A gradient enhanced transversely isotropic damage plasticity model for rock ‐ formulation and comparison of different approaches

The nonlinear mechanical behavior of intact rock and mass is characterized by irreversible deformation, associated with strain hardening, softening degradation stiffness. In the case stratified types like shales or phyllites, additionally depends on loading direction respect to orientation principal material directions, resulting in inherent anisotropic behavior, many cases more specifically transversely isotropic behavior. On basis a critical review several approaches for modeling proposed literature, linear mapping Cauchy stress tensor into fictitious configuration, originally Boehler [1], was identified as best choice application 3D finite element simulations. Within this framework, an damage plasticity model rock, Unteregger et al. [2], extended presented. It implemented FE-program means return algorithm it regularized over-nonlocal implicit gradient enhancement ensuring mesh-insensitive results. For validation, numerical simulations triaxial compression tests Tournemire shale, documented Niandou [3], are performed at both integration point level structural level. performance constitutive assessed its ability predict complex direction-dependent failure modes observed different confining pressures inclination angles stratification planes axial loading.