Geotechnical Engineering Principles and Practices of Soil Mechanics and Foundation Engineering V. N. S. Murthy Consulting Geotechnical Engineer Bangalore, India MARCEL DEKKER, INC. NEW YORK • BASEL CONTENTS Foreword Mark T. Bowers v Foreword Bengt B. Broms vii Preface ix CHAPTER 1 INTRODUCTION 1 1.1 General Remarks 1 1.2 A Brief Historical Development 2 1.3 Soil Mechanics and Foundation Engineering 3 CHAPTER 2 SOIL FORMATION AND CHARACTERIZATION 5 2.1 Introduction 5 2.2 Rock Classification 5 2.3 Formation of Soils 7 2.4 General Types of Soils 7 2.5 Soil Particle Size and Shape 9 2.6 Composition of Clay Minerals 11 2.7 Structure of Clay Minerals 11 2.8 Clay Particle-Water Relations 14 2.9 Soil Mass Structure 17 XI x» Contents CHAPTER 3 SOIL PHASE RELATIONSHIPS, INDEX PROPERTIES AND CLASSIFICATION 19 3.1 Soil Phase Relationships 19 3.2 Mass-Volume Relationships 20 3.3 Weight-Volume Relationships 24 3.4 Comments on Soil Phase Relationships 25 3.5 Index Properties of Soils 31 3.6 The Shape and Size of Particles 32 3.7 Sieve Analysis 33 3.8 The Hydrometer Method of Analysis 35 3.9 Grain Size Distribution Curves 43 3.10 Relative Density of Cohesionless Soils 44 3.11 Consistency of Clay Soil 45 3.12 Determination of Atterberg Limits 47 3.13 Discussion on Limits and Indices 52 3.14 Plasticity Chart 59 3.15 General Considerations for Classification of Soils 67 3.16 Field Identification of Soils 68 3.17 Classification of Soils 69 3.18 Textural Soil Classification 69 3.19 AASHTO Soil Classification System 70 3.20 Unified Soil Classification System (USCS) 73 3.21 Comments on the Systems of Soil Classification 76 3.22 Problems' 80 CHAPTER 4 SOIL PERMEABILITY AND SEEPAGE 87 4.1 Soil Permeability 87 4.2 Darcy's Law 89 4.3 Discharge and Seepage Velocities 90 4.4 Methods of Determination of Hydraulic Conductivity of Soils 91 4.5 Constant Head Permeability Test 92 4.6 Falling Head Permeability Test 93 4.7 Direct Determination of k of Soils in Place by Pumping Test 97 4.8 Borehole Permeability Tests 101 4.9 Approximate Values of the Hydraulic Conductivity of Soils 102 4.1Q Hydraulic Conductivity in Stratified Layers of Soils 102 4.11 Empirical Correlations for Hydraulic Conductivity 103 4.12 Hydraulic Conductivity of Rocks by Packer Method 112 4.13 Seepage 114 4.14 Laplace Equation 114 Contents xiii 4.15 Flow Net Construction 116 4.16 Determination of Quantity of Seepage 120 4.17 Determination of Seepage Pressure 122 4.18 Determination of Uplift Pressures 123 4.19 Seepage Flow Through Homogeneous Earth Dams 126 4.20 Flow Net Consisting of Conjugate Confocal Parabolas 127 4.21 Piping Failure 131 4.22 Problems 138 CHAPTER 5 EFFECTIVE STRESS AND PORE WATER PRESSURE 143 5.1 Introduction 143 5.2 Stresses when No Flow Takes Place Through the Saturated Soil Mass 145 5.3 Stresses When Flow Takes Place Through the Soil from Top to Bottom 146 5.4 Stresses When Flow Takes Place Through the Soil from Bottom to Top 147 5.5 Effective Pressure Due to Capillary Water Rise in Soil 149 5.6 Problems 170 CHAPTER 6 STRESS DISTRIBUTION IN SOILS DUE TO SURFACE LOADS 173 '6.1 Introduction 173 6.2 Boussinesq's Formula for Point Loads 174 6.3 Westergaard's Formula for Point Loads 175 6.4 Line Loads 178 6.5 Strip Loads 179 6.6 Stresses Beneath the Corner of a Rectangular Foundation 181 6.7 Stresses Under Uniformly Loaded Circular Footing 186 6.8 Vertical Stress Beneath Loaded Areas of Irregular Shape 188 6.9 Embankment Loadings 191 6.10 Approximate Methods for Computing az 197 6.11 Pressure Isobars 198 6.12 Problems . 203 CHAPTER 7 COMPRESSIBILITY AND CONSOLIDATION 207 7.1 Introduction 207 7.2 Consolidation 208 7.3 Consolidometer 212 xiv Contents 7.4 The Standard One-Dimensional Consolidation Test 213 7.5 Pressure-Void Ratio Curves 214 7.6 Determination of Preconsolidation Pressure 218 7.7 e-logp Field Curves for Normally Consolidated and Overconsolidated Clays of Low to Medium Sensitivity 219 7.8 Computation of Consolidation Settlement 219 7.9 Settlement Due to Secondary Compression 224 7.10 Rate of One-dimensional Consolidation Theory of Terzaghi 233 7.11 Determination of the Coefficient of Consolidation 240 7.12 Rate of Settlement Due to Consolidation 242 7.13 Two- and Three-dimensional Consolidation Problems 243 7.14 Problems 247 CHAPTER 8 SHEAR STRENGTH OF SOIL 253 8.1 Introduction 253 8.2 Basic Concept of Shearing Resistance and Shearing Strength 253 8.3 The Coulomb Equation 254 8.4 Methods of Determining Shear Strength Parameters 255 8.5 Shear Test Apparatus 256 8.6 Stress Condition at a Point in a Soil Mass 260 8.7 Stress Conditions in Soil During Triaxial Compression Test 262 8.8 Relationship Between the Principal Stresses and Cohesion c 263 8.9 Mohr Circle of Stress 264 8.10 Mohr Circle of Stress When a Prismatic Element is Subjected to Normal and Shear Stresses 265 8.11 Mohr Circle of Stress for a Cylindrical Specimen Compression Test 266 8.12 Mohr-Coulomb Failure Theory 268 8.13 Mohr Diagram for Triaxial Compression Test at Failure 269 8.14 Mohr Diagram for a Direct Shear Test at Failure 270 8.15 Effective Stresses 274 8.16 Shear Strength Equation in Terms of Effective Principal Stresses 275 8.17 Stress-Controlled and Strain-Controlled Tests 276 8.18 Types of Laboratory Tests 276 8.19 Shearing Strength Tests on Sand . 278 8.20 Unconsolidated-Undrained Test 284 8.21 Unconfined Compression Tests 286 8.22 Consolidated-Undrained Test on Saturated Clay 294 8.23 Consolidated-Drained Shear Strength Test 296 8.24 Pore Pressure Parameters Under Undrained Loading 298 8.25 Vane Shear Tests 300 Contents xv 8.26 Other Methods for Determining Undrained Shear Strength of Cohesive Soils 302 8.27 The Relationship Between Undrained Shear Strength and Effective Overburden Pressure 304 8.28 General Comments 310 8.29 Questions and Problems 311 CHAPTER 9 SOIL EXPLORATION 317 9.1 Introduction 317 9.2 Boring of Holes 318 9.3 Sampling in Soil 322 9.4 Rock Core Sampling 325 9.5 Standard Penetration Test 327 9.6 SPT Values Related to Relative Density of Cohesionless Soils 330 9.7 SPT Values Related to Consistency of Clay Soil 330 9.8 Static Cone Penetration Test (CPT) 332 9.9 Pressuremeter 343 9.10 The Flat Dilatometer Test .349 9.11 Field Vane Shear Test (VST) 3 51 9.12 Field Plate Load Test (PLT) 3 51 9.13 Geophysical Exploration 352 9.14 Planning of Soil Exploration 358 9.15 Execution of Soil Exploration Program 359 9.16 Report ' 361 9.17 Problems 362 CHAPTER 10 STABILITY OF SLOPES 365 10.1 Introduction 365 10.2 General Considerations and Assumptions in the Analysis 367 10.3 Factor of Safety 368 10.4 Stability Analysis of Infinite Slopes in Sand 371 10.5 Stability Analysis of Infinite Slopes in Clay 372 10.6 Methods of Stability Analysis of Slopes of Finite Height 376 10.7 Plane Surface of Failure . 376 10.8 Circular Surfaces of Failure 378 10.9 Failure Under Undrained Conditions (</>u = 0) 380 10.10 Friction-Circle Method 382 10.11 Taylor's Stability Number 389 10.12 Tension Cracks 393 10.13 Stability Analysis by Method of Slices for Steady Seepage 393 xvi Contents 10.14 Bishop's Simplified Method of Slices 400 10.15 Bishop and Morgenstern Method for Slope Analysis 403 10.16 Morgenstern Method of Analysis for Rapid Drawdown Condition 405 10.17 Spencer Method of Analysis 408 10.18 Problems 411 CHAPTER 11 LATERAL EARTH PRESSURE 419 11.1 Introduction 419 11.2 Lateral Earth Pressure Theory 420 11.3 Lateral Earth Pressure for at Rest Condition 421 11.4 Rankine's States of Plastic Equilibrium for Cohesionless Soils 425 11.5 Rankine's Earth Pressure Against Smooth Vertical Wall with Cohesionless Backfill 428 11.6 Rankine's Active Earth Pressure with Cohesive Backfill 440 11.7 Rankine's Passive Earth Pressure with Cohesive Backfill 449 11.8 Coulomb's Earth Pressure Theory for Sand for Active State 452 11.9 Coulomb's Earth Pressure Theory for Sand for Passive State 455 11.10 Active Pressure by Culmann's Method for Cohesionless Soils 456 11.11 Lateral Pressures by Theory of Elasticity for Surcharge Loads on the Surface of Backfill 458 11.12 Curved Surfaces of Failure for Computing Passive Earth Pressure 462 11.13 Coefficients of Passive Earth Pressure Tables and Graphs 464 11.14 Lateral Earth Pressure on Retaining Walls During Earthquakes 467 11.15 Problems 476 CHAPTER 12 SHALLOW FOUNDATION I: ULTIMATE BEARING CAPACITY 481 12.1 Introduction 481 12.2 The Ultimate Bearing Capacity of Soil 483 12.3 Some of the Terms Defined 483 12.4 Types of Failure in Soil 485 12.5 An Overview of Bearing Capacity Theories 487 12.6 Terzaghi's Bearing Capacity Theory 488 12.7 Skempton's Bearing Capacity Factor TV. 493 12.8 Effect of Water Table on Bearing Capacity 494 12.9 The General Bearing Capacity Equation 503 12.10 Effect of Soil Compressibility on Bearing Capacity of Soil 509 12.11 Bearing Capacity of Foundations Subjected to Eccentric Loads 515 12.12 Ultimate Bearing Capacity of Footings Based on SPT Values (AO 518 12.13 The CPT Method of Determining Ultimate Bearing Capacity 518 Contents xvii 12.14 Ultimate Bearing Capacity of Footings Resting on Stratified Deposits of Soil 521 12.15 Bearing Capacity of Foundations on Top of a Slope 529 12.16 Foundations on Rock 532 12.17 Case History of Failure of the Transcona Grain Elevator 533 12.18 Problems 536 CHAPTER 13 SHALLOW FOUNDATION II: SAFE BEARING PRESSURE AND SETTLEMENT CALCULATION 545 13.1 Introduction 545 13.2 Field Plate Load Tests 548 13.3 Effect of Size of Footings on Settlement 554 13.4 Design Charts from SPT Values for Footings on Sand 555 13.5 Empirical Equations Based on SPT Values for Footings on Cohesionless Soils 558 13.6 Safe Bearing