This book focuses on the engineering properties of unsaturated widely graded soils and their influence on slope stability. This book characterizes the natural widely graded colluvial soils from macroscale, mesoscale, and microscale viewpoints, introduces the techniques for measuring hydro-mechanical properties for unsaturated widely graded colluvial soils, and clarifies the hydro-mechanical behavior and the failure mechanism of widely graded colluvial soils subjected to environmental loads. This book improves the understanding of rainfall-induced landslides on natural slopes. Researchers and engineers in the field of civil engineering can benefit from the book.
Author(s): Xu Li, Hongfen Zhao, Limin Zhang
Publisher: Springer
Year: 2022
Language: English
Pages: 407
City: Singapore
Foreword
Preface
Acknowledgments
Contents
1 Introduction
1.1 Background
1.2 Fundamental Behavior for Assessing the Stability of Widely-Graded Soil Deposits
1.2.1 Mechanism of the Trigging of Widely-Graded Soil Landslides
1.2.2 Fundamental Behavior for Assessing the Infiltration Process of Widely-Graded Soil Deposits
1.2.3 Fundamental Behavior for Assessing the Instability Process of Widely-Graded Soil Deposits
1.3 Outline of This Book
References
2 Particle-Size Distribution and Density of Natural Widely-Graded Colluvial Soils
2.1 Introduction
2.2 Properties of Natural Colluvial Soils
2.2.1 Segregation of Soil Particles During a Landslide
2.2.2 Particle Flow and Segregation in a Landslide Triggered by Wenchuan Earthquake
2.2.3 Grain-Size Distribution Analysis of Natural Colluvial Soil
2.3 Soil Samples for Representing In-Situ Soil Behavior
2.3.1 Grain-Size Distribution Design of Artificial Soils for Laboratory Experiments
2.3.2 Soil Density Design
2.4 Soil Specimen Preparation
2.5 Basic Soil Properties
2.6 Summary
References
3 Microporosity Structures of Widely-Graded Soils
3.1 Introduction
3.2 Experimental Techniques
3.3 Mathematical Description of Dual-Porosity Geometry
3.4 Comprehensive Study of Microporosity for LC with Sand
3.4.1 Experimental Technique
3.4.2 Dual-Porosity Structure of Compacted Soil
3.4.3 Dual-Porosity Structure Change Due to Soil Compaction
3.4.4 Dual-Porosity Structure Evolution During Soil Saturation
3.4.5 Dual-Porosity Structure Changes During Drying
3.5 Investigation of Microporosity Structure for Coarse Soils
3.5.1 Experimental Program
3.5.2 Estimation of Volume of Pores with Radii Out of Measurement Range
3.5.3 Evolution of Dual-Porosity Structure Upon Wetting
3.5.4 Micropore Shrinkage After Drying
3.5.5 Effect of the Coarse Fraction on Soil Porosity Structure
3.6 Summary
References
4 Techniques for Measuring Hydraulic Properties for Unsaturated Soils
4.1 Introduction
4.2 Development of a SWCC Device for Testing Gravelly Soils at Very Low Suctions
4.2.1 Difficulties in Measuring SWCC of Gravel Soils at Very Low Suctions
4.2.2 A New SWCC Device for Using at Very Low Suctions
4.2.3 Experimental Procedure
4.2.4 Error Evaluation
4.2.5 Data Interpretation Procedure
4.3 Development of a Device for Measuring SHCF Using Wetting Front Advancing Column Tests
4.3.1 A Large-Scale Column Device for Measuring SHCF
4.3.2 Experimental Procedure and Boundary Conditions
4.3.3 Interpretation of SHCF Based on the WFAM
4.3.4 Limitations of the Application of WFAM
4.4 Measuring SHCF Over a Wide Suction Range
4.4.1 Combining WFAM and IPM for the Measurement of Hydraulic Conductivity
4.4.2 Numerical Tests
4.4.3 Validation of the Digital WFAM
4.4.4 Comparison of WFAM and the Traditional IPM
4.4.5 Error Analysis for WFAM and IPM
4.4.6 A Combined IPM and WFAM for Measuring SHCF in Full Suction Range
4.4.7 Limitations of This Study
4.5 Summary
References
5 Unsaturated Hydraulic Properties for Widely-Graded Soils
5.1 Introduction
5.2 Properties of SWCCs for Widely-Graded Soils
5.2.1 Other Experimental Techniques for Measuring SWCCs
5.2.2 Effect of Coarse Fractions on SWCC
5.2.3 Influence of Soil Density on SWCC
5.2.4 Influence of Sample Size on SWCC
5.2.5 Hysteresis in SWCCs
5.3 SHCFs for Widely-Graded Soils
5.3.1 Saturated Soil Hydraulic Conductivity Measurement
5.3.2 Infiltration Process in Column Tests of Colluvial Soils
5.3.3 Calculated Unsaturated SHCFs
5.4 Summary
References
6 A Unified Framework for Unsaturated Hydraulic Behavior of Widely-Graded Soils
6.1 Introduction
6.2 Experimental Data
6.3 Fabric—A State-Dependent Variable of Soil
6.3.1 Definition of Pore-Size Distribution
6.3.2 Fabric Variation upon Mechanical Actions
6.3.3 Fabric Variation upon Water Actions
6.4 Drying Process in Void Ratio-Water Content and Void Ratio–Suction Domain
6.4.1 Definition of Soil Shrinkage Curve
6.4.2 Shrinkage Curve of Sample Drying from a Slurry State or Slightly Compacted State
6.4.3 Shrinkage Curve of Overconsolidated or Compacted Sample
6.5 Drying Process in Water Content—Suction Domain
6.5.1 Definition of Soil Water Characteristic Curve
6.5.2 Soil Water Characteristic Curve Affected by Soil Consolidation or Compaction
6.6 Drying Process in Void Ratio—Water Content—Suction Domain
6.7 Drying Process in Water Content—Fabric Domain and Void Ratio—Fabric Domain
6.7.1 Water Retention Ability Controlled by PSD
6.7.2 Drying Process in Void Ratio—Fabric Domain
6.7.3 Drying Process in Water Content—Fabric Domain
6.8 Case Study: SWCC and SC Prediction Based on Variable PSDs
6.9 Summary
References
7 Shearing Behavior of Widely-Graded Soils Under Low Confining Pressures
7.1 Introduction
7.2 Experimental Techniques
7.2.1 Experimental Apparatuses
7.2.2 Experimental Program and Stress Paths
7.2.3 Preparation of Soil Specimens
7.2.4 Test Procedures
7.3 Shearing Behavior of Saturated Widely-Graded Soils
7.3.1 Effect of Coarse Fraction on Compressibility
7.3.2 Effect of Coarse Content on Shearing Behavior
7.3.3 Effect of Coarse Content on Critical Friction Angle
7.3.4 Implication to Engineering Practice
7.4 Shearing Behavior of Unsaturated Widely-Graded Soils
7.4.1 Drained Shearing Behavior of Unsaturated Soils
7.4.2 Variation of Peak Shear Strength of Unsaturated Soils with Coarse Content
7.4.3 Variation of the Critical-State Strength of Unsaturated Soils with Coarse Content
7.5 Summary
References
8 Bimodal Features for Widely-Graded Soils
8.1 Introduction
8.2 Bimodal Pore Structure of Coarse Widely-Graded Soil
8.2.1 Pore-Size Distribution and Soil Fabric
8.3 Bimodal SWCC
8.3.1 Features of a Bimodal Soil–Water Characteristic Curve
8.3.2 Physical Model for the Bimodal Soil–Water Characteristic Curve
8.3.3 New Bimodal SWCC Model
8.3.4 SWCC Prediction Based on Grain-Size Distribution
8.3.5 SWCC Prediction Based on Pore-Size Distribution
8.4 Bimodal SHCFs
8.4.1 Link Between SHCF and SWCC
8.4.2 Bimodal SHCF
8.4.3 Fitting of Bimodal SHCFs
8.4.4 Estimation of Parameters Involved in Bimodal SHCFs
8.5 Bimodal Shear Strength
8.5.1 Variation of Compressibility with Suction
8.5.2 Variation of Shear Strength with Suction
8.5.3 Evaluation of Various Shear Strength Equations for Unsaturated Soils
8.5.4 Proposed Shear Strength Equations for Granular Soils with Bimodal SWCCs
8.5.5 Comparison Between Experimental and Predicted Results
8.6 Summary
References
9 Convergence Criterion for Highly Nonlinear Unsaturated Seepage Analysis
9.1 Introduction
9.2 Numerical Problems Caused by Mesh Size and Time Step in Unsaturated Seepage Analysis
9.2.1 Highly Nonlinear Properties of Unsaturated Soils
9.2.2 Mesh Size-Dependent Problem in the Simulation of Unsaturated Seepage
9.2.3 Time Step-Dependent Problem in the Simulation of Unsaturated Seepage Analysis
9.2.4 Effect of Solving Method
9.2.5 Summary
9.3 Theoretical Analysis on the Accuracy of Numerical Simulation of Unsaturated Seepage
9.3.1 Definition of Critical Mesh Size and Time Step
9.3.2 Critical Mesh Size in the Finite-Difference Method
9.3.3 Critical Time Step in the Finite-Difference Method
9.4 Numerical Test Plan and Test Procedure
9.4.1 Numerical Model of Nonlinear Unsaturated Seepage Process
9.4.2 Numerical Test Plan
9.4.3 Procedure of Determining Lc and Δtc
9.5 Numerical Study on the Convergence Criterion of Critical Mesh Size Lc
9.5.1 Numerical Test Results of Lc Values
9.5.2 A Semi-empirical and Semi-theoretical Criterion for Lc
9.5.3 Verification of Lc Criterion
9.6 Numerical Study on the Convergence Criterion of Time Step Δtc
9.6.1 Numerical Test Results of Δtc Values
9.6.2 A Semi-empirical and Semi-theoretical Criterion for Δtc
9.6.3 Verification of Δtc Criterion
9.7 Application of the Proposed Convergence Criterion of Lc and Δtc
9.7.1 1D Analytical Solution
9.7.2 2D Model Test
9.7.3 2D Engineering Problem
9.8 Selection of Mesh Size and Time Step in Unsaturated Seepage Simulation
9.8.1 Recommended Values in Various Seepage Conditions
9.8.2 Discussion
9.9 Conclusions
Appendix
Application of Proposed Criteria in Infiltration Boundaries
References
10 Assessing the Stability of Widely-Graded Soils
10.1 Introduction
10.2 Instability of Saturated and Unsaturated Coarse Granular Soils
10.2.1 Experimental Program
10.2.2 Instability in the Microstructures of the Granular Soils
10.2.3 Instability of Saturated Granular Soils During Shearing
10.3 Case Study 1: Hydraulic Behavior of Colluvial Slopes upon a Rainstorm
10.3.1 Simulation Methodology
10.3.2 Seepage Analysis Results
10.3.3 Stability Analysis Results
10.4 Case Study 2: Identification of Hazardous Loose Landslide Deposits and Scars Formed During the 2008 Wenchuan Earthquake
10.4.1 Introduction
10.4.2 Geographic and Geological Settings Near K34
10.4.3 Inventory of Failures Occurred in 2009–2010
10.4.4 Identification of Sources of Risk at K34
10.4.5 Reliability Analysis
10.5 Summary
References
