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| The degradation mechanism of granite after the cyclic treatment of heating and liquid nitrogen cooling |
| TANG Xuhai, SHAO Zuliang*, XU Jingjing, ZHANG Yiheng
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| School of Civil Engineering, Wuhan University, Wuhan 430072, Hubei, China |
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Abstract This paper discussed the auxiliary technique of TBM tunnelling through cyclic treatment of heating-Liquid nitrogen(LN2)cooling on granite. The granites were subjected to the cyclic treatment of 200 ℃-LN2 cooling, 300 ℃-LN2 cooling and the 400 ℃-LN2 cooling, and the numbers of cyclic treatment were 1, 3, 6, 12, 20 times, and all the treated specimens were subjected to uniaxial compression tests. Microstructure and the micromechanical properties of granites treated with cyclic treatment of 400 ℃-LN2 cooling were studied by microscope and nanoindentation technology. The results showed that, under the same times of cyclic treatment, the higher the heating temperature was, the greater the deterioration degree of granites was. The change of macroscopic mechanical properties with the increase of the cyclic treatment times could be divided into three stages: rapid change stage(0-6 times), slow change stage(6-12 times)and nearly constant stage(after 12 times). The higher heating temperature, and the more times of cyclic treatment, the failure mode of granite under uniaxial compression would be more complex. The degradation induced by cyclic treatment of 400 ℃-LN2 cooling was mainly due to the development of microcracks rather than the deterioration of mechanical properties of crystals themselves.
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Received: 25 May 2021
Published: 20 March 2022
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