2nd Ishihara Lecture: SPT- and CPT-based relationships for the residual shear strength of liquefied soils

An evaluation of post-earthquake stability of earth embankments or slopes that contain, or are founded on, soils that may liquefy requires estimating the liquefied soil׳s residual shear strength, Sr. Decisions regarding the need for expensive mitigation efforts, including ground improvement work, often hinge on the selected Sr values. This paper presents recommended SPT- and CPT-based relationships for estimating the residual shear strength ratio, Sr/σ′voσ′vo, of liquefied nonplastic soils in the field based on a review of prior case history studies, laboratory testing studies, and recent findings regarding void redistribution mechanisms. The recommended relationships provide guidance regarding the unavoidable task in practice of having to extrapolate beyond the available case history data. Limitations in the state of knowledge are discussed.