Effect of thermal loading on compressional wave velocity, Mode I fracture toughness and tensile strength

Thermal loading can impact the mechanical properties of rock. In deep excavations, for example, ventilation can result in a significant rapid cooling of the rock. In this study sandstone samples were subjected to slow heating followed by rapid cooling, referred to as thermal shock. An initial suite of tests were conducted at temperatures of 100°C, 200°C, and 300°C. In these tests, samples were subjected to a single cycle of heating and cooling and then tested. Measurements included P and S wave velocity, fracture toughness and tensile strength. Even though only small changes were seen at 100°C, further studies were conducted at this temperature because of the practical importance of this temperature range in mining and civil design. Cyclic heating and cooling was conducted at 100°C, with measurements of fracture toughness and tensile strength at 10, 15 and 20 cycles. Even though the overall results from the tree types of measurements (seismic velocity, fracture toughness, and tensile strength) are quite complicated, they can be at least partially explained by considering three types of crack density changes: a small decrease in crack density (crack healing), a small increase in crack density (blunting of macrocracks), and a large increase in crack density (rock damage).