An elasto-plastic damage constitutive model with double yield surfaces for saturated soft rock

An elasto-plastic damage constitutive model with double yield surfaces is developed based on irreversible thermodynamics theory and damage mechanics theory. Two kinds of plastic deformation mechanisms, including plastic friction and plastic pore deformation mechanisms, are considered. The plastic friction yield criterion is established by a parabolic open function that incorporates the volumetric deformation effect, and the motion of yield function in stress space is governed by its center position and rotation hardening rule. Meanwhile, a plastic pore yield criterion is established by adopting Gurson's criterion using the proposed friction yield model to determine the matrix deformation of porous materials. A damage variable is defined to describe the development of various microscopic defects. Comparisons between numerical predictions and experimental data of triaxial compression tests are presented with various confining pressure conditions to verify the rationality of the proposed model.