Effects of temperature on fracture and damage characteristics of deep granite

Investigating the fracture- and failure-related behaviors of rock that is subjected to temperature treatment is important for handling warm rock reservoirs during deep mining of hot dry rock and processing high-level radioactive waste. In this study, we use the semi-circular bending test in combination with acoustic emission (AE) monitoring technology to examine the characteristics of fracture and damage in granite treated at different temperatures and under different fracture modes at a depth of 750 m in the Daliuhang Gold Mine in China. The results showed that the peak load and fracture toughness of granite decreased to varying extents when it was treated at increasingly higher temperatures. The high temperature substantially reduced the bonding capacity of the particles of rock, and led to the formation of a large number of microcracks that dislodged the particles of rock along the edges of the samples. The changes in the AE counts during the different loading phases can be categorized into stabilization, increase, sudden increase, and decay stages. The damage-related variable based on the cumulative AE count revealed that samples treated at and below a temperature of 300 °C were mainly damaged in the late period of loading and exhibited brittle failure. Damage began to accumulate as early as in the middle period of loading in samples treated at temperatures greater than or equal to 600 °C. The results of this study provide a useful reference for mining deeply buried granite under different temperature gradients and fracture modes.