Deformation and failure of rocks under 'weak' cyclic loading and incremental elasto-plasticity theory

This paper presents experimental and theoretical studies of the deformation and failure behaviors of typical soft and hard rocks during conventional triaxial tests under monotonic and 'weakly' cyclic loadings. These materials show the dilation characteristics at lower confining pressures and the brittle-ductile transition. The authors present a non-associated plasticity theory using a dilatancy function for plastic behavior under monotonic loading, and an extended multi-response theory for elasto-plastic behavior under 'weakly' cyclic loading. In these approaches, the authors treat only the strain-hardening response of geomaterials as the material behavior and not the strain-softening response, since the softening is a structural phenomenon rather than a material characteristic. The response functions are represented by Laplace Transforms The response models are applied to simulate the behavior of Oya-tuff under monotonic loading with nonlinear plastic response, and the behaviors of Funyu-tuff and granite under cyclic loading with nonlinear elastic and plastic responses, respectively.