Liquefaction analysis of level and sloping ground using field case histories and penetration resistance

The objective of this study was to develop simple, empirical methods to evaluate liquefaction problems in level and sloping ground. Specifically, these methods include: (1) CPT-based level ground liquefaction resistance relationships for sandy soils; (2) SPT- and CPT-based relationships to estimate yield shear strength available at the triggering of liquefaction in sloping ground (i.e, ground subjected to a static shear stress); (3) SPT- and CPT-based relationships to estimate liquefied shear strength available at large deformation following liquefaction triggering; and (4) A liquefaction analysis procedure for sloping ground that addresses liquefaction susceptibility, liquefaction triggering, and post-triggering stability.; The author collected 172 level ground liquefaction and non-liquefaction case histories where CPTs were performed. 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. These relationships also use median grain size (D₅₀) to classify the cases.; The author collected 33 case histories of liquefaction flow failure where SPT and/or CPT results are available or can be reasonably estimated. These cases were back-analyzed to evaluate the yield shear strength and strength ratio mobilized at liquefaction triggering. Relationships between yield strength ratio and corrected SPT and CPT resistance were developed for use in liquefaction triggering analysis. The flow failures also were backanalyzed to evaluate the liquefied shear strength and strength ratio mobilized at large deformation. For cases with sufficient information, the back-analysis incorporated the kinetics of failure. Relationships between liquefied strength ratio and corrected SPT and CPT resistance were developed for use in post-triggering stability analysis.; Lastly, the author proposed a comprehensive liquefaction analysis procedure for sandy soils to evaluate liquefaction susceptibility, liquefaction triggering, and post-triggering stability. The procedure incorporates the proposed relationships to estimate yield 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.