An elastoplastic damage model for stratified rocks using Pietruszczak–Mroz anisotropic theory

The mechanical properties of stratified rocks are closely related not only to the stress state but also to the inherent structural anisotropy, which can be represented by the occurrence of bedding planes. This research aims to enhance the understanding of the anisotropic deformation and failure behaviors of stratified rocks by proposing a novel coupled elastoplastic-damage constitutive model. In this constitutive model, a scalar anisotropic parameter (stress-structure mixed invariant) based on the Pietruszczak–Mroz anisotropic theory is incorporated into a nonlinear yield surface, which accounts for the combined effects of the stress state and bedding structure on the anisotropic strength behaviors of stratified rocks. A damage-driven function governs the expansion and contraction of the anisotropic yield surface in the pre-peak strain hardening and post-peak strain-softening regions. The strength and deformation characteristics under multiaxial stress conditions are represented by incorporating the Lode’s angle into the yield and plastic potential functions. Numerical simulations are conducted to facilitate a comparison with the conventional and true triaxial compression test data for several stratified rocks. The simulation results demonstrate good agreement with the test data, validating the effectiveness of the proposed constitutive model. This study provides theoretical and technical support for addressing engineering challenges involving stratified rocks.