Study on the development laws of overburden rock fracture in double-seam mining of abandoned mine

As mineral resources continue to be exploited, an increasing number of mines are being abandoned. However, these abandoned mines still contain significant undeveloped coalbed methane （CBM） resources, presenting immense potential value. The overburden rock fracture field formed after coal seam extraction becomes the main pathway for CBM migration in abandoned mines. Therefore, studying and understanding the development patterns of the overburden rock fracture field is of great importance for the precise development and utilization of CBM resources in abandoned mines. This paper takes the double-seam mining in the Panyi Mine Area as an engineering background and employs theoretical analysis, UDEC numerical simulation, and physical similarity simulation methods to systematically study the development patterns of the overburden rock fracture field after double-seam mining. The research results show that the fracture zone height in the upper coal seam is approximately 58.73 to 81.71 meters. When the lower coal seam advances 170 meters, key stratum 1 generates through-layer fractures, connecting previously isolated interlayer fractures and causing the upper and lower goafs to interconnect. At this point, the fracture zones of the upper and lower coal seams are connected, with the lower coal seams fracture zone developing to a height of approximately 41.8 meters and the final fracture zone height reaching about 116.64 to 139.62 meters. The overburden rock fracture development in the upper goaf can be roughly divided into two stages: during the upper coal seam mining, fractures generate, develop, and close; during the lower coal seam mining, fractures redevelop and reclose. Long-term creep effects result in a denser distribution of fractures, but their shape does not change significantly, ultimately forming a “saddle+crab shell” composite type structure for the double-seam fracture field. The research outcomes reveal the development patterns of the overburden rock fracture field in abandoned mines with double-seam mining. Based on the fracture field distribution characteristics after long-term creep, the study proposes the main pathways for CBM migration in abandoned double-seam mines. These findings can serve as a reference for the precise extraction of gas in similar abandoned mines.