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Energy distribution law of coal–rock combined body under confining pressure effect

Chen Guangbo, Zhang Jing, Li Yuan, Liu Fengxu, Li Tan, Zhang Guohua

Acta Geophysica

2023

Vol. 71, no. 4

1831--1843

Coal measure strata are composed of many kinds of rock layers with different properties, and the energy accumulation ability of each rock layer is different, which causes the uneven distribution of energy. In order to explore the accumulation layer of rock burst energy in coal–rock system, based on the structural characteristics and mechanical properties of coal and rock, the mechanical model of coal–rock combined body was constructed, and the calculation formula of energy distribution of coal–rock combined body was deduced. The axial compression tests of coal–rock combined body under five confining pressures (0, 5, 10, 15 and 20 MPa) were designed and carried out. The results show that: 1) Under five confining pressures, the average compressive strength of the specimens was 18.74 MPa, 20.75 MPa, 24.68 MPa, 28.02 MPa and 32.05 MPa, respectively. With the increase in confining pressure, the compressive strength also increased linearly; 2) Under the five confining pressures, the pre-peak accumulated energy of the specimens was 0.106 kJ, 0.244 kJ, 0.591 kJ, 0.758 kJ and 1.602 kJ. With the continuous increase in the confining pressure, the pre-peak accumulated energy increased exponentially; 3) With the increase in confining pressure, the coal component accumulation energy increased exponentially, followed by 0.069 kJ, 0.182 kJ, 0.440 kJ, 0.630 kJ and 1.419 kJ, and the proportion of coal component accumulation energy was 65.14%, 71.63%, 76.72%, 82.89% and 87.07%, respectively, which were all greater than 50%. Combined bodies accumulated more energy under loading conditions, most of which were accumulated on coal components, and coal components were the main carriers of energy accumulation, which played a leading role in the destruction of combined bodies; 4) The energy distribution test method was discussed and analyzed. The energy distribution test method of coal–rock combined body based on single specimen method could effectively avoid the influence of size effect and coal–rock individual difference on energy accumulation. At the same time, the test time was shortened, the test workload was reduced, and the calculation accuracy was improved; 5) The rationality and reliability of the two methods for direct and indirect determination of coal–rock component energy were demonstrated. The error rates of the two methods were 2.936%, 1.846%, 3.125%, 3.412% and 0.862%, which were less than 5%. The error had little effect on the test results. The research results have reference significance for exploring the key strata of rock burst energy accumulation and the precise prevention and control of rock burst.