Modeling of dilative shear failure.

Medium-to-dense sand sheared under undrained or essentially undrained conditions shows a dilative hardening response when the stress crosses a phase transformation state and gets into the dilative zone. When the stress finally reaches a failure surface, the deviatoric stress as well as the mean normal stress may continuously develop along the surface, accompanied by an excessive but finite deviatoric strain. This behavior is termed as dilative shear failure in this text. Properly modeling this behavior has its significance in predicting the large deformations of many geotechnical structures at or near failure. This includes quantitative predictions of postliquefaction ground deformations during and after earthquakes. This paper points out that dilative shear failure is no more than a combination of neutral loading and perfect plasticity, however, under which the stress-strain relationship is still well defined. This paper presents a general framework in modeling this failure mode, identifies dilatancy as a key parameter to quantify this phenomenon, and shows examples of numerical simulation by extending the capabilities of an existing sand model.