Gas pressure relief rule of overlying coal seam induced by fully mechanized top coal caving in long working face

We study the effect of super-length fully mechanized top coal caving face of 15# coal seam on gas pressure relief of 3# coal seam which is 138.5 m above 15# coal seam in NO. 3 mine of Yangquan by means of numerical simulation and field measurement. The results indicate that the full pressure relief takes place in 3# coal seam on the condition of mining 252 m-long fully mechanized top coal caving face of 15# coal seam. In the advancing direction of working face, the full pressure relief boundary of 3# coal seam is 35 m behind the working face of 15# coal seam, and the full pressure relief angle of corresponding advancing direction is 75.8°; The pressure of 3# coal seam in the range between 12 m from the upper end inside the working face and 29.2 m from the lower end is fully relieved in the inclined direction of working face, and the full pressure relief angles of both upper and lower ends in the corresponding inclined direction are 85° and 78.1°, respectively. The gas extraction rate of full pressure relief area in 3# coal seam is up to 88.43%, without any coal and gas outburst happened during mining. The study results indicate that the mining of 15# coal seam can efficiently eliminate or decrease the threat of coal and gas outburst and gas overrunning, and the safe-and-high-efficient co-extraction of coal and gas is realized.