The evolution characteristics of fractures in overlying rock for underground coal fires

Fractures generated in the overlying rock of coalfield fire areas can develop into air leakage and oxygen supply channels, thus helping sustain and intensify the fire. However, the formation, evolution, and distribution of such fractures are complex. This study used physical similarity simulation and numerical simulation to analyse the formation and evolution process of the underground coal field fire area at the Tanyaoqu coalmine. The first air leakage and oxygen supply channel in a coal fire area is formed when the overlying rock fractures reach the surface. The average collapse step distance of overlying rock after the formation of the first air leakage and oxygen supply channel in the research area was approximately two times that before. The length of the main fracture in the overlying rock increased gradually with coal combustion temperature. The angle between the main fracture and the horizontal plane decreased as temperature increased before the formation of the first channel and increased with temperature after the formation. When the coal combustion temperature was 600, 800, and 1000 °C, the distances from the coal seam damage position to the first air leakage and oxygen supply channel position are 122.7, 114.7, and 103.1 m, respectively.