Abstract: The gas (methane) concentration in the upper-corner of coal mining face was always higher extremely than the limit after releasing the pressure of the lower coal seams group, and the gas in the bottom of goaf and among the supports also could not be drainaged in time. To address these problems, a new auxiliary technology of the roof drainage tunnel for gas drainage in goaf was developed.The technology is characterized by inner interlocked oblique drilling. According to the evolution law of roof collapse and drill hole form, the gas was drainaged from the upper-corner, among the supports and the bottom of goaf. The drainage effect of the technology was investigated in the coal mining face of 2203 in Gaojiazhuang mine. The test results show that the average volume fraction of gas is 15.1%, which increases by 1.3 times as compared with the single drainage technology of the roof drainage tunnel, that the average net gas amount is 18.61 m³/min, which increases by 1.9 times, that the superposition gas drainage efficiency is 50%, and the drainage volume accounts for 83% of the total gas emission from adjacent layers and the goaf, and that by using the technology, the volume fraction of gas in the air return way and upper-corner of coal mining face is limited to 0.6% or lower, and the smooth mining of working face is effectively guaranteed.

Key words: high level gas drainage gateway, seam groups, upper corner, oblique drilling, gas exceeding, mixed extraction rate