Effect of temperature on physical, mechanical and acoustic emission properties of Beishan granite, Gansu Province, China

The study of the influence of temperature on granite's physical and mechanical properties is significant to deep geotechnical engineering such as nuclear waste disposal engineering. The granite samples were taken from Beishan of Gansu Province, China, a candidate site for a high-level radioactive waste repository. In this paper, thermal damage on Beishan granite under different temperature (25 °C, 200 °C, 300 °C, 400 °C, and 500 °C) was studied to investigate the thermal effect on physical and mechanical properties. Uniaxial compression tests, ultrasonic velocity, acoustic emission (AE) monitorization and scanning electron microscope were adopted. The results showed that: (1) a temperature threshold of 300 °C was recognized, with the increasing temperature, the peak strength, P-wave velocity, and mass loss ratio of the granite decreased sharply. (2) combining with the scanning electron microscope results, the changes in the growth of thermal cracks due to the heating of granite at different elevated temperatures indicated the cracks in the rock increased and gradually formed a fractures zone eventually leading to rock failure. (3) The granite sample was a brittle splitting failure when the temperature was below 200 °C, the failure of granite sample presented shear failure once the temperature exceeded 200 °C (4) The accumulated AE counts increased when the stress reached σ ci (crack initiation stress) and increased significantly when the stress reached σ cd (crack damage stress). The higher the temperature was, the more seriously the granite samples were damaged.