Influence of confining pressure on deformation and strength properties of granite after high temperatures

Based on the triaxial compression tests of thirty granite samples under different confining pressures and temperatures of 25~1000℃ by MTS815.02 servo-controlled testing machine,the influence of temperature and pressure on the deformation and strength characteristics is analyzed. The test results show that: (1) The quality of rock samples decreases slightly with the increasing temperature, which decreases by only 0.364% at 1000 ℃ compared to that at 25℃. When the temperature is below 600 ℃, the volume and density have no significant change, then as the temperature rises, the volume expands with acceleration and the density decreases rapidly, and the volume expands by 5.027% and the density decreases by 5.132% at 1000℃ compared to those at 25℃. (2) After high temperature, the triaxial compression stress-strain curves of rock samples have gone through the stages of compaction, elasticity, yield, destruction, softening and residual stresses. The stiffness, peak strength, shear strength, residual strength and plastic deformation of rock samples increase with the confining pressure. (3) The cohesion decreases linearly and the internal friction angle first increases and then decreases with the increasing temperature. The shear strength shows a quadratic polynomial reduced relationship as the temperature increases. The confining pressure weakens the influence of temperature on the shear strength. This work may provide the guidance for the selection of mechanical parameters of rock in the underground geotechnical engineering.