| Abstract: | Dynamic stability of undrained, simple-shear deformations on water-saturated granular soil specimens is discussed. The soil is described by a 2D-flow theory of plasticity for frictional and dilatant material. Contractant material becomes unstable (liquefies) at the state of maximum shear stress, whereas dilatant material becomes unstable after the state of maximum effective stress obliquity is reached in the softening regime of the background drained behaviour. In both cases the correct evolution equations for the growth coefficient of the instability are derived and compared with the results of the inertia-free formulation of the problem. |
