Softening Behavior and Volumetric Deformation of Rocks

Abstract

In this study, a constitutive model and numerical analysis were conducted on various types of rocks under triaxial compression to determine their softening response and volumetric strain. Experimental data sets corresponding to different types of rocks were used to determine the elastoplastic material parameters and disturbance parameters of the proposed model. The disturbed state concept was utilized based on the response of the material in two states. Relatively intact (RI) and fully adjusted (FA) responses were interpolated using a state function called a disturbance. The RI and FA parts were modeled based on nonlinear finite element analysis (NFEA) and the residual strength of the corresponding material, respectively. For the RI state, the elastoplastic behavior was simulated using a hierarchical single surface (HISS) plasticity model to account for factors such as continuous yielding, volumetric change and the stress path dependence of rock. The failure surfaces used for different types of rocks were extracted from a computer program and represented in this investigation. Furthermore, the contours of disturbance (D) were depicted and the failure pattern of corresponding rock was estimated based on the distribution of disturbance values. Verification of the numerical results with experimental data sets showed a good accuracy for various types of rocks under different confining pressures.