Fractal characteristics of mining-induced fractures and coal–methane simultaneous extraction technology in close-distance coal seam groups: A case study of Dong Yu Coal Mine

Accurate identification of the zoning characteristics of mining-induced fractures is crucial for achieving simultaneous extraction of coal and gas in high-gas coal seam groups. For the first mining seam of the Dong Yu Coal Mine, a quantitative characterization method for the development degree of mining-induced fractures is proposed. Integrating fractal theory with image recognition technology based on sliding window micro-unit segmentation, this method reveals the fractal characteristics of the zonal evolution of the mining-induced fracture field. Targeted technologies for simultaneous coal and gas extraction are proposed and evaluated. The results show the following: (1) Fractures concentrate heavily obliquely upward from the end of working face 1305 in the first mining seam, in the caving zone, and directly below the floor, exhibiting higher fractal dimensions and peak densities than other areas as a key gas drainage zone. (2) A simultaneous coal and gas extraction technology, termed “one working face with three roadways and dual functions for each roadway,” is proposed. In particular, high-level drainage boreholes are drilled in mining roadways (track roadway and return airway) in the first mining seam to extract pressure-relief gas from the caving and fractured zones. In the floor roadway, interception and pre-drainage boreholes drain gas from the lower adjacent coal seams; in addition, this roadway can serve as the mining roadway for the subsequent working face. (3) Field measurements show that the gas concentration remains stable at 0.05%–0.38% at the upper corner and 0.17%–0.30% in the track roadway, effectively eliminating gas over-limit issues to ensure safe and efficient mining.