Hydro-mechanical Analysis of Rainfall-Induced Landslides (eBook)

Foreword 5
Preface 6
Contents 8
1 Background 12
1.1 Physical Properties of Unsaturated Infiltration 13
1.1.1 Basic Physical Properties 13
1.1.2 Soil Suction 15
1.1.3 Unsaturated Hydraulic Conductivity 16
1.1.4 Total Head 17
1.1.5 Soil–Water Characteristic Curve 18
1.2 Governing Equation of Water Infiltration 20
1.2.1 Richards’ Equation 21
1.3 Shear Strength and Slope Stability 22
1.3.1 Unsaturated Shear Strength 22
1.3.2 Slope Stability 25
References 27
2 Analytical Solution to 1D Coupled Infiltration and Deformation in Unsaturated Porous Media 30
2.1 Introduction 30
2.2 Effect of Rainfall Pattern 31
2.2.1 Governing Equations for Coupled Seepage and Deformation 32
2.2.1.1 Coupled Governing Equations 32
2.2.1.2 Constitutive Relationships for Soil Solids 33
2.2.2 Analytical Solutions to 1D Coupled Infiltration Problems Before and After Ponding 38
2.2.2.1 Coupled Conditions 39
2.2.2.2 Uncoupled Conditions 40
2.2.3 Examples and Analysis Results 41
2.2.4 Conclusions 47
2.3 Effect of Boundary Condition 47
2.3.1 Coupled Infiltration Equations 47
2.3.2 Solution for Infiltration into Deformable Soils 48
2.3.3 Example 50
2.3.3.1 Influence of Rainfall Intensity 50
2.3.3.2 Effect of the Desaturation Coefficient 52
2.3.3.3 Effect of F 53
2.3.3.4 Effect of the Soil Layer Height 53
2.3.4 Conclusions 54
2.4 Effect of Layered Structure 55
2.4.1 Governing Equations 55
2.4.2 Parametric Study 58
2.4.2.1 Effect of H 58
2.4.2.2 Effect of ks 60
2.4.2.3 Effect of ? 62
2.4.2.4 Effect of Soil Porosity ?sb and ?st 63
2.4.2.5 Effect of qA and qB 65
2.4.2.6 Effect of Air-Entry Value 66
2.4.3 Conclusions 67
Appendix 68
References 69
3 Effects of Gravity and Hysteresis on 1D Unsaturated Infiltration 71
3.1 Introduction 71
3.2 Effect of Gravity 72
3.2.1 Governing Equation 72
3.2.1.1 1D Vertical Infiltration 72
3.2.1.2 1D Horizontal Infiltration 73
3.2.2 Boundary and Initial Conditions 74
3.2.2.1 Bottom Boundary 74
3.2.2.2 Prescribed Flux for Surface Condition or Right Boundary 74
3.2.2.3 Constant Pressure Head for Surface and Right Boundaries 75
3.2.2.4 Initial Conditions 75
3.2.3 The Analytical Solutions for Transient Unsaturated Infiltration 76
3.2.3.1 The Analytical Solution to 1D Horizontal Infiltration 76
3.2.3.2 The Analytical Solution to 1D Vertical Infiltration 77
3.2.4 The Analytical Solution for Steady Unsaturated Infiltration 79
3.2.4.1 Vertical Infiltration 79
3.2.4.2 Horizontal Infiltration 80
3.2.5 Case Study and Analysis 81
3.2.6 Summary 85
3.3 Effect of Hysteresis 86
3.3.1 Brief Review of Hysteretic Soil–Water Characteristic Models 86
3.3.2 Mathematical Formulations for Hysteresis 88
3.3.3 Analytical Solutions Considering Hysteresis 89
3.3.3.1 1D Analytical Solution 90
3.3.3.2 Hysteresis Analysis 94
3.3.4 Analysis Examples 96
3.3.5 Conclusions 100
3.4 Effect of Semi-infinite Region 100
3.4.1 Governing Equation 100
3.4.1.1 Coupled Governing Equations 101
3.4.1.2 Analytical Solutions to 1D Semi-infinite Coupled Transient Infiltration 101
3.4.2 Parametric Study 103
3.4.2.1 Effect of the Dimensionless Rainfall Intensity: q/ks 103
3.4.2.2 Effect of the Desaturation Coefficient: ? 104
3.4.2.3 Effect of the Initial Pore-Water Pressure: ur 105
3.4.3 Conclusions 106
References 106
4 2D Infiltration in Unsaturated Porous Media 109
4.1 Introduction 109
4.2 Analytical Solution to Finite Domain 111
4.2.1 Governing Equation of Coupled Infiltration Problems 112
4.2.2 Formulation of the Initial Value Problem 115
4.2.3 Analytical Solutions to Two-Dimensional Coupled Infiltration 117
4.2.4 Numerical Results 118
4.2.5 Conclusions 121
4.3 Numerical Solution to Water Table Rise 121
4.3.1 Governing Equations for the Hydromechanical Processes Involved in Water Table Change 122
4.3.1.1 Static Equilibrium Equations 122
4.3.1.2 van Genuchten Model 123
4.3.1.3 Seepage Equations 124
4.3.2 Computational Modeling 126
4.3.3 Examples of Water Infiltration 126
4.3.3.1 Example 1 127
4.3.3.2 Example 2 130
4.3.4 Discussion and Conclusions 133
4.3.4.1 Discussion 133
4.3.4.2 Conclusions 134
4.4 Surface Infiltration in Semi-infinite Extent 134
4.4.1 Governing Equations for Coupled Seepage and Deformation in Unsaturated Soils 135
4.4.2 Analytical Solution to the Coupled Infiltration in a Semi-infinite Region 136
4.4.3 Computational Modeling of Water Infiltration in a Semi-infinite Unsaturated Region 138
4.5 Conclusions 145
References 146
5 Physical Simulation of Rainfall Infiltration into Unsaturated Slopes 149
5.1 Introduction 149
5.2 Physical Testing of Rainfall-Induced Loose Deposit Slope Failures 152
5.2.1 Model Design 152
5.2.1.1 Experiment Design 152
5.2.2 Analysis of the Slope Model Experiments 157
5.2.3 Conclusions 166
5.3 Laboratory Simulation of Rainfall-Induced Loess Slope Failure 167
5.3.1 Methods 167
5.3.1.1 Experiment Design 167
5.3.1.2 Experimental Process 170
5.3.2 Results and Analysis 170
5.3.2.1 Slope Hydrology 170
5.3.2.2 Slope Deformation 172
5.3.2.3 Analysis of the Landslide Process 174
5.3.3 Numerical Analysis 175
5.3.4 Conclusions 177
5.4 Model Test for Rainfall-Induced Shallow Landslides in Red-Bed Area 178
5.4.1 Geographic and Geologic Setting 179
5.4.2 Theoretical Modeling of Rainfall-Induced Shallow Landslides 180
5.4.2.1 Modified Green–Ampt Rainfall Infiltration Model 180
5.4.2.2 Theoretical Model for Shallow Landslides 182
5.4.3 Laboratory Model Testing of Rainfall-Induced Landslides 184
5.4.3.1 Model Tests 184
5.4.3.2 Volumetric Water Content, Matric Suction, and Pore-Water Pressure Monitoring 185
5.4.3.3 Deformation and Failure Characteristics of the Landslide 188
5.4.4 Verification of the Infiltration Analysis Model 190
5.4.5 Comparative Analysis of the Shallow Landslide Model 190
5.4.6 Conclusions 191
References 192
6 Slope Stability Analysis Based on Coupled Approach 197
6.1 Introduction 197
6.2 Hydromechanical Process of Soil Slope Under Rainfall 199
6.2.1 Equations Governing Coupled Infiltration and Deformation 200
6.2.2 The Limit Equilibrium Method for Stability of an Infinite Soil Slope 203
6.2.3 Analytical Solutions to Rainfall Infiltration in an Infinite Slope 204
6.2.4 Examples and Results 205
6.2.4.1 Influence of Rainfall Intensity on the Pressure Head Section and Stability of the Slope 206
6.2.4.2 Effect of the Slope Height on the Pressure Head Profile and the Stability of the Slope 208
6.2.4.3 Effect of the Slope Angle on the Pressure Head Profile and the Stability of the Slope 209
6.2.5 Conclusions 211
6.3 Hydromechanical Coupling of Unsaturated Soil Slope Stability Due to Rainfall Patterns 211
6.3.1 Theory 211
6.3.1.1 The Soil–Water Characteristic Curves 211
6.3.1.2 Governing Equation of Coupled Infiltration and Deformation 213
6.3.1.3 Solving the Coupled Governing Equations 214
6.3.2 Numerical Calculation of a Homogeneous Soil Slope 214
6.3.2.1 Model and Parameters 214
6.3.2.2 Influence of the Rainfall Pattern 215
6.3.2.3 Effects of the Coefficient of Permeability 221
6.3.3 Conclusions 224
6.4 Three-Phase Coupling of Soil Slope Under Rainfall 224
6.4.1 The Coupled Model 225
6.4.1.1 van Genuchten Model 225
6.4.1.2 Mass Conservation Equations 226
6.4.2 Equilibrium Equation 228
6.4.3 Analysis of Unsaturated Soil Slope Stability 229
6.4.4 Case Studies 230
6.4.4.1 Boundary and Initial Conditions 231
6.4.4.2 Analysis Considering Soil Anisotropy 232
6.4.4.3 Results Considering Anisotropic Properties 236
6.4.5 Conclusions 238
Appendix 239
References 240