LIQUEFACTION ANALYSIS OF LEVEL AND SLOPING GROUND USING FIELD CASE HISTORIES AND PENETRATION RESISTANCE BY SCOTT MICHAEL OLSON B.S., University of Illinois at Urbana-Champaign, 1994 M.S., University of Illinois at Urbana-Champaign, 1995 THESIS Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering in the Graduate College of the University of Illinois at Urbana-Champaign, 2001 Urbana, Illinois ABSTRACT The primary objective of this study was to develop simple, empirical tools to evaluate liquefaction problems in level and sloping ground. The proposed correlations and procedures are particularly useful as screening tools because of their simplicity. Specifically, these procedures include: 1. CPT-based level ground liquefaction resistance relationships for sandy soils; 2. SPT- and CPT-based relationships to estimate the yield shear strength available at the triggering of liquefaction in ground subjected to a static shear stress; 3. SPT- and CPT-based relationships to estimate the liquefied shear strength available at large deformation after the triggering of liquefaction in ground subjected to a static shear stress; and 4. A comprehensive liquefaction analysis procedure for ground subjected to a static shear stress that addresses liquefaction susceptibility, triggering of liquefaction, and post-triggering stability. The author collected a database of 172 level ground liquefaction and non- liquefaction case histories where CPT results are available. These cases were separated into those involving clean sands (less than 5% fines content), silty sands (between 5 and 35% fines content), and silty sands to sandy silts (greater than 35% fines content) to develop three separate liquefaction resistance relationships based on fines content (percentage by weight passing the U.S. Standard #200 sieve). The proposed relationships also use median grain size (D ) to classify the case histories. 50 i The author collected thirty-three case histories of liquefaction flow failure where SPT and/or CPT results are available or can be reasonably estimated. These flow failure case histories were back-analyzed to evaluate the yield shear strength and yield strength ratio mobilized at the triggering of liquefaction. Relationships between yield strength ratio and corrected SPT and CPT resistance were developed for use in liquefaction triggering analysis. The flow failure case histories also were back-analyzed to evaluate the liquefied shear strength and liquefied strength ratio mobilized at large deformation. For cases with sufficient information, the stability back-analysis incorporated the kinetics of failure (i.e., momentum). Relationships between liquefied strength ratio and corrected SPT and CPT resistance were developed for use in post-triggering stability analysis. Lastly, the author proposes a comprehensive liquefaction analysis procedure for sandy soils to evaluate: (1) liquefaction susceptibility; (2) triggering of liquefaction; and (3) post-triggering/flow failure stability. The procedure incorporates the proposed relationships to estimate yield strength ratio and liquefied strength ratio, and does not require a suite of laboratory tests or corrections for sloping ground and vertical effective stress. The procedure is verified initially using the Lower San Fernando Dam case history, and is particularly useful as a screening tool. ii ACKNOWLEDGMENTS I would like to express my gratitude to everyone who has contributed to this study. Special thanks are extended to: Dr. Timothy D. Stark, my Advisor, for his support and encouragement, and for introducing me to the challenging and rewarding profession of geotechnical engineering; Drs. Gholamreza Mesri, James H. Long, Youssef Hashash, and Mr. Peter A. Lenzini for their constructive criticism and encouragement; Drs. David E. Daniel and Edward J. Cording for their valuable advice; Mrs. Myrna Webber for her tireless support, help, and friendship; Dr. Stephen F. Obermeier for his valuable advice and friendship; Dr. Marawan Shahien for his constant willingness to discuss technical and non-technical issues; my parents, Kenneth J. and Janet L. Olson, for their enduring support and encouragement throughout my undergraduate and graduate years; Katrina, my wife, partner, and best friend, for her never-ending love and strength – thank you for never letting me lose focus; and my daughter, Hailey, who was too young to remember Dad trying to finalize this study, but would always greet me with a smile after a long day of work. This work was supported by the Earthquake Engineering Research Centers Program of the National Science Foundation (NSF) under NSF Award Number EEC-9701785, as part of the Mid-America Earthquake (MAE) Center headquartered at the University of Illinois- Urbana-Champaign. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect those of the National Science Foundation. This support is gratefully acknowledged. iii TABLE OF CONTENTS CHAPTER 1. INTRODUCTION...................................................................................1 1.1 INTRODUCTION TO THE PROBLEMS............................................................1 1.2 OBJECTIVES OF THE STUDY ........................................................................3 1.3 ORGANIZATION AND SCOPE.........................................................................5 CHAPTER 2. MECHANICS OF LIQUEFACTION........................................................6 2.1 INTRODUCTION ..............................................................................................6 2.2 TERMINOLOGY AND DEFINITIONS ...............................................................6 2.2.1 Flow Liquefaction .....................................................................................7 2.2.2 Cyclic Mobility ..........................................................................................8 2.2.3 Level Ground Liquefaction .......................................................................8 2.3 UNDRAINED STRESS-STRAIN BEHAVIOR....................................................9 2.3.1 Yield Shear Strength and Liquefied Shear Strength ...............................10 2.3.2 Soil State, State Parameter, and Steady State Line ...............................12 2.3.3 Effect of Increased Density at the Same Confining Stress......................13 2.3.4 Effect of Increased Confining Stress at the Same Density......................14 2.3.5 Effect of Mode of Shear..........................................................................15 2.3.6 Effect of Method of Preparation (Soil Structure) .....................................16 2.3.7 Effect of Grain Crushing at Large Confining Pressures ..........................17 2.4 SUMMARY .....................................................................................................18 CHAPTER 3. LEVEL GROUND LIQUEFACTION RESISTANCE USING CASE HISTORIES AND CPT..............................................................31 iv 3.1 INTRODUCTION ............................................................................................31 3.2 CYCLIC STRESS METHOD...........................................................................33 3.2.1 Evaluation of Cyclic Stress Ratio............................................................34 3.2.2 Evaluation of SPT Penetration Resistance.............................................35 3.2.3 Evaluation of CPT Penetration Resistance.............................................36 3.3 CPT BASED LIQUEFACTION RESISTANCE.................................................37 3.3.1 Liquefaction Resistance of Clean Sand..................................................39 3.3.2 Liquefaction Resistance of Silty Sand ....................................................42 3.3.3 Liquefaction Resistance of Silty Sand to Sandy Silt................................44 3.3.4 Discussion..............................................................................................45 3.4 COMPARISON OF PROPOSED CPT RELATIONSHIPS AND SPT CASE HISTORIES..................................................................................47 3.4.1 Clarification of SPT-CPT Conversion .....................................................48 3.4.2 Comparison of CPT Liquefaction Resistance Relationships and SPT Based Field Data............................................................................52 3.5 CPT BASED LIQUEFACTION RESISTANCE OF GRAVELLY SOILS............53 3.6 SUMMARY .....................................................................................................54 CHAPTER 4. YIELD STRENGTH RATIO FROM LIQUEFACTION FLOW FAILURES ...............................................................................74 4.1 INTRODUCTION ............................................................................................74 4.2 YIELD SHEAR STRENGTH AND YIELD STRENGTH RATIO........................75 4.3 EXISTING METHODS TO EVALUATE TRIGGERING OF LIQUEFACTION IN SLOPING GROUND .......................................................76 4.3.1 Poulos et al. (1985a,b); Poulos (1988) ...................................................77 4.3.2 Seed and Harder (1990); Harder and Boulanger (1997).........................77 4.3.3 Byrne (1991); Byrne et al. (1992) ...........................................................78 v 4.3.4 Summary of Existing Procedures ...........................................................79 4.4 BACK-ANALYSIS OF