CPT-BASED PROBABILISTIC ASSESSMENT OF SEISMIC SOIL LIQUEFACTION INITIATION by Robb Eric Shedwick Moss B.S. (North Carolina State University) 1995 M.S. (Utah State University) 1997 A dissertation submitted in partial satisfaction of the requirement for the degree of Doctor of Philosopy in Engineering-Civil and Environmental Engineering in the GRADUATE DIVISION of the UNIVERSITY OF CALIFORNIA, BERKELEY Committee in charge: Professor Raymond B. Seed Professor Armen Der Kiureghian Professor Douglas Dreger Spring 2003 CPT-BASED PROBABILISTIC ASSESSMENT OF SEISMIC SOIL LIQUEFACTION INITIATION Copyright 2003 by Robb Eric Shedwick Moss ABSTRACT CPT-BASED PROBABILISTIC ASSESSMENT OF SEISMIC SOIL LIQUEFACTION INITIATION by Robb Eric S. Moss Doctor of Philosophy in Engineering-Civil and Environmental Engineering University of California at Berkeley Professor Raymond B. Seed, Chair The correlation of seismic field performance with in situ index test results has been proven to be a reliable method for defining the threshold between liquefaction and non- liquefaction. The objective of this research was to define in the most accurate and unbiased manner possible the initiation of seismic soil liquefaction using the Cone Penetration Test (CPT). Case histories of occurrence and non-occurrence of soil liquefaction were collected from seismic events over the past three decades. These were processed to develop improved CPT-based correlations for prediction of the likelihood of “triggering” or initiation of soil liquefaction during earthquakes. Important advances over similar, previous efforts include, (1) collection of a larger suite of case histories, (2) development of an improved treatment of CPT thin-layer corrections, (3) improved treatment of normalization of CPT tip and sleeve resistances for effective overburden stress effects, (4) improved evaluation of cyclic stress ratio (CSR) in back analyses of field case histories, (5) assessment of uncertainties of all key parameters in back-analyses of field case histories, (6) evaluation and screening of case histories on the basis of 1 overall uncertainty, and (7) use of higher-order (Bayesian) regression tools. The resultant correlations provide improved estimates of liquefaction potential, as well as quantified estimates of uncertainty. The new correlations also provide insight regarding adjustment of CPT tip resistance for effects of “fines” content and soil character for purposes of CPT-based liquefaction hazard assessment. Raymond B. Seed Thesis Committee Chair Date 2 TABLE OF CONTENTS Abstract................................................................................................................. 1 Table of Contents .................................................................................................. iii List of Figures ....................................................................................................... vii List of Tables ........................................................................................................ xi Acknowledgements ............................................................................................... xii CHAPTER 1 INTRODUCTION ........................................................................... 1 1.1 Research Statement.............................................................................. 1 1.2 Limitations of Previous Studies............................................................ 2 1.3 Scope................................................................................................... 3 CHAPTER 2 THIN LAYER CORRECTION........................................................ 6 2.1 Abstract .............................................................................................. 6 2.2 Discussion........................................................................................... 6 2.3 Example.............................................................................................. 15 2.4 Conclusion.......................................................................................... 16 CHAPTER 3 NORMALIZATION FOR EFFECTIVE OVERBURDEN ............... 20 3.1 Abstract .............................................................................................. 20 3.2 Introduction ........................................................................................ 20 3.3 Previous Research............................................................................... 21 3.4 Theoretical Foundation for Normalization........................................... 27 iii 3.4.1 Cohesive Normally Consolidated........................................ 28 3.4.2 Cohesive Overconsolidated................................................. 30 3.4.3 Cohesionless Contractive.................................................... 32 3.4.4 Cohesionless Dilatant ......................................................... 34 3.4.5 Cavity Expansion Results ................................................... 35 3.5 Sleeve Normalization.......................................................................... 36 3.6 Forward Normalization Analysis......................................................... 37 3.7 CPT vs. SPT Normalization ................................................................ 38 3.8 Summary and Conclusions.................................................................. 39 CHAPTER 4 DATA PROCESSING ..................................................................... 45 4.1 Introduction ........................................................................................ 45 4.2 Field Observations .............................................................................. 45 4.3 Strength Parameters ............................................................................ 47 4.3.1 Choice of Logs ................................................................... 47 4.3.2 Case Selection .................................................................... 48 4.3.3 Critical Layer Selection ...................................................... 48 4.3.4 Index Measurements........................................................... 51 4.3.5 Masked Liquefaction .......................................................... 52 4.3.6 Screening for Other Failure Mechanisms ............................ 52 4.3.7 Normalization..................................................................... 53 4.3.8 Thin Layer Correction ........................................................ 53 4.3.9 Processed Strength Parameters............................................ 55 iv 4.4 Stress Parameters ................................................................................ 55 4.4.1 Cyclic Stress Ratio.............................................................. 55 4.4.2 Peak Ground Acceleration .................................................. 56 4.4.3 Total and Effective Stress ................................................... 57 4.4.4 Nonlinear Shear Mass Participation Factor (rd) ................... 58 4.4.5 Moment Magnitude ............................................................ 60 4.5 Data Class........................................................................................... 60 4.6 Review Process................................................................................... 61 4.7 Conclusions ........................................................................................ 62 CHAPTER 5 RELIABILITY ANALYSIS WITHIN A BAYESIAN FRAMEWORK ....................................................... 66 5.1 Abstract .............................................................................................. 66 5.2 Introduction ........................................................................................ 66 5.3 Bayes Rule.......................................................................................... 67 5.4 Uncertainties in Liquefaction/Non-Liquefaction Data.......................... 68 5.4.1 Data Treatment ................................................................... 69 5.5 Limit-State and Model Formulation .................................................... 70 5.6 Bayesian Updating .............................................................................. 73 5.7 Sampling Bias..................................................................................... 74 5.8 Reliability Analysis............................................................................. 75 5.9 Summary ............................................................................................ 76 v CHAPTER 6 LIQUEFACTION TRIGGERING CORRELATIONS ..................... 78 6.1 Background......................................................................................... 78 6.1.1 Deterministic Correlations .................................................. 78 6.1.2 Probabilistic Correlations.................................................... 80 6.2 Database ............................................................................................. 80 6.3 Probabilistic Presentation of Results.................................................... 91 6.4 Deterministic Presentation of Results .................................................. 92 6.4.1 Probability and Determinism .............................................. 99 6.5 “Fines” Adjustment............................................................................. 99 6.6 Duration Weighting Factor.................................................................. 105 6.7 Final Correlation................................................................................