Studies on the Influencing Factors of Gas Emission in a Steeply Inclined and Ultrathick Coal Seam Working Face

To determine the factors affecting the gas emission in the working face during the horizontal sublevel mining of steeply inclined and ultrathick coal seams (SIUTCSs), the gas emission sources were identified and evaluated using the analytic hierarchy process (AHP), and the gas emission quantity was calculated using a prediction model. Sobol sensitivity analysis was then conducted on the influencing factors involved in the model to determine their influences on the working face gas emission. The AHP analysis found that the pressure relief area in the lower section is the main gas emission source of the working face, and the adjacent coal seams, old goaf, and rear goaf are not. The gas emission prediction model exhibits good accuracy. The calculation results suggest that the gas released from the lower section coal body accounts for 44.16-50.44% of the total gas emission quantity of the working face, and thus, it is the main gas emission source. The Sobol sensitivity analysis reveals that the dip angle of the coal seam has the greatest influence on the absolute gas emission quantity of the working face with a significantly larger sensitivity than those of other factors. The comprehensive sensitivity data analysis also suggests that the lower section coal body is the major contributor to the gas emission of the working face. Our work further puts forward a technical system of ultrahigh pressure hydraulic "drilling-slitting-pressing-draining" integrated antireflection enlarged gas extraction for controlling the gas emission from the coal body at the bottom of the SIUTCS. The engineering test demonstrates that this system can increase the permeability of the coal body and significantly improve the gas extraction efficiency of the coal body in the study area.