Effect of Confining Pressure on the Mechanical Properties of Thermally Treated Sandstone

To understand the effect of confining pressure on the mechanical properties of thermally treated coarse sandstone, uniaxial and triaxial compression tests were conducted for six groups of thermally treated sandstone from Xujiahe Formation in southwestern China under confining pressures of 0-40 MPa. The test results indicate that 600°C is a critical threshold of the thermal damage of sandstone by SEM and mechanical tests. When temperature is below 600°C, few micro cracks are observed by SEM. Peak strength, elastic modulus, cohesion and internal friction angle remain constant or increase with increasing temperature and all these values decrease when temperature is above or equal to 600°C under different confining pressures. Under the uniaxial and low confining pressure (≤ 5 MPa), the failure mode shows single or multiple splitting planes and it is easier to generate complex cracks with increasing temperature. Under high confining pressure (10-40 MPa), the failure mode shows a simple shear plane after treatment at different temperatures, i.e. 25-1000°C. The results may provide guidance for rock engineering design after high temperature exposure.