure 6-12. Example engineering boring log Figure 6-13. Evaluation of RQD from recovered core Figure 7-1. Single-level monitoring well Figure 7-2. Multilevel monitoring wells Figure 7-3. Example potentiometric surface map Figure 7-4. Example results from pumping test in a confined aquifer Figure 7-5. Example results from slug test in an unconfined aquifer Figure 8-1. Changes in effective stress during drilling, sampling, and specimen preparation Figure 8-2. Example of x-ray radiography Figure 8-3. Example of particle-size distribution plot for a well-graded sand Figure 8-4. Atterberg limits Figure 8-5. AASHTO plasticity chart Figure 8-6. Plasticity chart Figure 8-7. Example of compaction curves Figure 8-8. Example results from CRS consolidation test Figure 8-9. Example of Casagrande procedure to estimate preconsolidation pressure Figure 8-10. Example DS test results Figure 8-11. (a) Schematic of triaxial apparatus and (b) assumed stress conditions for triaxial compression Figure 8-12. Example CU test results Figure 8-13. Example CD test results Figure 8-14. Example DSS test results Figure 8-15. Example results from a cyclic DSS test Figure 8-16. Example results from a cyclic triaxial test Figure 8-17. Schematic of the resilient modulus equipment Figure 8-18. Example results from DS test on rock with discontinuities Figure 9-1. Example subsurface profile developed from a 2D MASW survey Figure 9-2. Example subsurface profile developed from cone resistances of several CPT records Figure 9-3. Example subsurface profile developed from soil boring records and SPT values Figure 9-4. Nine-zone soil behavioral chart for conducting CPTs in soils Figure 9-5. Use of CPT material index Ic and algorithms for nine-zone soil behavioral chart Figure 9-6. Soil unit weight relationship with shear wave velocity

xv Figure 9-7. Soil unit weight estimated from CPT sleeve friction Figure 9-8. Soil unit weight estimated from DMT readings Figure 9-9. General relationship for effective yield stress and CPT net cone resistance in soils Figure 9-10. General trend for yield stress exponent and CPT material index Figure 9-11. General relationship for effective yield stress and DMT net contact pressure in soils Figure 9-12. General relationship for effective yield stress and energy-corrected SPT N60 resistance in soils Figure 9-13. General relationship for effective yield stress and shear wave velocity in soils Figure 9-14. Effective friction angle of sands from CPT-normalized cone resistance Figure 9-15. Effective stress friction angle of clays from CPTu via NTH solution Figure 9-16. Calibration of NTH solution with lab triaxial and in situ CPTu data from 105 clay sites Figure 9-17. Effective friction angle of sands from DMT horizontal stress index Figure 9-18. Calibration of NTH solution with lab triaxial and in situ DMT data from 46 clays Figure 9-19. Empirical relationship for effective friction angle of sands from stress-normalized SPT N60 value using data from undisturbed sampling techniques Figure 9-20. Normalized undrained shear strength ratio vs. OCR for clays tested in DSS mode Figure 9-21. Cone bearing factor Nkt for obtaining undrained shear strength in clays Figure 9-22. Trends reported between undrained shear strength and SPT resistance Figure 9-23. General relationships between K0 and OCR in soils for loading-unloading Figure 9-24. Representative stress-strain-strength curve of soil in triaxial compression mode Figure 9-25. Modulus reduction factor of sands and clays in drained and undrained loading expressed in terms of mobilized strength Figure 9-26. Dilatometer modulus vs. net cone resistance for different soils Figure 9-27. Estimate for Vs from SPT Figure 9-28. Geologic-specific relationship between equivalent elastic modulus and energy- corrected SPT N60 from DMTs and foundation performance Figure 9-29. Rigidity index from spherical cavity expansion (SCE-CSSM) in terms of ϕ and CPT resistances Figure 9-30. Representative monotonic dissipation record from CPTu2 in Mud Island Figure 9-31. Dissipation time factors from SCE-CSSM solution at different degrees of consolidation Figure 9-32. Definitions of monotonic vs. dilatory type for pore pressure response Figure 9-33. Correction of dilatory dissipation tests using square root time plots to get t50 Figure 9-34. Dissipations from DMT A-reading with time Figure 9-35. Interpreted coefficient of permeability from monotonic t50 dissipations in soils Figure 9-36. Coefficient of permeability expression from CPT material index in soils Figure 10-1. Diversity of rock types found in the conterminous United States. Note: each color represents one of 154 different geologic formations Figure 10-2. Geologic time scale and associated age of rocks Figure 10-3. Specific gravity of solids of common rock minerals Figure 10-4. Unit weight of saturated rock vs. porosity Figure 10-5. Trend for rock unit weight with in situ shear wave velocity Figure 10-6. Trends between measured Vs and Vp for various types of rocks Figure 10-7. Measured stress-strain response on intact gneissic rock

xvi Figure 10-8. General trends between tensile and compressive strengths for intact rock according to geologic origin Figure 10-9. General interrelationships between strength parameters of intact rock Figure 10-10. Basic components for RMR system Figure 10-11. New RMR component R23 = R2 + R3 for number of discontinuities Figure 10-12. Depictions of massive, favorable, unfavorable, and highly fractured rock mass scenarios for rock slope cuts Figure 10-13. Outline and components of the Q systems for RMR Figure 10-14. Chart for assessing the GSI rating and quality of rock masses Figure 10-15. Correlative trend for RMR in terms of shear wave velocity Figure 10-16. Example calculations of rock mass strength of marble using Hoek-Brown model Figure 10-17. Example rock mass strength of fractured marble from Hoek-Brown model to determine c' and ϕ' using (a) Mohr's circles and (b) MIT q-p' space Figure 10-18. Rock mass modulus estimated from the RMR and Q rating systems Figure 10-19. Allowable bearing stress for foundations on fractured rock Figure 10-20. Allowable bearing stress for drilled shaft foundations (L/d > 3) on rock Figure 10-21. Unit side resistance of drilled shaft foundations related to rock strength

xvii Author Acknowledgments The research presented in this report was conducted under National Cooperative Highway Research Program (NCHRP) 21-10 by Geosyntec Consultants, Inc. The principal investigators for the work were Mr. Njoroge Wainaina and Dr. Glenn J. Rix. The authors are grateful to the National Cooperative Highway Research Program of the National Academy of Sciences for their support. In particular, the authors would like to acknowledge the contributions and support provided by the NCHRP Project Managers Mr. David Reynaud and Dr. Waseem Dekelbab and the valuable guidance and peer review comments from the NCHRP Project Panel members.

xviii Abstract The primary purpose of geotechnical subsurface investigations in transportation projects is to collect data that will help transportation engineers and planners identify, assess, and address risks associated with subsurface conditions; select appropriate design parameters; and monitor performance during construction and operation phases of a project’s life cycle. The results of the research performed for NCHRP Project 21- 10 have resulted in a complete revision and update to the 1988 American Association of State Highway Transportation Officials (AASHTO) Manual on Subsurface Investigation that reflects the changes in the approaches and methods used for geotechnical site characterization that the geotechnical community has developed and adopted in the past 30 years. The updated manual provides information and guidelines to help geoprofessionals plan and execute a sound geotechnical site investigation program; use the results to develop a ground model for planning, design, construction, and asset management phases of a project; and report and document the results in a manner that facilitates peer review, communication with stakeholders, and potential future uses.

xix Summary Subsurface investigation plays a critical role in all phases of transportation project development— planning, design, construction, and operations—as it provides information that is needed to ensure public safety and to make cost-effective decisions. For the past 30 years, transportation engineers and planners have relied on the AASHTO Manual on Subsurface Investigation (1988) to provide guidance on best practices for planning and conducting geotechnical subsurface investigations. However, in the past 30 years, significant advances have occurred in the geophysical, in situ, and laboratory methods used by geoprofessionals to conduct subsurface investigations. There are also new design approaches (e.g., load and resistance factor design [LRFD]) and project delivery methods (e.g., design-build) that impact subsurface investigations. These changes in geotechnical practices, design approaches, and project delivery methods warrant an update to the AASHTO Manual on Subsurface Investigations to reflect the current state of the practice. The objective of the efforts to update the 1988 manual was to develop a concise, comprehensive document that will be invaluable for planning, executing, and using subsurface investigations and geotechnical characterizations for planning, designing, constructing, maintaining, and managing assets of transportation facilities. The organization of the updated AASHTO Manual on Subsurface Investigations was intended to mirror the manner in which a subsurface exploration program is typically performed. The major activities are as follows: • Planning the investigation (Chapters 2 and 3) • Executing the investigation (Chapters 4 through 8) • Interpreting the results of the investigation (Chapters 9 and 10) • Reporting and presenting the results of the investigation (Chapter 11) Supplemental information is presented in appendices that are broadly grouped into two categories— investigative and administrative. The following are new topics presented in the updated manual: • Geotechnical uncertainty and risk as they pertain to subsurface investigations • Developments in in situ test methods and their interpretation to estimate engineering properties of soil and rock • Rock mass characterization • Geotechnical reports for alternative project delivery methods • Geotechnical instrumentation • Geotechnical data management The results of the research performed for NCHRP Project 21-10 have resulted in a complete revision and update to the 1988 AASHTO Manual on Subsurface Investigation. The updated manual defines a reasonable minimum standard of practice for modern geotechnical site investigations and will enable geoprofessionals to develop cost-effective geotechnical design and construction solutions while optimizing project life-cycle costs, ensuring public safety and environmental sustainability, minimizing contract disputes and cost overruns, and accelerating construction.

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TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 258: Manual on Subsurface Investigations provides an update to the American Association of State Highway Transportation Officials (AASHTO) 1988 manual of the same name. This report reflects the changes in the approaches and methods used for geotechnical site characterization that the geotechnical community has developed and adopted in the past thirty years. The updated manual provides information and guidelines for planning and executing a geotechnical site investigation program. It may also be used to develop a ground model for planning, design, construction, and asset management phases of a project.

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