Research on the effect of coal seam inclination on gas migration channels at fully mechanized coal mining face

To investigate the mechanical evolution progress of mining-induced pressure-relief gas migration channel in overlying strata fissure at fully mechanized mining working face, physical similarity simulation tests were conducted to experimentally and numerically evaluate the mining process of a coal mine in Heshun, Shanxi Province. The profiles of the gas migration channels were mathematically modeled based on the theory of elliptical zone of mining-induced fissure, using the dip angle of coal seams of working face as the key parameter. The impacts of dip angle of coal seams on the evolution of pressure-relief gas migration channel in overlying strata fissure at the main mining working face were analyzed. Results suggested that the increase in the dip angles of coal seams could reduce the height of the three zones and could expand the average weighting interval; the gas migration channels were formed at lower positions in the overlying strata, resulting in the lower height, width, caving angle, and range; in addition, with the increase of the dip angle, the segregation and propagation rates of the gas migration channel gradually increased, and the fractal dimensions of coal seams are measured in between 1.68, 1.69, and 1.71, displaying an increasing trend. On-site high-level boreholes were arranged to validate the laboratory results. Based on the monitoring, the gas extraction through the high-level borehole field reached 49.94~89.88% of the total gas emission. In general, the average concentration of gas in the upper corner is maintained below 0.27% and the average concentration of gas in the return airway is maintained below 0.32% so as to ensure a safe and an efficient mining environment. The study contributes to the theoretical basis for identification of pressure-relief gas enrichment areas in overlying strata under the effect of dip angle of coal seams.