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| Rock energy evolution and distribution law under triaxial cyclic loading and unloading conditions |
| MENG Qingbin1，2，WANG Congkai1，HUANG Bingxiang2，PU Hai1，ZHANG Zhizhen1，SUN Wen1，WANG Jie1 |
| (1. State Key Laboratory for Geomechanics add Deep Underground Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；2. State Key Laboratory of Coal Resources and Safe Mining，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China) |
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Abstract To explore the influence of the confining pressure on energy evolution characteristics of loaded rock samples，the experimental stress path of constant confining pressure and unloading axial pressure is designed by applying a constant axial displacement increment at the same time interval，and triaxial cyclic loading and unloading tests under six confining pressures are carried out using the MTS815 rock mechanics test system. A method for calculating rock energy based on the area formed by the loading and unloading curves is proposed，which avoids the energy calculation error caused by the assumption of constant elastic modulus. The characteristic energy density and energy consumption ratio are adopted to define the energy accumulation，dissipation and release behaviors of loaded rock samples，and the confining pressure effects of the energy evolution process and energy distribution law of the loaded rock sample are revealed. The test results show that with the passage from the pre-peak to the post-peak，the elastic energy ratio gradually decreases，whereas the proportion of the dissipated energy gradually increases. The proportions of both elastic and dissipated energies tend to be stable in the residual phase. The characteristic energy density of rock samples also increases with the increment of confining pressure. The energy consumption ratio，which is defined as the ratio of the dissipated energy density to the elastic energy density，can characterize the internal damage accumulation state of the loaded rock samples. In the pre-peak stage，the energy consumption ratio undergoes a change from increasing to decreasing，and there is an inflection point that corresponds to the symptom point of large-scale cracking or destruction of the loaded rock samples. The confining pressure can suppress energy dissipation and release due to the fracture or failure of rock samples，resulting in incomplete release of the elastic energy when the rock sample is damaged，and the energy consumption ratio is negatively correlated with the confining pressure.
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2020, Vol. 39 
