Development law of water⁃conducting fracture zone in overlying rock with layered mining under strong water⁃bearing body in Barapukuria coal mine

The geological conditions of the Barapukuria coal mine are particularly complex，multiple hazards are inter⁃ twined，especially the mine water hazards pose a serious threat to safe production. The detection of the height of water⁃conducting fissure zone is closely related to the water⁃retaining mining. Controlling the development height of the water⁃conducting fracture zone is to ensure the stability of the LDT water barrier and avoid the water barrier from being broken down under the action of the confined water body. Combining with the special geological conditions of Barapukuria coal mine，the geological mining conditions of the mine show the characteristics of “three thick，two hard and one strong”，such as the thickness of the mining coal seam，the thickness of the sandstone layer on the roof of the mining coal seam，and the thickness of the overlying loose aquifer UDT. The overburden is water⁃proof⁃key layer structure type. The bedrock lacks the structural characteristics of an effective water barrier. It is proposed that the bed⁃ rock aquifer is progressively diverted with layered mining to ensure the effective water barrier performance of the LDT water barrier and block the UDT water body leakage into the mine，forming a safe mining mode of “upper protection and lower dredging” for slicing and mining of extra⁃thick coal seams under strong water⁃bearing bodies. With the help of 360° rotating downhole TV full⁃hole wall imaging system，the leakage of drilling fluid and the change of water level are analyzed. The physical simulation methods and numerical calculation simulation methods are applied to compre⁃ hensively simulate and analyze the height development law of the water⁃conducting fissure zone in the overburden and the movement and failure law of the overlying strata with different layers， different mining heights and different coal mining methods. The drilling detection work and data analysis，and the comparison of the results of phys⁃ ical similarity simulation and numerical simulation are completed. It is confirmed that the experimental simulation re⁃ sults are basically consistent with the detection data. Research shows that when the cumulative mining height is 8.5 m，the height of the water⁃conducting fracture zone in the layered mining shows a rapid growth pattern. When the cumulative mining height is 13 m to 15 m， the development height of the water⁃conducting fracture zone tends to be flat and no longer increases. The first and second⁃slice mining contributes a lot to the growth rate of the height of the water⁃conducting fissure zone. The main reason is that the first⁃ and second⁃slice mining increases the cracks in the overlying rock，and the increase of the cracks is manifested by the softening of the lithology. The height of the fracture zone and the mining thickness basically increase linearly. The height of the water⁃conducting fracture zone of the two⁃slice mining increases by about 109% of that of the first layer. With the increase of the lay⁃ er thickness，the increase of the height of the water⁃conducting fracture zone tends to increase. The belt height is dis⁃ tributed in a saddle shape as a whole. The layered and coordinated mining of the working face effectively reduces the development height of the overburden water⁃conducting fissure zone，protects the UDT aquifer from leaking， and forms a safe mining mode for the thick coal seams under strong water⁃bearing bodies in Barapukuria coal mine.