Research on borehole gas extraction based on the influence of mining height on the evolution of overburden fracture in working face

The evolution of fractures in mining overburden plays a pivotal role in interlayer gas migration. Therefore, a comprehensive study of crack development and distribution improve the efficiency of gas extraction. This study the west 2107 fully mechanized mining face in Weijia Mine of Gansu Province as the engineering background, Specifically, this study established numerical models of different mining heights by using the UDEC simulation software, and analyzed the relationship between the evolution of near-field fractures in the overburden of the working face and different mining based on fractal geometry theory. The optimal working face height for gas extraction was determined and validated through theoretical empirical formulas, field observations of overburden fractures, and gas extraction results. The results show that the total number of mining fractures increases with the increase of mining height, but the amplitude of increase is different at different stages, and the overburden fractures continue to develop in an "umbrella" shape around the overburden. The near-field fractures of the overburden rock at different mining heights have undergone three stages: generation, expansion and penetration, and compaction stability. Increasing mining height, smaller compaction zones. When the mining height is 4 m, the development density and range of roof fractures at 10 m and 40 m are significantly higher than those in other areas, which is consistent with the optimal position of the collaborative extraction roadway with high and low roadways.