A micromechanics-based approach to the failure of saturated porous media

This contribution is devoted to the implementation of a homogenization meth od for deriving the strength or failure properties of a fluid-saturated por ous medium, from those exhibited by its individual constituents at the micr oscopic level. Within this context, a specific attention is paid to the pos sibility of adopting an effective stress formulation. While the case of a p urely cohesive solid matrix provides the first illustrative example where t he 'effective stress principle' as originally stated by Terzaghi is fully a pplicable, the analysis is then particularly focused on porous sandstones, modelled as periodic packings of cemented rigid grains. A closed-form analy tical expression is thus obtained for the strength criterion of such rock m aterials, which proves to be a function of a generalized effective stress f ormed as a linear combination of the total stress and the pore pressure, as in the case of poroelasticity. It is shown in particular that the key micr ostructural parameter involved in this formulation is the ratio between the intergranular contact area and the grain cross-section area. A possible ex tension of the homogenization procedure in order to account for a still mor e realistic description of the sandstone microstructure is finally outlined .