During liquefaction, a shear-induced dilatancy mechanism may be one of the major factors that dictate soil behavior. As shear strain accumulates, this dilative tendency results in instants of excess pore pressure drop, sharp acceleration spikes, and associated regain of shear strength and stiffness in the liquefied soil. These phenomena are documented in an increasingly large body of research studies, including downhole-array earthquake records, and laboratory and centrifuge experiments. A new constitutive model based on the multi-yield plasticity concept is developed to accurately reproduce the above characteristics of soil liquefaction. The constitutive model is incorporated in a fully coupled soil-fluid Finite Element program. Calibration was performed for
medium density sand based on laboratory tests and centrifuge experiments. The centrifuge experiments included a series of tests to investigate liquefaction effects under a soil embankment. An Internet site (http://casagrande.ucsd.edu) is now available for execution of a one-dimensional version of this Finite Element program. A comparison study conducted on this website demonstrates significant difference in soil response between level-ground and sloping sites, due to the strong influence of soil dilatancy. This study also shows dilatancy as an important mechanism in limiting soil lateral spreading during liquefaction.