Modelling of Localisation at Finite Inelastic Strains in Fluid Saturated Porous Media

Quasi-static finite strain localisation phenomena in fluid saturated soils are studied. The governing equations at the macroscopic level arc derived in a spatial and a material setting. The constituents arc assumed to be materially incompressible. The elasto-plastic behaviour of the solid skeleton is described by the multiplicative decomposition of the deformation gradient into an clastic and a plastic part. The effective stress state is limited by the Druckcr-Prager yield surface. A particular “apex formulation” is advocated. The fluid is assumed to obey Darcy’s law. Numerical examples highlight the developments. Negative water pressures, which are important for strain localisation analysis of undrained water saturated dense sands, are obtained and their values are critically discussed.