Deformation and Failure Mechanism of Excavation in Clay Subjected to Hydraulic Uplift (Advanced Topics in Science and Technology in China)

"This book presents the latest experimental and numerical analysis work in the field of ground deformation and base instability of deep excavations in soft clay subjected to hydraulic uplift. The authors? latest research findings, based on dimensional analyses, well-instrumented full-scale field tests, systematic coupled-consolidation finite element analyses and centrifuge tests are reported. This book shows how to systematically approach a complex geotechnical problem, from identifying existing problems, reviewing literature, to dimensional and numerical analyses, validation through full-scale testing and centrifuge model testing. The methodologies are also introduced as major tools adopted in geotechnical research"--OhioLink Library Catalog Preface 6 Contents 8 Nomenclature 13 1 Introduction 15 1.1 Background 15 1.2 Objectives 16 1.3 Book Outline 17 References 17 2 Literature Review 19 2.1 Introduction 19 2.2 Ground Deformation Due to Excavation 19 2.2.1 Field Investigation 19 2.2.2 Numerical Analysis 22 2.2.3 Analytical Solution 24 2.2.4 Centrifuge Modelling 25 2.3 Soil-Structure Interaction of Multi-propped Excavation 26 2.3.1 Field Investigation 26 2.3.2 Numerical Analysis 27 2.3.3 Centrifuge Modelling 28 2.4 Excavation Base Instability Due to Hydraulic Uplift 29 2.4.1 Field Investigation 29 2.4.2 Recommendations in Design Codes 31 2.5 Techniques for Simulation of Multi-propped Excavation in Centrifuge 31 2.6 Summary 32 References 33 3 Field Investigation of a Multi-propped Excavation in Soft Clay 35 3.1 Introduction 35 3.2 The Site 36 3.2.1 Geotechnical Profile 36 3.2.2 Construction Sequence 39 3.3 Instrumentation 42 3.4 Ground Deformation and Soil-Structure Interaction at Panel 4 44 3.4.1 Lateral Wall Displacement of Panel 4 44 3.4.2 Lateral Ground Movement Behind Panel 4 45 3.4.3 Ground Surface Settlement Behind Panel 4 45 3.4.4 Ground Surface Settlement and delta v-Max/ delta h-Max Ratios in Shanghai 46 3.4.5 Change of Lateral Total Earth Pressure 48 3.4.6 Distrubtion of Lateral Total Earth Pressure 49 3.4.7 Prop Load and Equilibrium Analysis of Wall 51 3.4.8 Apparent Pressure Envelope for Excavations in Shanghai 52 3.4.9 Pore Water Pressure 54 3.4.10 Effective Stress Path 55 3.5 Summary and Conclusions 57 References 58 4 Numerical Analyses of the Multi-propped Excavation in Soft Clay 60 4.1 Background 60 4.2 Finite Element Analysis 61 4.2.1 Finite Element Mesh and Boundary Conditions 61 4.2.2 Constitutive Model and Model Parameters 62 4.2.3 Numerical Modelling Procedure 63 4.3 Comparison of Measured and Computed Results 63 4.3.1 Lateral Wall Displacement 63 4.3.2 Ground Surface Settlement 66 4.3.3 Contour of Deviatoric Strain 68 4.3.4 Mobilisation of Undrained Shear Strength 69 4.3.5 Lateral Total Earth Pressure 70 4.3.6 Pore Water Pressure 72 4.3.7 Apparent Earth Pressure 73 4.4 Summary and Conclusions 74 References 75 5 Dimensional Analysis of Excavation in Clay Subjected Hydraulic Uplift 77 5.1 Introduction 77 5.2 Variables Affecting Basal Resistance Against Hydraulic Uplift 77 5.3 Dimensional Analysis 78 5.4 Key Dimensionless Groups for This Study 79 References 80 6 Centrifuge Modelling of Multi-propped Excavation in Clay Destabilised by Hydraulic Uplift 82 6.1 Introduction 82 6.2 Principles and Scaling Laws 82 6.3 Limitations of Centrifuge Modelling 84 6.3.1 Variation of Centrifugal Acceleration with Model Depth 84 6.3.2 Grain Size Effect 85 6.3.3 Boundary Effect 85 6.4 Test Program and Objectives 86 6.5 Model Package 86 6.5.1 Actuator: For Simulating Prop Installation 87 6.5.2 Rubber Bag: For Simulating Excavation 89 6.5.3 Flow Rate Control Valve: Controlling Excavation Rate 90 6.5.4 Model Wall 90 6.5.5 Model Prop 91 6.5.6 Model Pile 91 6.6 Model Preparation and Characterisation of Undrained Shear Strength of Clay 92 6.7 Instrumentation 97 6.7.1 Measurement of Pore Water Pressure 98 6.7.2 Measurement of Ground Settlement 99 6.7.3 Measurement of Undrained Shear Strength of Clay 100 6.7.4 Measurement of Prop Load 101 6.7.5 Measurement of Bending Movement and Axial Load of Pile 101 6.7.6 Measurement of Subsurface Soil Movement 102 6.8 Test Procedure 104 References 105 7 Finite Element Analyses: For Back-Analysis and Parametric Study 107 7.1 Introduction 107 7.2 Back-Analyses of Centrifuge Tests 108 7.2.1 Finite Element Mesh and Boundary Conditions 108 7.2.2 Constitutive Model and Model Parameters 109 7.2.3 Numerical Modelling Procedure 110 7.3 Numerical Parametric Study 110 References 111 8 Interpretations of Measured and Back-Anlaysed Results of Centrifuge Tests 112 8.1 Introduction 112 8.2 Interpretation of Measured and Computed Results 112 8.2.1 Profiles of Over-Consolidation Ratio and At-Rest Lateral Earth Pressure Coefficient 112 8.2.2 Undrained Shear Strength Profile 113 8.2.3 Lateral Wall Displacement 115 8.2.4 Ground Deformation Mechanism Due to Excavation 116 8.2.5 Ground Deformation Mechanism Due to Hydraulic Uplift 119 8.2.6 Uplift Movement in Response to Hydraulic Uplift 121 8.2.7 Bending Moment and Axial Load in Piles 122 8.2.8 Prop Load 124 8.3 Improved Understanding from Numerical Back-Analysis 125 8.3.1 Comparison Between ``Idealised Modelling Technique'' and ``Rigorous Modelling Technique'' 125 8.3.2 Mobilised Undrained Shear Strength 126 8.3.3 Load Transfer from Soil to Pile 128 8.4 Numerical Parametric Study on Embedment Depth of Piles 130 8.4.1 Influence of Pile Length on Effectiveness of Base Stabilisation 130 8.4.2 Axial Load and Unit Shaft Friction of Piles with Varied Lengths 131 8.5 Summary and Conclusions 132 References 133 9 Numerical Parametric Study 135 9.1 Introduction 135 9.2 Numerical Parametric Study 135 9.3 Results of Numerical Parametric Study 137 9.3.1 Uplift Movement in Response of Hydraulic Pressure 137 9.3.2 Initiation of Hydraulic Uplift 138 9.3.3 Calculation Chart for Estimating Initiation of Hydraulic Uplift (Pi) 139 9.3.4 Failure Mechanism 140 9.3.5 Change of Pore Water Pressure in Response to Hydraulic Uplift 144 9.3.6 Change of Effective Stress Path in Response to Hydraulic Uplift 146 9.4 An Alternative Method for Base Stabilisation 147 9.5 Summary and Conclusions 149 References 150 10 Conclusions and Future Work 152 10.1 Summary of This Research 152 10.2 Ground Deformation of Multi-propped Excavation in Soft Clay 153 10.2.1 Comparison Between Excavation in Greenfield Site and Densely Built Area 153 10.2.2 Influence Factors on Ground Deformation of Excavations in Shanghai 154 10.3 Soil-Structure Interaction of Multi-propped Excavation in Soft Clay 155 10.3.1 Lateral Total Earth Pressure 155 10.3.2 Pore Water Pressure 155 10.3.3 Effective Stress Path 156 10.3.4 Effect of Jet Grouted Prop on Soil-Structure Interaction 156 10.3.5 Prop Load 157 10.4 Excavation Base Instability Associated with Hydraulic Uplift 157 10.4.1 Initiation of Base Instability 157 10.4.2 Failure Mechanisms 158 10.4.3 Proposed Alternative Methods for Base Stabilisation 158 10.4.4 Verification of `Idealised Modelling Technique' 158 10.5 Recommendations for Further Work 159 10.5.1 Further Verification of `Greenfield Effect' 159 10.5.2 Further Verification of `Idealised Modelling Technique' 159 10.5.3 Alternative Methods for Base Stabilisation 159 References 160 Index 161 Front Matter....Pages i-xiv Introduction....Pages 1-4 Literature Review....Pages 5-20 Field Investigation of a Multi-propped Excavation in Soft Clay....Pages 21-45 Numerical Analyses of the Multi-propped Excavation in Soft Clay....Pages 47-63 Dimensional Analysis of Excavation in Clay Subjected Hydraulic Uplift....Pages 65-69 Centrifuge Modelling of Multi-propped Excavation in Clay Destabilised by Hydraulic Uplift ....Pages 71-95 Finite Element Analyses: For Back-Analysis and Parametric Study....Pages 97-101 Interpretations of Measured and Back-Anlaysed Results of Centrifuge Tests....Pages 103-125 Numerical Parametric Study....Pages 127-143 Conclusions and Future Work....Pages 145-153 Back Matter....Pages 155-156