Characteristics of overburden fracture conductivity in the shallow buried close coal seam group and its effect on low-oxygen phenomena

The distribution and conduction properties of overburden fractures following coal extraction beneath a shallowly buried, proximate coal seam group are extremely complex. These fractures are a primary source of air leakage within the mining zone and contribute to oxygen-deficient conditions at the working face. Therefore, in this study, physical similarity simulation experiments are used to quantitatively analyze the distribution and conductivity characteristics of the overburden fractures during the mining of shallow buried close coal seam group. The results show that with the increase in mining distance, the high level area mainly forms breakage fracture, and its fracture aperture increases significantly, and the penetration is enhanced. The low level area gradually generates delamination fracture and connects with the high level area fracture, constituting a three-dimensional gas leakage channel between the working face, the upper mining area, and the ground surface. Moreover, the changes in the frequency, angle, and aperture of the fractures have a significant effect on the transportation and circulation of low-oxygen gas; the frequency of fractures gradually increases, the density gradually increases, the angle range gradually becomes bigger, and the aperture gradually becomes bigger, which provides a “hotbed” for the enriched storage and transportation and circulation of low-oxygen gas. This study provides a scientific basis for the prevention and control of low-oxygen and safe production in coal mines and helps to protect the life safety of coal miners.