Thermal acoustic emission characteristics and damage evolution of granite under cyclic thermal shock

In the process of geothermal energy extraction, the dry heat rock reservoir will be in the state of cyclic heating and water cooling for a long time. Therefore, it becomes important to study the effects of cyclic heating and cooling treatments on rock damage. In this context, the present study aimed to study the damage evolution process of rocks under cyclic thermal shock. In this paper, granite specimens were subjected to cyclic heating at the target temperatures of 200, 300, and 400 °C and cooling treatments using surface water spraying. The changes in the rock damage process during each heating cycle were monitored using the acoustic emission technique, and the damage mechanism and crack development mechanism of granite under cyclic thermal shock were discussed. The results show that granite will enter the rapid damage stage when it reaches a certain number of cycles (200℃, 300℃, 400℃ corresponds to the 16th, 8th, and 6th cycles, respectively) during the hot and cold cycling process the acoustic emission characteristics show a similar regularity: the inflection points a, b, c, and d appear near 40 °C, 150 °C, 240 °C, and 300 °C, respectively, when the acoustic emission signal becomes active and the cumulative ringing count increases rapidly, and the higher the heating temperature, the number of cycles when the granite enters the rapid damage stage and the temperature threshold for crack generation is advanced, when the heating temperature is 400 °C, the damage threshold point b and c is about 10 °C earlier than 300 °C. In addition, as the thermal cycle temperature and the number of cycles increased, the degree of damage to the rock intensified, and the width and density of the cracks on the surface of the granite also increased.