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| Brazilian split characteristics and mechanical property evolution of granite after cyclic cooling at different temperatures#br# |
| LI Chun，HU Yaoqing，ZHANG Chunwang，ZHAO Zhongrui，JIN Peihua，HU Yuefei，ZHAO Guokai#br# |
(Key Laboratory of In-situ Property-improving Mining of Ministry of Education，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China)
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Abstract In the geothermal development of hot dry rocks，both the wellbore drilling and the heat exchange of the heat reservoir involve high-temperature rock mass subjected to different degrees of cooling and heating cycles，resulting in the failure of the wellbore or the increase of the degree of heat reservoir fracture. In order to reveal its mechanism，a rock mechanics tester and an acoustic emission monitoring system were used to study the longitudinal wave velocity of granite and the process of Brazilian split failure after different temperature cycles. The results show that. with increasing the number of cycles，the corresponding tensile strength under water cooling and natural cooling decreases gradually，and that the tensile strength of granite under water cooling is lower than that under natural cooling and the degradation degree of granite is obvious under high temperature and high cycle times. When the temperature is higher than 500 ℃，the apparent of granite samples gradually turns to earthy yellow，and the stress-time curve under cyclic cooling shows a gradual failure trend. At the same time，the samples gradually change from brittleness to ductility. The fracture of granite occurs along the central line of Brazilian disc in the low temperature stage(100 ℃–200 ℃) and at a certain angle with the disc diameter in the middle temperature stage(300 ℃–400 ℃). In the high temperature stage(500 ℃–700 ℃)，the fracture of granite presents complex and broken. It is also indicated that，in the low temperature stage，the influence of temperature cycles on the longitudinal wave velocity，intensity characteristics and deformation of granite is relatively small，while that，in the middle and high temperature stages，the attenuation amplitudes of the strength，wave velocity and other parameters of granite increase with increasing the number of cycles. The research results can provide a theoretical reference for evaluating wellbore failure and fracture patterns of thermal reservoir rock mass in geothermal development.
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2020, Vol. 39 
