Stability and bifurcation of undrained, plane rectilinear deformations on water‐saturated granular soils

Stability and bifurcation of plane‐strain, undrained, rectilinear deformations on water‐saturated granular soil specimens are discussed. The soil, sand or normally consolidated clay, is described by a 2D‐flow theory of plasticity for frictional material with non‐associated flow rule. Contractant material become unstable (liquefies) at the state of maximum deviatoric stress. For dilatant material the dominant failure mode is shear banding that occurs close to the state of maximum principal effectivestress ratio. The theoretical findings are supported by and are used to explain existing experimental results.