Soil Strength and Slope Stability

Soil Strength and Slope Stability, Second Edition presents the latest thinking and techniques in the assessment of natural and man-made slopes, and the factors that cause them to survive or crumble. Using clear, concise language and practical examples, the book explains the practical aspects of geotechnical engineering as applied to slopes and embankments. The new second edition includes a thorough discussion on the use of analysis software, providing the background to understand what the software is doing, along with several methods of manual analysis that allow readers to verify software results. The book also includes a new case study about Hurricane Katrina failures at 17^th Street and London Avenue Canal, plus additional case studies that frame the principles and techniques described.

Slope stability is a critical element of geotechnical engineering, involved in virtually every civil engineering project, especially highway development. Soil Strength and Slope Stability fills the gap in industry literature by providing practical information on the subject without including extraneous theory that may distract from the application. This balanced approach provides clear guidance for professionals in the field, while remaining comprehensive enough for use as a graduate-level text. Topics include:

• Mechanics of soil and limit equilibrium procedures
• Analyzing slope stability, rapid drawdown, and partial consolidation
• Safety, reliability, and stability analyses
• Reinforced slopes, stabilization, and repair

The book also describes examples and causes of slope failure and stability conditions for analysis, and includes an appendix of slope stability charts. Given how vital slope stability is to public safety, a comprehensive resource for analysis and practical action is a valuable tool. Soil Strength and Slope Stability is the definitive guide to the subject, proving useful both in the classroom and in the field.

J. MICHAEL DUNCAN is University Distinguished Professor Emeritus of Civil and Environmental Engineering, and Co-Director of the Center for Geotechnical Practice and Research (CGPR) at Virginia Tech in Blacksburg, Virginia.

STEPHEN G. WRIGHT is a professor emeritus of Geotechnical Engineering in the Department of Civil, Architectural, and Environmental Engineering at the University of Texas at Austin.

THOMAS L. BRANDON is an associate professor of Civil and Environmental Engineering and Director of the W. C. English Geotechnical Research Laboratory at Virginia Tech in Blacksburg, Virginia.

Foreword ix

Preface xi

Chapter 1 Introduction 1

Summary 3

Chapter 2 Examples and Causes Of Slope Failures 5

2.1 Introduction 5

2.2 Examples of Slope Failure 5

2.3 The Olmsted Landslide 11

2.4 Panama Canal Landslides 12

2.5 The Rio Mantaro Landslide 12

2.6 Kettleman Hills Landfill Failure 13

2.7 Causes of Slope Failure 13

2.8 Summary 17

Chapter 3 Soil Mechanics Principles 19

3.1 Introduction 19

3.2 Total and Effective Stresses 20

3.3 Drained and Undrained Shear Strengths 21

3.4 Basic Requirements for Slope Stability Analyses 26

Chapter 4 Stability Conditions for Analysis 31

4.1 Introduction 31

4.2 End-of-Construction Stability 31

4.3 Long-Term Stability 32

4.4 Rapid (Sudden) Drawdown 32

4.5 Earthquake 33

4.6 Partial Consolidation and Staged Construction 33

4.7 Other Loading Conditions 34

4.8 Analysis Cases for Earth and Rockfill Dams 34

Chapter 5 Shear Strength 37

5.1 Introduction 37

5.2 Behavior of Granular Materials—Sand, Gravel, and Rockfill 37

5.3 Silts 52

5.4 Clays 57

5.5 Municipal Solid Waste 78

Chapter 6 Mechanics of Limit Equilibrium Procedures 81

6.1 Definition of the Factor of Safety 81

6.2 Equilibrium Conditions 82

6.3 Single Free-Body Procedures 82

6.4 Procedures of Slices: General 87

6.5 Procedures of Slices: Circular Slip Surfaces 87

6.6 Procedures of Slices: Noncircular Slip Surfaces 94

6.7 Procedures of Slices: Assumptions, Equilibrium Equations, and Unknowns 105

6.8 Procedures of Slices: Representation of Interslice Forces (Side Forces) 105

6.9 Computations with Anisotropic Shear Strengths 112

6.10 Computations with Curved Strength Envelopes 112

6.11 Finite Element Analysis of Slopes 112

6.12 Alternative Definitions of the Factor of Safety 113

6.13 Pore Water Pressure Representation 116

Chapter 7 Methods of Analyzing Slope Stability 125

7.1 Simple Methods of Analysis 125

7.2 Slope Stability Charts 126

7.3 Spreadsheet Software 128

7.4 Finite Element Analyses of Slope Stability 129

7.5 Computer Programs for Limit Equilibrium Analyses 130

7.6 Verification of Results of Analyses 132

7.7 Examples for Verification of Stability Computations 134

Chapter 8 Reinforced Slopes and Embankments 159

8.1 Limit Equilibrium Analyses with Reinforcing Forces 159

8.2 Factors of Safety for Reinforcing Forces and Soil Strengths 159

8.3 Types of Reinforcement 160

8.4 Reinforcement Forces 161

8.5 Allowable Reinforcement Forces and Factors of Safety 162

8.6 Orientation of Reinforcement Forces 163

8.7 Reinforced Slopes on Firm Foundations 164

8.8 Embankments on Weak Foundations 164

Chapter 9 Analyses for Rapid Drawdown 169

9.1 Drawdown during and at the End of Construction 169

9.2 Drawdown for Long-Term Conditions 169

9.3 Partial Drainage 177

9.4 Shear-Induced Pore Pressure Changes 177

Chapter 10 Seismic Slope Stability 179

10.1 Analysis Procedures 179

10.2 Pseudostatic Screening Analyses 182

10.3 Determining Peak Accelerations 184

10.4 Shear Strength for Pseudostatic Analyses 184

10.5 Postearthquake Stability Analyses 188

Chapter 11 Analyses of Embankments with Partial Consolidation of Weak Foundations 193

11.1 Consolidation During Construction 193

11.2 Analyses of Stability with Partial Consolidation 194

11.3 Observed Behavior of an Embankment Constructed in Stages 195

11.4 Discussion 197

Chapter 12 Analyses to Back-Calculate Strengths 201

12.1 Back-Calculating Average Shear Strength 201

12.2 Back-Calculating Shear Strength Parameters Based on Slip Surface Geometry 203

12.3 Examples of Back-Analyses of Failed Slopes 205

12.4 Practical Problems and Limitation of Back-Analyses 213

12.5 Other Uncertainties 214

Chapter 13 Factors of Safety and Reliability 215

13.1 Definitions of Factor of Safety 215

13.2 Factor of Safety Criteria 216

13.3 Reliability and Probability of Failure 217

13.4 Standard Deviations and Coefficients of Variation 217

13.5 Estimating Reliability and Probability of Failure 220

Chapter 14 Important Details of Stability Analyses 227

14.1 Location of Critical Slip Surfaces 227

14.2 Examination of Noncritical Slip Surfaces 233

14.3 Tension in the Active Zone 234

14.4 Inappropriate Forces in the Passive Zone 238

14.5 Other Details 241

14.6 Verification of Calculations 245

14.7 Three-Dimensional Effects 246

Chapter 15 Presenting Results of Stability Evaluations 249

15.1 Site Characterization and Representation 249

15.2 Soil Property Evaluation 249

15.3 Pore Water Pressures 250

15.4 Special Features 250

15.5 Calculation Procedure 250

15.6 Analysis Summary Figure 250

15.7 Parametric Studies 254

15.8 Detailed Input Data 257

15.9 Table of Contents 257

Chapter 16 Slope Stabilization and Repair 259

16.1 Use of Back-Analysis 259

16.2 Factors Governing Selection of Method of Stabilization 259

16.3 Drainage 260

16.4 Excavations and Buttress Fills 263

16.5 Retaining Structures 264

16.6 Reinforcing Piles and Drilled Shafts 267

16.7 Injection Methods 269

16.8 Vegetation 269

16.9 Thermal Treatment 270

16.10 Bridging 270

16.11 Removal and Replacement of the Sliding Mass 271

Appendix A Slope Stability Charts 273

Appendix B Curved Shear Strength Envelopes Forfully Softened Shear Strengths and Their Impact on Slope Stability Analyses 289

References 295

Index 309

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