Technical scheme and application of pressure-relief gas extraction in multi-coal seam mining region

A pressure relief gas extraction technical model of a typical mining area is proposed based on coal and gas simultaneous extraction theory. Flac3D was employed to model vertical stress and displacement contour plot characteristics of non-outburst coal seam (No. 4) on top of outburst coal seam (No. 2) along strike and incline directions. Field investigations were also conducted to verify the scientific nature of the simulation. The results demonstrate that gas pressure in No. 2 coal seam dropped to approximately 0.55 MPa in the pressure relief multi-coal seam. The highest expansion rate of the coal mine reached up to 2.58%. The pressure-relief angle was 76° along the incline direction and 60° along the strike direction. As the expansion rate and pressure-relief angle increased and the gas pressure decreased, a large amount of gas flowed into the gob of No. 4 from No. 2 coal seam and was later discharged through specific gas pipes, which eliminated No. 2 outburst risks. This study resulted in positive outcomes in that gas extraction time was reduced by 13.5 days, due to pressure relief, and drilling work load was reduced by 0.1161 m/t coal. This method ensures that gas is discharged from the outburst coal seam quickly and safely, demonstrating that the proposed technical model of pressure-relief gas extraction is effective in a multi-coal seam region.