Fundamentals of Soil Mechanics for Sedimentary and Residual Soils

CONTENTS

PREFACE xv

ACKNOWLEDGMENTS xix

1 SOIL FORMATION, COMPOSITION, AND BASIC CONCEPTS 1

1.1 Weathering Processes, Sedimentary and Residual Soils / 1

1.2 Clay Minerals / 3

1.3 Influence of Topography on Weathering Processes / 5

1.4 Factors Governing the Properties of Sedimentary and Residual Soils / 6

1.5 Remolded, or Destructured, Soils / 10

References / 11

2 BASIC DEFINITIONS AND PHASE RELATIONSHIPS 13

2.1 Components of Soil / 13

2.2 Phase Relationships / 14

2.3 Examples in Use of Phase Relationships / 17

2.4 Measurement of Basic Properties / 22

2.4.1 Bulk Density / 22

2.4.2 Water Content / 22

2.4.3 Solid Density and Specific Gravity / 22

Exercises / 24

3 BASIC INDEX TESTS, SOIL CLASSIFICATION AND DESCRIPTION 27

3.1 General / 27

3.1.1 Gravel and Sand / 27

3.1.2 Clay / 28

3.1.3 Silt / 28

3.2 Particle Size and Its Role in Influencing Properties / 28

3.2.1 Measurement of Particle Size / 29

3.3 Plasticity and Atterberg Limits / 31

3.3.1 Determination of Atterberg Limits / 31

3.4 Liquidity Index of Clay and Relative Density of Sand / 35

3.5 Sensitivity, Thixotropy, and Activity of Clays / 36

3.6 Systematic Classification Systems / 37

3.6.1 Unified Soil Classification System / 38

3.6.2 Additional Notes Regarding Classification / 40

3.6.3 Description of In situ (Undisturbed) Characteristics of Soil / 42

3.7 Classification of Residual Soils / 44

3.7.1 Parent Rock / 45

3.7.2 Usefulness of Existing Systems / 45

3.7.3 Classification of Weathering Profile / 46

3.7.4 Importance of Mineralogy and Structure / 47

References / 48

4 STRESS AND PORE PRESSURE STATE IN THE GROUND 49

4.1 Vertical Stress in the Ground / 49

4.2 Pore Pressures above Water Table and Seasonal Variations / 50

4.2.1 Case A: Coarse-Grained Soils / 52

4.2.2 Case B: Low-Permeability Clays / 53

4.2.3 Case C: Medium- to High-Permeability Clays / 53

4.3 Hill Slopes, Seepage, and Pore Pressures / 55

4.4 Significance of the Water Table (or Phreatic Surface) / 56

4.5 Horizontal Stress in Ground / 57

4.6 Worked Examples / 60

4.6.1 Worked Example 1 / 60

4.6.2 Worked Example 2 / 62

References / 64

Exercises / 64

5 STRESSES IN THE GROUND FROM APPLIED LOADS 67

5.1 General / 67

5.2 Elastic Theory Solutions for Stresses Beneath Loaded Areas / 68

References / 74

Exercises / 75

6 PRINCIPLE OF EFFECTIVE STRESS 77

6.1 The Basic Principle / 77

6.2 Applied Stresses, Drained and Undrained Behavior / 80

6.3 Pore Pressure Changes Under Undrained Conditions / 81

6.4 Some Practical Implications of the Principle of Effective Stress / 83

6.4.1 Stress State on Soil Element Below Submerged Surface (Bed of Lake or Seabed) / 83

6.4.2 Force Resisting Sliding of Concrete Gravity Dam / 84

6.4.3 Influence of Rainfall on Slope Stability / 85

6.4.4 Ground Settlement Caused By Lowering Water Table / 86

References / 87

7 PERMEABILITY AND SEEPAGE 89

7.1 General / 89

7.2 Pressure, “Head,” and Total Head / 90

7.3 Darcy’s Law / 92

7.3.1 Notes on Darcy’s Law / 92

7.3.2 Note on Seepage Velocity / 92

7.4 Measurement of Permeability / 93

7.5 General Expression for Seepage in a Soil Mass / 95

7.6 Steady-State Flow, Laplace Equation, and Flow Nets / 97

7.6.1 Flow nets—Conventions Used in Their Construction / 99

7.6.2 Boundary Conditions for Flow Nets / 100

7.6.3 Methods for Solution of Flow Nets / 101

7.6.4 Basic Requirements of Flow Net and Rules for Hand Sketching Flow Nets / 102

7.6.5 Use of Flow Nets for Practical Purposes / 103

7.7 Critical Hydraulic Gradient (and “Quicksand”) / 104

7.7.1 Quicksand / 106

7.7.2 Worked Example / 106

7.8 Unconfined Flow Nets and Approximations in Conventional Formulation / 108

7.9 Use of Filters in Designed Structures / 109

7.10 Vertical Flow Through Single Layers and Multilayers / 111

7.11 Note on Groundwater Studies and Groundwater Mechanics / 113

7.12 Flow into Excavations, Drains, and Wells / 115

References / 117

Exercises / 117

8 COMPRESSIBILITY, CONSOLIDATION, AND SETTLEMENT 121

8.1 General Concepts / 121

8.2 Estimation of Settlement Using Elasticity Theory / 122

8.2.1 Drained and Undrained Behavior / 123

8.2.2 Limitations of Elasticity Theory / 124

8.3 Estimation of Settlement Assuming 1-D Behavior / 124

8.4 Immediate (“Elastic”) Settlement and Long-Term (Consolidation) Settlement / 126

8.4.1 Immediate and Consolidation Settlement in Sands / 126

8.4.2 Immediate and Consolidation Settlement in Clays / 126

8.5 Consolidation Behavior of Clays (and Silts) / 129

8.5.1 Odometer Test / 129

8.5.2 Consolidation Characteristics—Magnitude / 130

8.5.3 Consolidation Behavior–Time Rate / 142

8.6 Estimation of Settlement from Odometer Test Results / 154

8.6.1 Settlement of a Building Foundation / 154

8.6.2 Settlement of Fill on Soft Clay / 160

8.7 Approximations and Uncertainties in Settlement Estimates Based on Odometer Tests / 165

8.7.1 Interpretation of Void Ratio–Stress Curves and Sample Disturbance / 165

8.7.2 Assumptions Regarding Pore Pressure State / 167

8.7.3 Lateral Deformation / 168

8.7.4 Submergence of Fill Loads / 168

8.7.5 Use of Terzaghi Theory of Consolidation for Nonlinear Soils / 168

8.7.6 Influence of Inadequate Data on Actual Soil Conditions / 169

8.8 Allowable Settlement / 170

8.8.1 Total (or Absolute) Settlement / 170

8.8.2 Relative Movement between Structure and Surrounding Ground / 170

8.8.3 Differential Settlement of Buildings / 170

8.9 Radial Flow and Sand (or “Wick”) Drains / 172

8.9.1 Theory for Design of Sand and Wick Drains / 173

8.10 Settlement of Foundations on Sand / 174

8.10.1 Schmertman Method Using Static Cone Penetrometer Results / 175

8.10.2 Burland and Burbidge Method / 176

8.10.3 Worked Example / 178

References / 181

Exercises / 182

9 SHEAR STRENGTH OF SOILS 185

9.1 Basic Concepts and Principles / 185

9.1.1 General Expression for Shear Strength / 186

9.1.2 Undrained Shear Strength (su ) / 187

9.1.3 Relationship between Strength in Terms of Effective Stress and Undrained Strength / 187

9.2 Measurement of Shear Strength / 190

9.2.1 Direct Shear Test (or Shear Box Test) / 190

9.2.2 Triaxial Test / 191

9.2.3 Mohr’s Circle of Stress / 193

9.2.4 Use of Mohr’s Circle for Plotting Triaxial Test Results / 195

9.2.5 Soil Behavior in Consolidated Undrained and Drained Tests / 197

9.2.6 Area Correction in Triaxial Tests / 199

9.2.7 Failure Criteria in Terms of Principal Stresses / 200

9.2.8 Determination of Angle of Failure Plane / 201

9.2.9 Worked Example / 201

9.3 Practical Use of Undrained Strength and Effective Strength Parameters / 203

9.4 Shear Strength and Deformation Behavior of Sand / 204

9.5 Residual Strength of Clays / 206

9.5.1 Measurement of Residual Strength / 208

9.6 Stress Path Concept / 209

9.7 Pore Pressure Parameters A and B / 211

9.8 Shear Strength and Deformation Behavior of Clay / 212

9.8.1 Behavior of Fully Remolded Clay / 212

9.8.2 Behavior of Undisturbed Sedimentary Clays / 214

9.8.3 Behavior of Residual Soils / 221

9.8.4 Failure Criterion and Determination of c_ and φ from Consolidated Undrained Tests / 224

9.9 Typical Values of Effective Strength Parameters for Clays and Silts and Correlations with Other Properties / 225

9.10 Undrained Strength of Undisturbed and Remolded Soils / 228

9.10.1 Sedimentary Clays / 228

9.10.2 Remolded Soils / 230

9.10.3 Residual Soils / 231

9.11 Measurement of Undrained Shear Strength / 232

9.11.1 Unconfined Compression test / 232

9.11.2 Vane Test / 232

References / 232

Exercises / 233

10 SITE INVESTIGATIONS, FIELD TESTING, AND PARAMTER CORRELATIONS 235

10.1 Overview / 235

10.2 Drilling / 235

10.2.1 Hand Auguring / 236

10.2.2 Machine Drilling / 236

10.2.3 Continuous Coring with Single-Tube Core Barrel (Also Known as Open Barrel) / 238

10.2.4 Rotary Drilling Using Core Barrels / 238

10.2.5 Wash Drilling / 239

10.2.6 Percussion Boring / 239

10.3 Undisturbed Sampling Using Sample Tubes / 239

10.4 Block Sampling / 241

10.5 Investigation Pits (or Test Pits) / 242

10.6 In Situ Testing / 242

10.6.1 Limitations of Drilling and Undisturbed Sampling / 242

10.6.2 Standard Penetration Test (Dynamic Test) / 243

10.6.3 Dutch Static Cone Penetration Test CPT / 246

10.6.4 Shear Vane Test / 249

10.7 Correlations between In Situ Test Results and Soil Properties / 250

10.7.1 SPT N Values and CPT Values / 250

10.7.2 Undrained Shear Strength of Clay / 251

10.7.3 Relative Density of Sand / 252

10.7.4 Stiffness Modulus of Sand / 253

References / 254

11 STABILITY CONCEPTS AND FAILURE MECHANISMS 257

11.1 Basic Concepts / 257

11.2 Stability of Slopes / 259

11.3 Bearing Capacity / 261

11.4 Retaining Walls / 262

11.5 Further Observations / 264

11.5.1 Safety Factors, Load Factors, and Strength Reduction Factors / 264

11.5.2 Questions of Deformation Versus Stability / 264

References / 265

12 BEARING CAPACITY AND FOUNDATION DESIGN 267

12.1 Bearing Capacity / 267

12.1.1 Bearing Capacity in Terms of Effective Stress / 270

12.1.2 Bearing Capacity in Terms of Total Stress (Undrained Behavior) / 270

12.1.3 Eccentric and Inclined Loads / 270

12.2 Shallow Foundations on Clay / 272

12.2.1 Use of Undrained Shear Strength / 272

12.2.2 Application of Factor of Safety / 272

12.2.3 Bearing Capacity Versus Settlement Tolerance in Design of Foundations / 273

12.2.4 Worked Examples / 274

12.3 Shallow Foundations on Sand / 276

12.3.1 Use of Bearing Capacity Theory / 276

12.3.2 Empirical Methods for Foundations on Sand / 277

12.4 Pile Foundations / 278

12.4.1 Basic Concepts and Pile Types / 278

12.4.2 Pile-Bearing Capacity—Basic Formula and Methods of Estimation / 281

12.4.3 Bearing Capacity of Piles in Clay / 282

12.4.4 Bearing Capacity of Piles in Sand / 285

12.4.5 Pile Group Behavior / 286

12.4.6 Lateral Load Capacity of Piles / 289

References / 303

Exercises / 304

13 EARTH PRESSURE AND RETAINING WALLS 307

13.1 Coulomb Wedge Analysis / 307

13.2 At-Rest Pressure, Active Pressure, Passive Pressure, and Associated Deformations / 312

13.3 Rankine Earth Pressures / 312

13.4 Influence of Wall Friction / 316

13.5 Earth Pressure Coefficients / 316

13.6 Total Stress Analysis / 317

13.7 Maximum Height of Unsupported Vertical Banks or Cuts / 317

13.8 Construction Factors Influencing Earth Pressures on Retaining Walls / 319

13.9 Propped (Strutted) Trenches / 321

13.10 Retaining-Wall Design Example / 322

13.11 Sheet Pile (and Similar) Retaining Walls / 329

13.11.1 FreeStanding and Propped Cantilever Walls / 329

13.12 Reinforced-Earth Walls / 337

13.12.1 Concept and General Behavior / 337

13.12.2 Reinforcement Types / 338

13.12.3 Basic Design Procedures / 339

13.12.4 Other Matters / 349

References / 351

Exercises / 351

14 STABILITY OF SLOPES 355

14.1 Introduction / 355

14.2 Analysis Using Circular Arc Failure Surfaces / 357

14.2.1 Circular Arc Analysis Using Total Stresses / 359

14.2.2 Circular Arc Analysis in Terms of Effective Stresses / 360

14.2.3 Example Calculation Using Bishop Method / 362

14.2.4 Bishop’s Method for Submerged Slopes / 363

14.3 Stability Analysis of Infinite Slopes / 366

14.4 Short- and Long-Term Stability of Built Slopes / 368

14.4.1 Excavated Slopes / 369

14.4.2 Embankments on Soft Clays / 371

14.5 Stability Analysis for Earth Dams / 377

14.5.1 Estimation of Pore-Water Pressures During or at End of Construction / 377

14.5.2 Full-Reservoir Steady-State Seepage Condition / 379

14.5.3 Rapid Drawdown Pore Pressures / 380

14.6 Influence of Climate and Weather on Stability of Slopes / 381

14.7 Stability Analysis Using Noncircular Failure Surfaces / 385

References / 387

Exercises / 387

15 SOIL COMPACTION 391

15.1 Earthworks and Soil Compaction / 391

15.2 Compaction Behavior of Soils / 391

15.3 Control of Compaction / 397

15.3.1 Traditional Method of Compaction Control / 397

15.3.2 Alternative Compaction Control Based on Undrained Shear Strength and Air Voids / 397

15.4 Difficulties in Compacting Clays / 401

15.4.1 Soils Considerably Wetter Than Optimum Water Content / 401

15.4.2 Soils That Soften During Compaction / 401

15.5 Compaction of Granular and Non-Plastic Materials / 402

References / 404

16 SPECIAL SOIL TYPES 405

16.1 General Comments / 405

16.2 Partially Saturated Soils / 406

16.2.1 Occurrence / 406

16.2.2 Measurements of Degree of Saturation / 407

16.2.3 Mechanics of Partially Saturated Soils / 408

16.3 Expansive or Swelling Clays / 415

16.3.1 Basic Concepts of Expansive Behavior / 415

16.3.2 Estimation of Swelling Pressure and Swell Magnitude / 416

16.3.3 Estimation of Swell Magnitude / 420

16.4 Collapsing Soils / 421

References / 424

INDEX 425