Liquefaction Analysis of Level and Sloping Ground Using Field Case Histories and Penetration Resistance

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 nonliquefaction 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 50 ) to classify the case histories.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.National Science Foundation EEC-970178