Abstract
A development of overlying strata fractures and an unknown distribution of the two zones, which results from a strong shock tendency roof short-distance coal seam group mining, are the main problems faced by Xiashijie Coal Mine. Consequently, an experiment has been conducted; here are the steps: designing an underlying strata development law and the two-zone distribution physical similarity simulation test under the short-distance coal seam group combined mining, using the BT-AE to comonitor the fracture development law and the distribution characteristics of the caving zone and the water-conducting fractured zone, and combining with 3DEC comparative analysis. The results show that after the coal seam mining is over, the number of overlying fractures increases with depth, controlled by the mining stress field in the direction of 115° west from north to west. The direction of overlying fracture is mainly concentrated in the area of 300° ~30°; the overlying fracture angles eventually develop to 81° and 74°, increasing by 15.7% and 8.8%, and the caving ratio and cracking ratio are 4.87 and 17.75. After comparing with the numerical calculation results, the reliability of the two zones obtained by the physical similarity simulation test is verified. The AE analysis results show that the “release-accumulate-release” energy evolution process of overlying rock fracture under mining conditions has a phased relationship with fracture expansion. The energy positioning results are consistent with the distribution of BT observation cracks, and the large energy events are mostly concentrated in the collapse zone, indicating that AE has the practicality of disaster warning. The results of this study provide scientific guidance for water-preserving mining under the combined mining of coal seams with a strong impact tendency roof in Xiashijie Coal Mine.
Highlights
As an important industrial raw material in China, coal resources will not change their dominant position for a long time
After the coal seam group stoping, the collapsed zone and waterconducting fractured zone eventually developed to 70.6 m and 257.4 m, and the caving ratio and the cracking ratio are 4.87 and 17.75, increasing by 15.7% and 8.8%
The comprehensive analysis of borehole TV monitoring and acoustic emission monitoring shows that after the combined mining of deep roof coal seams with a strong impact tendency, the average height of the final collapse zone obtained from the physical similarity simulation test is 70.8 m, and the average height of the water-conducting fractured zone is 257.7 m
Summary
As an important industrial raw material in China, coal resources will not change their dominant position for a long time. Huang et al [15] combined numerical calculation model with physical simulation and theoretical analysis and concluded that the evolution of overlying strata cracks is affected by the distance between coal pillars in different sections. In this paper, aiming at the joint mining of close-range coal seams with a strong impact tendency in Xiashijie Coal Mine, the method of physical similarity simulation test is used, the law of crack development and the distribution of the two zones are obtained through the drilling TV and acoustic emission monitoring system and establish a 3DEC numerical calculation model to verify it and provide a scientific basis for the safe production of Xiashijie Coal Mine and the protection of water resources
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