Research on the height of “two zones” in overlying strata of fully mechanized caving mining of extra-thick coal seam based on multi-source data fusion

To prevent water inrush accidents in the coal mining face caused by the development of the water-conducting fracture zone in the overlying strata to the aquifer, this study conducts an in-depth study on the height of the water-conducting fracture zone and the caving zone (hereinafter referred to as “two zones”) under the condition of fully mechanized caving mining of the extremely thick coal seam in 8514 working face of Chenjiagou Coal Mine. The overlying strata of 8514 working face are mainly composed of mudstone, sandy mudstone and siltstone, and the geological unit structure is relatively simple. The overlying strata have been significantly affected by mining activities due to the fully mechanized caving mining of the thick coal seam. Based on the integration of multi-source data such as ground drilling measurements, theoretical calculations using empirical formulas, numerical simulations (3DEC and FLAC^3D), and similar simulations, the development heights of the collapse zone and the water-conducting fracture zone are comprehensively analyzed. The research shows that: the water-conducting fracture zone height of the ZK-1 borehole is 151.71 m and the height of the collapse zone is 87.21 m; the theoretical calculation results using empirical formulas show that the height of the water-conducting fracture zone is 134.21 m and the height of the caving zone is 53.92 m; the numerical simulation analysis results (using 3DEC and FLAC^3D methods) show that the height of the water-conducting fracture is 122.6 m and the fracture-to-mining ratio is 10.66; the similar simulation analysis results show that the height of the water-conducting fracture zone is 135.7 m and the fracture-to-mining ratio is 11.8; from the perspective of safe production, the height of the water-conducting fracture zone is 151.71 m and the fracture-to-mining ratio is 12.24; the height of the collapse zone is 87.21 m and the caving-to-mining ratio is 7.03.