Poroplastic damage model for claystones

Abstract The aim of this work is to propose a poroplastic damage model for claystones. Based on experimental results, this model reproduces the effects induced by degradations of the porous matrix after a mechanical loading. First, an anisotropic poroplastic damage model is formulated in order to describe the material degradations. According with the experimental observations, a plastic yield function based on the Drucker–Prager criterion is used, while considering an isotropic plastic hardening. Furthermore, as for most rocks, the plastic flow is non-associated. In order to take into account the induced anisotropy, the damage is represented by a second-order tensor. The interest of the damage elastic constitutive law is the effective stress, which allows the coupling with plasticity. The triaxial drained tests were then simulated under different confining pressures. The comparison with the experimental results is very satisfactory. Finally, the plastic damage model is reformulated in order to take into account the damage influences on the hydromechanical behaviour of the rock. Using the results of micromechanics analysis and assuming initial isotropy and microhomogeneity of the material, we obtained Biot coefficient tensor according to the damage variable. In order to quantify the influence of the damage on the poromechanics coefficient value, numerical simulations were carried out.