Mechanical properties of granite at high temperature subjected to true triaxial compression

Understanding the mechanical properties of rock at high temperature subjected to true triaxial compression is significant for studying the wellbore stability in developing hot dry rock resources. In this study, true triaxial compression tests were conducted on granite specimens at different temperatures (up to 400 degrees C) and under different intermediate principal stresses (02) (up to 140 MPa). The experimental results demonstrated that the granite specimens at all temperatures transform from expansion to compression along the 02 direction in the post-peak stage under high 02. The influences of temperature on crack initiation stress (CI), crack damage stress (CD) and peak strength (0p) of granite under true triaxial stress were analyzed. It was found that the growth rate of 0p with 02 varies with temperature. The influences of temperature and 02 on the failure characteristics of granite specimens were investigated from macro-to micro-scale. The failure modes of the granite specimens change from shear to tensile-shear mixed failure with increasing temperature and 02. The failure mechanism of granite at high temperature subjected to true triaxial compression was further analyzed. Finally, a Mogi-Coulomb failure criterion with temperature-dependent coefficients was proposed for granite at high temperature subjected to true triaxial compression. The proposed failure criterion could well describe the dependence of mechanical properties on temperature for granite. This study provides a new understanding of the mechanical properties of rock under high temperature and true triaxial compression.