Experimental investigation on the influence on mechanical properties and acoustic emission characteristics of granite after heating and water-cooling cycles

This study explores explore the failure characteristics of high temperature granite under different numbers of heating-cooling cycles. Combining a series of laboratory uniaxial compression tests with acoustic emission (AE) monitoring, it reveals the AE characteristics and damage behavior of high temperature granite in different damage stages. Increasing the number of heating-cooling cycles exponentially raised the mass-loss and volume-increase rates of the granite and exponentially decreased the P-wave velocity. These results indicate that multiple heating-cooling cycles irreversibly damaged the high temperature rock mass. Moreover, the variations in both the P-wave velocity and the stress threshold at each stage gradually plateaued after three thermal cycles. Under uniaxial compression, the evolution mechanism of microcracks in the rock was successfully described by the AE characteristic parameters and real-time spatial AE position. The cumulative AE counts and AE energy rates were consistent in different damage stages of the rock specimen. Both quantities began increasing after entering the unstable crack growth stage. As the number of heating-cooling cycles increased, the main fracture mechanism of rock rupture transitioned from mixed mode to shear mode, as evidenced by the distributions of rise angle and average frequency. Meanwhile, the gradually increasing b-value indicated that small-scale fracture events gradually dominated the rock damage. The present results can assist the design of deep geothermal-resource mining schemes and safe mining constructions.