Experimental investigation on mechanical behaviors of Nanan granite after thermal treatment under conventional triaxial compression

Understanding the mechanical behaviors of granite after high temperature exposure and under confining stress conditions is an important issue in deep rock engineering projects such as the mining of deep underground solid mineral resources, deep geothermal energy exploitation and deep nuclear waste repositories. In this research, conventional triaxial compression experiments were conducted on Nanan granite after thermal treatment from 200 °C to 600 °C. Based on the experimental results, the influences of pressure and temperature on the deformation and strength characteristics were analysed. The physico-mechanical change mechanisms of the heat-treated granite were revealed by optical microscopy. The test results show that under 600 °C, granite volume increases by 4.11%, whereas the mass and density decrease by 0.28% and 4.21%, respectively. Average values of triaxial compressive strength and elastic modulus, cohesion and internal friction angle all reduce with temperature, decreasing rapidly by 54.99%, 39.81%, 49.39% and 27.51% from 500 to 600 °C, respectively. Granite specimens are less brittle and have higher ductility and plasticity as the temperature increases. However, confining pressure improves the mechanical properties of granite. Optical microscope images show that microcracks in granite specimens are generated and extend gradually with temperature, causing the deterioration of the physico-mechanical behaviors of heat-treated granite.