Optimized Design on High Level Borehole in Roof of Coal Mining Face in Coal and Gas Outburst Mine

In order to improve the gas drainage rate, based on crack development features of the surrounding rock in the coal mining face and the gas flow law, the UDEC numerical simulation software was applied to simulate the crack development law of the overburden strata during No.342 coal mining face in Qinan coal mine pu shing forward and an optimized design plan of high level boreholes in the roof of the coal mining face was provided. The study results showed that when the pushing for ward speed of the coal mining face was 5 m /d, the crack development and gas accumulation zone with a distance of 12 ~ 22 m to the seam roof would be a layer contr 0l scope of the high level boreholes. An inclined control scope of the high level borehole was optimized to have a distance of 9 ~ 36 m to the air return gateway and a cr oss distance of the boreholes in the drilling site would be 35 m. The high level boreholes in the roof of No.342 coal mining face in Qinan Mine were designed and const ructed based on the optimized plan. The max gas drained concentration of a single borehole was 84%, the gas drainage rate of the high level boreholes was over 50%， the gas volume fraction of the return current in coal mining face was controlled below 0.6% and the safe mining of the coal mining face was ensured.