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| Evolutions of P-wave velocity and thermal conductivity of granite under different thermal treatments |
| WU Xinghui1，2，3，CAI Meifeng1，2，3，REN Fenhua1，2，3，SUN Jinglai4，GUO Qifeng1，2，3，WU Xu4，ZHANG Jie1，2，3，ZHANG Liwei1，2，3 |
| (1. School of Civil and Resource Engineering，University of Science and Technology Beijing，Beijing 100083，China；2. Beijing Key Laboratory of Urban Underground Space Engineering，University of Science and Technology Beijing，Beijing 100083，China；3. Key Laboratory of Ministry of Education for Efficient Mining and Safety of Metal Mines，University of Science and Technology Beijing，Beijing 100083，China；4. Beijing Municipal Engineering Research Institute，Beijing 100037，China) |
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Abstract In the exploitation process of geothermal energy，the temperature has a significant impact on the physical properties of dry hot rock，especially the thermal conductivity of high-temperature granite after water cooling. In order to investigate the influence of the temperature and the cooling mode on the physical properties of high-temperature granite，the air-cooling and water-cooling experiments of high-temperature granite are carried out in this paper. Through investigating the conventional physical properties such as mass，volume，density and P-wave velocity as well as the thermal conductivity，the change rules of the parameters by the two cooling methods are compared and analyzed. The results show that the mass loss rate，volume increase rate，density change rate and P-wave velocity decay rate increase exponentially with the temperature. When T = 450 ℃，the change rate of granite physical properties increases significantly. Water-cooling increases the density of micro-cracks in granite，which causes further changes in the physical properties of granite. After thermal treatment，the thermal conductivity of granite decreases non-linearly by 72.85% from 3.41 W/(m·K) to 0.96 W/(m·K) with increasing the temperature from 25 ℃ to 1 050 ℃. The thermal conductivity of granite after thermal treatment is inversely related to the mass damage rate，volume increase rate and P-wave velocity decay rate in an exponential form. Comparing the physical parameters，it is found that P-wave velocity is most sensitive to the temperature，followed by the thermal conductivity and the density. Therefore，P-wave velocity can be used preferentially as an index parameter to measure the thermal damage of granite.
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2022, Vol. 41 
