A coupled thermo-mechanical damage model for granite

With the increasing demand for mineral and energy resources, deep underground operations in mining, oil and gas industries become more frequent. This also resulted in problems associated with high temperature and pressure (HTP) that rock is exposed to in deep underground conditions. It is therefore imperative to understand and correctly model the coupled thermo-mechanical (TM) behavior of rocks for better and safer designs. For this purpose, based on the Weibull distribution and Lemaitre's strain-equivalent principle, a framework for the coupled thermo-mechanical (TM) damage model for granite is developed to simulate the deformation and failure process of rock under the high temperature and pressure (HTP) conditions. The thermal damage caused by the temperature change and the mechanical damage caused by high pressure were analyzed, and a nonlinear coupled total damage parameter is proposed in this study. The Weibull distribution parameters involved in the damage model are derived by combining the geometric conditions obtained from the conventional triaxial compression tests. In order to compare the performance of the proposed damage model, Drucker-Prager failure criterion is used as an example in the nonlinear TM damage model. For the validation of the proposed model, test results for granite samples at various temperature and confining pressures were compared in which the theoretical results are found to be in a good agreement with the experimental results. The proposed coupled TM damage model can be used in conjunction with any other failure criteria to account the damage evolution under HTP conditions.