Strain localization in fluid-saturated anisotropic elastic-plastic porous media with double porosity

Double porosity models applied to fissured rocks distinguish the role of the pores, which provide storage for the fluid, from that of the fissures, which provide most of the permeability. Analyses on the subject so far have considered elastic isotropic solid skeletons. One purpose of this work is to formulate, within the context of mixture theory, a double porosity framework including first anisotropic elastic solid skeletons and next anisotropic elastic-plastic solid skeletons. The framework applies to fissured rocks and partially saturated soils as special cases. For fissured rocks, fluid mass transfers between pores and fissures and scale segregration between these two types of cavities are accounted for. For partially saturated soils, the effects of surface tension and a different spatial organization of fluids are included. Then, whatever the type and degree of anisotropy, the onset of strain localization in the double porosity mixture is shown to be coincident with that of the underlying drained solid. This result thus generalizes previous findings for single porosity mixtures.