Dynamic tensile strength and failure mechanisms of thermally treated sandstone under dry and water-saturated conditions

To study the tensile strength and failure mechanisms of rock with hydro-thermal coupling damage under different loading rates, a series of static and dynamic splitting tests were conducted on thermally treated sandstone under dry and water-saturated conditions. Experimental results showed that high temperatures effectively weakened the tensile strength of sandstone specimens, and the P-wave velocity declined with increasing temperature. Overall, thermal damage of rock increased gradually with increasing temperature, but obvious negative damage appeared at the temperature of 100 degrees C. The water-saturated sandstone specimens had lower indirect tensile strength than the dry ones, which indicated that water-rock interaction led to secondary damage in heat-treated rock. Under both dry and water-saturated conditions, the dynamic tensile strength of sandstone increased with the increase of strain rate. The water-saturated rock specimens showed stronger rate dependence than the dry ones, but the loading rate sensitivity of thermally treated rock decreased with increasing treatment temperature. With the help of scanning electron microscopy technology, the thermal fractures of rock, caused by extreme temperature, were analyzed. Hydro-physical mechanisms of sandstone under different loading rate conditions after heat treatment were further discussed.