LIQUEFACTION MITIGATION IN SILTY SOILS USING STONE COLUMNS SUPPLEMENTED WITH WICK DRAINS BY THEVACHANDRAN SHENTHAN December 2005 Dissertation submitted to the Faculty of the Graduate School of State University of New York at Buffalo In partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Civil, Structural, and Environmental Engineering UMI Number: 3203927 3203927 2006 UMI Microform Copyright All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, MI 48106-1346 by ProQuest Information and Learning Company. To My Wife Suganya… ii ACKNOWLEDGEMENTS I wish to express my deepest gratitude and sincere thanks to my academic advisor – Dr. S. Thevanayagam, for his invaluable guidance, inspiration, as well as support and continuous encouragement, without which this work would not have been possible. I would also like to thank my dissertation committee members Dr. P.K. Banerjee and Dr. S. Ahmad, professors at University at Buffalo, and my external review committee member Dr. G.R. Martin, professor at University of Southern California, for their continuous guidance and invaluable feedback on my research study. I would also like to thank graduate student J. Liang, who helped a lot in carrying out cyclic triaxial tests, and graduate student W. Jia, who helped me in numerical modeling. Graduate students, T. Kanagalingam and R. Nashed are also thanked for helping me in generating the field and laboratory tests database, and supporting me through out my research. I also need to thank my parents, brother, sisters, my parents in law, sister in law, and brothers in law. When I began to pursue a higher degree here, SUNY at Buffalo, it was they who kept on giving me courage and support. Funding for this research work was provided by FHWA / MCEER Highway Project-094, and the financial support is greatly appreciated. Last, but not least, I would like to thank my wife Suganya and my sons Vasheeigaran and Vagish for their everlasting love, support and encouragement. iii Table of Contents Contents Page Acknowledgements iii Table of Contents iv List of Tables xi List of Figures xiii Notations xvii Abstract xxii Chapter I Introduction 01 1.0 Introduction 01 1.1 Scope of This Study 03 1.2 Organization of Thesis 07 Chapter II Review of Ground Improvement Techniques 09 2.0 Ground Improvement Techniques to Prevent Liquefaction 09 2.1 Densification Methods 12 2.1.1 Vibro Compaction 12 2.1.2 Vibro Replacement Stone Columns 14 iv 2.1.3 Vibro Concrete Columns 19 2.1.4 Deep Dynamic Compaction 19 2.1.5 Deep Blasting 20 2.1.6 Compaction Grouting 23 2.1.7 Displacement Piles 24 2.2 Drainage Methods 24 2.2.1 Gravel Drains 25 2.2.2 Prefabricated Vertical Drains 28 2.3 Reinforcement Methods 29 2.4 Stabilization Methods by Grouting/Admixtures 30 2.4.1 Jet Grouting 31 2.4.2 Permeation (Chemical) Grouting 33 2.4.3 Intrusion Grouting 34 2.4.4 Electro-Kinetic Injection 34 2.4.5 Deep Soil Mixing 35 2.4.6 Compacted Soil-Cement Mix 36 2.5 Review of Design Methods for Stone Columns 37 2.5.1 Densification 38 2.5.2 Drainage 39 2.5.3 Seismic Shear Stress Redistribution 47 v 2.5.4 Limitations 50 2.5.5 Stone Columns with Supplementary Wick Drains 50 2.6 Summary 52 Chapter III Liquefaction Behavior of Soils 53 3.0 Liquefaction Behavior of Sands and Silty Soils 53 3.1 Cyclic Strength 54 3.2 Pore Pressure Generation Behavior 55 3.3 Post-Liquefaction Pore Pressure Dissipation and Densification 55 3.4 Recent Developments in Understanding Liquefaction -Behavior of Silty Soils 57 3.4.1 Grain Contact Density Indices 57 3.4.2 Static Liquefaction 59 Chapter IV Laboratory Experimental Study 60 4.0 Experimental Program 60 4.1 Materials and Apparatus 62 4.2 Test Procedure 67 4.2.1 Specimen Preparation 67 4.2.2 Manual Saturation 68 4.2.3 Initializing the GEOCOMP Apparatus 68 4.2.4 Back Pressure Saturation and Consolidation 68 vi 4.2.5 Cyclic Loading 69 4.2.6 Pore Pressure Dissipation and Volumetric Strain 71 4.2.7 Hydraulic Conductivity 71 4.2.8 Data Acquisition and Interpretation 72 4.3 Experimental Errors 73 4.3.1 Accuracy of Measuring Devices 73 4.3.2 Membrane Compliance 74 Chapter V Analysis of Experimental Results 75 5.0 Introduction 75 5.1 Pore Pressure Generation 76 5.2 Compressibility 80 5.3 Coefficient of Consolidation 83 5.4 Post-Liquefaction Densification 89 5.5 Cyclic Strength 94 5.6 Energy Based Approach to Cyclic Resistance 97 5.7 Conclusion 98 Chapter VI Numerical Modeling 99 6.0 Introduction 99 6.1 Stone Column Installation Process 101 6.2 Theoretical Framework 103 vii 6.2.1 Pore Pressure Generation 103 6.2.2 Pore Pressure Dissipation 118 6.2.3 Densification 119 6.3 Numerical Simulation of Stone Column Installation Process 119 6.3.1 Formulation of the Finite Difference Numerical Scheme 120 6.3.2 Simplification of the Problem and Boundary Conditions 121 6.3.3 Parametric Study: Stone Columns in Sands & Silts 124 6.3.4 Parametric Study: Composite Stone Columns in Sands and Silts 129 6.3.5 Effect of Cavity Expansion 138 6.4 Performance of Stone Columns During an Earthquake 141 6.5 Stone Column Installation – Quality Control 142 6.6 Summary 146 Chapter VII Field Study – Stone Column Installation 148 7.0 Introduction 148 7.1 Soil Conditions 148 7.2 Liquefaction and Settlement Analyses 150 7.3 Recommendations 151 viii 7.4 Equipment and Basic Construction Procedure 153 7.5 Instrumentation 154 7.6 Observations 159 7.7 Verification of Numerical Simulations 166 Chapter VIII Design Charts and Design Guidelines 170 8.0 Introduction 170 8.1 Assumptions 170 8.2 Design Charts 172 8.3 Design Guidelines 175 8.4 Sample Design 178 Chapter IX Conclusions and Recommendations 182 9.0 Conclusions 182 9.1 Recommendations 185 References 187 Appendix: A- Sample Interpretation 202 B- Test Results Summary Table 208 C- Individual Test Summary and Interpretation 212 D- Field Test Data 293 ix [...]... show stone columns supplemented with wick drains work well in such soils This study focuses on three aspects: (i) examining the reasons for the sub-performance of stone columns in silty soils, identifying key soil parameters that hinder the effectiveness of stone columns, and developing means to improve the effectiveness of this method in silty soils including provision of supplementary wick drains, ... developing a numerical model to simulate stone column installation with and without wick drains, and qualitatively evaluate the degree of ground improvement, and (iii) verifying the numerical simulation results using case histories and field experimental studies, and developing modified design charts and guidelines for designing stone columns with and without wick drains to improve sands and silty soils. .. and silty soils with varying initial conditions improved using stone columns with and without wick drains The model was fine tuned and tested using case studies and field measurements Design charts and design guidelines that were developed based on the extensive experimental and numerical study are presented Recommendations for improving the stone column design methodology, and for further research in. .. dependent on grain size characteristics Low coefficient of consolidation associated with silty soils precludes faster pore pressure dissipation during stone column installation and therefore hinders densification around the stone columns during installation It also hinders drainage during earthquakes This appears to be the primary reason for the lack of effectiveness of stone columns in silty soils Numerical... stone columns are in use to mitigate liquefaction hazards in sandy soils for almost three decades There are three mechanisms that help reduce liquefaction potential of a sandy soil improved using stone columns During stone column installation sandy soils densify due to installation vibration Further, the stiffness of the composite improved soil increases leading to a reduction in cyclic shear stress induced... soil surrounding the stone columns during earthquakes In addition, pore pressures generated in the soil during earthquakes are quickly dissipated through the highly permeable stone columns These combined mechanisms reduce the liquefaction potential of the improved soil Sandy soil sites improved using stone columns have performed well during earthquakes However, its effectiveness in silty soils is limited... available for composite stone columns (vibro stone columns supplemented with wick drains) installed in silty soil sites Therefore, a field study was conducted at a silty soil site, Marina del Rey, Los Angeles County, CA These field observations were used to refine the numerical model Using the new numerical simulation program composite stone column design charts were developed Design guidelines and sample... for liquefaction mitigation and a detailed review of current design methods for liquefaction mitigation using stone columns It also presents a brief summary of case histories of liquefaction mitigation and identifies the applicability and limitations of the various methods for liquefaction mitigation in silty soils Chapter three presents a review of recent understanding of liquefaction behavior of silty. .. numerical model was developed to simulate vibro stone column (with or without pre-installed wick drains) installation process This model also capable of analyzing pore pressure changes within the improved soil in the event of an earthquake Several simulations were done to compare its results with those reported in the literature for clean sands with vibro stone columns alone, and found to be on good agreement... compaction Vibro compaction Densification Vibro replacement stone columns; Deep blasting Compaction grouting Drainage Reinforcement Gravel drains Prefabricated drains Steel and precast concrete piles Sheet piles Permeation grouting Cementation/Solidification by Grouting Jet grouting Deep soil mixing Lime/cement injection 2 Densification technique using dynamic compaction requires open ground conditions . LIQUEFACTION MITIGATION IN SILTY SOILS USING STONE COLUMNS SUPPLEMENTED WITH WICK DRAINS BY THEVACHANDRAN SHENTHAN December 2005. for Stone Columns 37 2.5.1 Densification 38 2.5.2 Drainage 39 2.5.3 Seismic Shear Stress Redistribution 47 v 2.5.4 Limitations 50 2.5.5 Stone Columns with Supplementary Wick Drains. Stone Columns in Sands & Silts 124 6.3.4 Parametric Study: Composite Stone Columns in Sands and Silts 129 6.3.5 Effect of Cavity Expansion 138 6.4 Performance of Stone Columns During