Soil Strength and Slope Stability

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 MaterialsSand, 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 Reli