ABSTRACT: A constitutive model for partially saturated hard rocks is described. It is formulated within the framework of the poroplasticity of porous media. The proposed model aims to describe the main features observed in laboratory experiment, plastic deformation and anisotropic damage induced by microcracks. However, the first version of the model presented in this paper, is developed in isothermal conditions without damage. The porous is saturated by a liquid water and a gas mixture. Two yield surfaces are used to describe plastic deformations respectively related to stress and suction variations. Based on some macroscopic assumptions, a Bishop type effective stress tensor is proposed for the modeling of plastic deformation due to stress loading. The proposed model ensures the continuity of material responses from unsaturated to saturated states. Some numerical predictions by using the model are presented and compared with experimental results. The main features of the plastic behaviour of unsaturated rocks are correctly described.

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