1 Background 1.1 Physical Properties of Unsaturated Infiltration 1.1.1 Basic Physical Properties 1.1.2 Soil Suction 1.1.3 Unsaturated Hydraulic Conductivity 1.1.4 Total Head 1.1.5 Soil-Water Characteristic Curve 1.2 Governing Equation of Water Infiltration 1.2.1 Richards' Equation 1.3 Shear Strength and Slope Stability 1.3.1 Unsaturated Shear Strength 1.3.2 Slope Stability References 2 Analytical Solution to 1D Coupled Infiltration and Deformation in Unsaturated Porous Media 2.1 Introduction 2.2 Effect of Rainfall Pattern 2.2.1 Governing Equations for Coupled Seepage and Deformation 2.2.2 Analytical Solutions to 1D Coupled Infiltration Problems Before and After Ponding 2.2.3 Examples and Analysis Results 2.2.4 Conclusions 2.3 Effect of Boundary Condition 2.3.1 Coupled Infiltration Equations 2.3.2 Solution for Infiltration into Deformable Soils 2.3.3 Example 2.3.4 Conclusions 2.4 Effect of Layered Structure 2.4.1 Governing Equations 2.4.2 Parametric Study 2.4.3 Conclusions Appendix References 3 Effects of Gravity and Hysteresis on 1D Unsaturated Infiltration 3.1 Introduction 3.2 Effect of Gravity 3.2.1 Governing Equation 3.2.2 Boundary and Initial Conditions 3.2.3 The Analytical Solutions for Transient Unsaturated Infiltration 3.2.4 The Analytical Solution for Steady Unsaturated Infiltration 3.2.5 Case Study and Analysis 3.2.6 Summary 3.3 Effect of Hysteresis 3.3.1 Brief Review of Hysteretic Soil-Water Characteristic Models 3.3.2 Mathematical Formulations for Hysteresis 3.3.3 Analytical Solutions Considering Hysteresis 3.3.4 Analysis Examples 3.3.5 Conclusions 3.4 Effect of Semi-infinite Region 3.4.1 Governing Equation 3.4.2 Parametric Study 3.4.3 Conclusions References 4 2D Infiltration in Unsaturated Porous Media 4.1 Introduction 4.2 Analytical Solution to Finite Domain 4.2.1 Governing Equation of Coupled Infiltration Problems 4.2.2 Formulation of the Initial Value Problem 4.2.3 Analytical Solutions to Two-Dimensional Coupled Infiltration 4.2.4 Numerical Results 4.2.5 Conclusions 4.3 Numerical Solution to Water Table Rise 4.3.1 Governing Equations for the Hydromechanical Processes Involved in Water Table Change 4.3.2 Computational Modeling 4.3.3 Examples of Water Infiltration 4.3.4 Discussion and Conclusions 4.4 Surface Infiltration in Semi-infinite Extent 4.4.1 Governing Equations for Coupled Seepage and Deformation in Unsaturated Soils 4.4.2 Analytical Solution to the Coupled Infiltration in a Semi-infinite Region 4.4.3 Computational Modeling of Water Infiltration in a Semi-infinite Unsaturated Region 4.5 Conclusions References 5 Physical Simulation of Rainfall Infiltration into Unsaturated Slopes 5.1 Introduction 5.2 Physical Testing of Rainfall-Induced Loose Deposit Slope Failures 5.2.1 Model Design 5.2.2 Analysis of the Slope Model Experiments 5.2.3 Conclusions 5.3 Laboratory Simulation of Rainfall-Induced Loess Slope Failure 5.3.1 Methods 5.3.2 Results and Analysis 5.3.3 Numerical Analysis 5.3.4 Conclusions 5.4 Model Test for Rainfall-Induced Shallow Landslides in Red-Bed Area 5.4.1 Geographic and Geologic Setting 5.4.2 Theoretical Modeling of Rainfall-Induced Shallow Landslides 5.4.3 Laboratory Model Testing of Rainfall-Induced Landslides 5.4.4 Verification of the Infiltration Analysis Model 5.4.5 Comparative Analysis of the Shallow Landslide Model 5.4.6 Conclusions References 6 Slope Stability Analysis Based on Coupled Approach 6.1 Introduction 6.2 Hydromechanical Process of Soil Slope Under Rainfall 6.2.1 Equations Governing Coupled Infiltration and Deformation 6.2.2 The Limit Equilibrium Method for Stability of an Infinite Soil Slope 6.2.3 Analytical Solutions to Rainfall Infiltration in an Infinite Slope 6.2.4 Examples and Results 6.2.5 Conclusions 6.3 Hydromechanical Coupling of Unsaturated Soil Slope Stability Due to Rainfall Patterns 6.3.1 Theory 6.3.2 Numerical Calculation of a Homogeneous Soil Slope 6.3.3 Conclusions 6.4 Three-Phase Coupling of Soil Slope Under Rainfall 6.4.1 The Coupled Model 6.4.2 Equilibrium Equation 6.4.3 Analysis of Unsaturated Soil Slope Stability 6.4.4 Case Studies 6.4.5 Conclusions Appendix References