Fundamentals of Soil Mechanics for Sedimentary and Residual Soils Book

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 CaseA: 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 190

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 Parameter 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 Modules 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