Characterization of crack evolution and hardening-softening in rock elastoplastic constitutive models

To accurately represent crack evolution and hardening–softening in rock elastoplastic constitutive models: (1) Based on conventional triaxial compression and the Mohr-Coulomb strength criterion, the elastoplastic characterization of crack evolution and hardening–softening under plastic strain and confining pressure is examined, along with its relationships with dilatancy angle ψ, elastic modulus E, Poisson’s ratio μ, cohesion c, and internal friction angle φ; (2) Through experiments on silty mudstone, these mechanical parameters are inverted as bivariate functions of plastic shear strain γp and confining pressure σ3: ψ(γp,σ3), E(γp,σ3), μ(γp,σ3), c(γp,σ3) and φ(γp,σ3), establishing a model that describes crack evolution and hardening–softening; (3) The predictive capability of the model is validated through secondary development in FLAC3D and comparison with experimental results. The study reveals that crack volumetric strain is equal to plastic volumetric strain, and crack evolution can be indirectly quantified through ψ(γp,σ3). Disregarding elastoplastic coupling, the elastic phase of the stress–strain curve is represented by E(γp,σ3) and μ(γp,σ3), while the hardening–softening phase is described by c(γp,σ3) and φ(γp,σ3). The simulated results of crack volumetric strain and stress–strain curves closely align with experimental data, indicating that the model adequately characterizes crack evolution and hardening–softening.