A Micromechanics-Based Approach to the Failure of Saturated Porous Media

Abstract

This contribution is devoted to the implementation of a homogenization method for deriving the strength or failure properties of a fluid-saturated porous medium, from those exhibited by its individual constituents at the microscopic level. Within this context, a specific attention is paid to the possibility of adopting an effective stress formulation. While the case of a purely cohesive solid matrix provides the first illustrative example where the ‘effective stress principle’ as originally stated by Terzaghi is fully applicable, the analysis is then particularly focused on porous sandstones, modelled as periodic packings of cemented rigid grains. A closed-form analytical expression is thus obtained for the strength criterion of such rock materials, which proves to be a function of a generalized effective stress formed 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 microstructural parameter involved in this formulation is the ratio between the intergranular contact area and the grain cross-section area. A possible extension of the homogenization procedure in order to account for a still more realistic description of the sandstone microstructure is finally outlined.