Research on mechanical properties and acoustic emission characteristics of sandstone under splitting loading after temperature treatment

In underground engineering, tunnels are important passages for underground wastewater, personnel and vehicles. As the surrounding rock usually experiences the splitting failure, the mechanical properties of the rock subjected to splitting loading are important for surrounding rock stability after a fire. In this study, Brazilian splitting tests were carried out on sandstone after different temperatures (25 °C to 1000 °C), and the acoustic emission (AE) signals of the rock splitting failure process were obtained. Based on the test, the thermal damage rock splitting strength and AE parameters were analyzed, and the effect mechanism of temperature on rock tensile strength was elucidated. The results show that (1) the rock tensile strength fluctuates in the range of 25–400 °C, and the deterioration effect on the tensile strength is significant when the tensile strength exceeds 400 °C. (2) The AE energy follows a power-law distribution, in which the power exponent decreases when it exceeds 400 °C, the main frequency distribution band widens, and the number of AE signals with low energy and high main frequency increases. (3) Mineral decomposition and thermal fracture degrade rock mechanical properties and fracture acoustic signals, resulting in a temperature dependence of rock tensile strength and AE parameters. The research results provide a reference for fracture analysis and stability monitoring of tunnel surrounding rock splitting failure after a fire.