【正文】 eliminated and the amount of gas was effectively prehensive，mechanized cover caving coal mining technology been adopted for this working face, which was signed for 5000 t/d.3 Drainage principle of pressure relief gasDraining of pressure relief gas is referred to as protective layer mining technology. When we mine coal seams in outburst coal mines, we should first mine the nonoutburst or low risk outburst coal seams as protective layers, where the outburst coal seam is then called the protected layer. With protective layer mining, the coal and rock mass among the roof and floor moves and deforms within certain limits,which causes stress changing. Fracture fields are redistributed, ground stress is reduced, the coal seam expands, the coal seam permeability coefficient increases and drainage condition are created for pressure relief gas in the protected coal seams. In the case of the Panyi mine, we drilled penetration boreholes or carried out surface well drilling to drain the pressure relief gas, which caused the amount of gas and pressure to decrease significantly and the coal mass turned hard. Naturally. eas pressure reduced to below , the amount of gas reauced to below a 6m3/t and the coal consistency coefficient rose 48%100%.At the end, the danger of outbursts was pletely eliminated from the protected layers and conditions for safe and highly efficient mining had been achieved. Drainage indices of pressure relief gas in the different ore areas are shown in Table 1.4 Drainage methods of pressure relief gasDrainage methods of pressure relief gas consist largely of draining gas from the protected layers affected by mining. The space between the protective working faces 23521 and 21213/23223 was about 70 m, which is really a long distance below the protective layer mining. We have often used surface well drilling and upper penetration boreholes located in floor roadways to drain pressure relief gas from the underside of the protective mining layer. Surface well drilling is unreliable and we often used penetration boreholes. The design of penetration boreholes includes the construction of a floor roadway, a suction drilling field and upper penetration boreholesAll construction activities should be pleted before starting mining the protective layer and we should ensure that the pressure relief gas has been drained simultaneously with mining the protective layer. Design and construction of the floor roadwayBased on the occurrence of coal strata and concrete geologic conditions, the floor roadway was located 1020 m below the C13 coal seam in a good lithology rock bed and 4656 m from the protective the one hand, this position assured safe excavation, avoided gas inrush from the C13 coal seam and prevented the excavation of another coal seam by mistake. On the other hand, this location did not affect the mining of the B11 coal seam and assured normal functions for gas draining. The floor roadway was located in the middle of the working face of the protected layer on the strike where,in principle,one should insist on avoiding forming down proportion of the section of the floor roadway was designed for 6 m2 Design and construction of the suction drilling fieldAt working face 23223, 51 fields had been constructed west forward and away from the stopping line in the floor roadway under the C13 coal seam. In the pressure relief area, a field was set every 40 m, so the pressure relief area of face 21213/23223 in the protected layer needed 39 fields in all. According to the pressure relief angle, non pressure relief areas were present in the protected layer, with a field every 10 m, so that the non pressure relief areas of face 23223 in the protected layer needed only three fields and nine in face 21213. The drilling field was perpendicular to the floor roadway,with a length of 5m and a net section proportion of m2 Boltshotcrete support technology had been adopted. Design and construction of upper penetration boreholesEvery drilling field had 4 holes set on the strike in the pressure relief area. The space between holes was 40 m, which was oriented on the middle of the thicksurface