Experimental investigations of compressive strength and thermal damage capacity characterization of granite under different cooling modes
XI Baoping1，2，WU Yangchun1，ZHAO Yangsheng1，2，WANG Lei3，ZHANG Baoping3，NIU Xinming3#br#
(1. College of Mining Engineering，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China；2. Key Laboratory of Insitu Property Improving Mining of Ministry of Education，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China；
3. Sinopec Research Institute of Petroleum Engineering，Beijing 100101，China)
Abstract：The thermal damage capacity for granite is different under different cooling modes，and the microfracture degree and macroscopic mechanical properties are also different. Comparative tests of the uniaxial compressive strength and surface cooling law of granite were carried out under two cooling modes of natural cooling in 20 ℃ air and cooling in thermostatic water of 20 ℃，and a heat transfer numerical simulation method under different cooling medium environments was established by introducing a thermal shock factor which can describe the damage ability of heat to rocks. Strength degradation mechanisms of granite with different cooling media were discussed from the perspective of heat transfer，and quantitative classification of thermal damage capacity is made according to the thermal shock factor. The results show that，due to that the heat transfer coefficient of thermal shock sharp cooling mode is much higher than that of natural cooling，the values of the thermal shock factor and the dynamic thermal stress under the former mode are larger than those under the later mode，which results in more serious cracking，larger density of cracks and worse deterioration of the mechanical strength of the specimen. In the thermal shock cooling mode in constant temperature water of 20 ℃，the compressive strength of granite is only 85%–90% of that in the natural cooling mode in 20 ℃ air. For different cooling modes，the evolution process and law of temperature gradient，thermal shock factor and dynamic thermal stress formed inside the granite specimen are consistent，and the maximum values always occur near the surface of the specimen. The thermal shock factor can well characterize the thermal damage ability，and the uniaxial compressive strength of granite has a good correlation with the maximum thermal shock factor. According to the evolution law of the thermal shock factor，the specific time of the most serious internal fracture of granite specimens can be determined，and the thermal shock factor can realize the quantitative classification of thermal damage capacity.
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2020, Vol. 39 
