Effects of Coal Thickness on the Fractal Dimension of Gas Migration Channels: Laboratory and Field Study of a Gassy Coal Mine

Coal mining leads directly to changes in geophysical rock formations and upsets the equilibrium of gas concentrations in gas–liquid channels, which can cause mining disasters. In this study, based on the fractal dimension theory, the influence of coal thickness on gas migration channels in geophysical rock formations under fully mechanized mining faces was analyzed. The results demonstrated that channel boundaries become mutated in overburden. The increase in coal seam thickness affects directly the height of the gas migration channel. Under the condition of a 6 m mining height, the height of the gas migration channels developed to 60 m and the width reached 33 m. At the same time, the fractal dimension under the condition of 6 m mining height increased by 1.07 and 1.23 times compared with 4 m and 2 m. The results further indicated that optimal analyses and adjustment based upon coal thickness to determine high-level borehole arrangements can ensure safety in completing mining activities at the working face. The results provided practical and theoretical foundations for identifying high-concentration gas zones in geophysical rock formations and may serve as a feasible reference for further reducing the occurrence of geological and gas-related disasters.