1.Shenyang Research Institute, China Coal Technology and Engineering Group,Shenyang , China;2.State Key Laboratory of Coal Mine Safety Technology, Fushun , China

This paper proposes a gas extraction technology - super large diameter borehole gob gas extraction technology. The technology is devoted to reduce gas concentration of working face upper corner in U-shaped ventilation, solve the problem of extraction deficiency caused by the unreasonable high-level drainage roadway layout, and reduce the construction cost of using Y-type ventilation gob side entry retaining in the early stage. Based on theoretical analysis and field tests, it is concluded that the extraction is most efficient when the spacing of boreholes is 15 m or 20 m.Field application shows that, compared to conventional gas extraction, the pure quantity of gob gas extraction in the large-diameter extraction increases by 54.9% and the extraction concentration increases by 1.33 times. The technology is also superior to Y-type ventilation gob side entry retaining, which is evidenced by 12.7% reduction of average gas concentration in return air flow,and reduction of labor requirement. Applying this gas extraction technology, gas concentration of upper corner of U-shaped ventilation can be effectively controlled and buried pipe on upper corner and gob side entry retaining can be removed, which greatly improves the mining productivity.