【正文】 inage of gas and in gas control to prevent outbursts in coal seams. Based on the current condition of coal seams in the Panyi coal mine, we adopted a protective layer in our mining technology to drain pressure relief gas from protected seams,using RC net penetration boreholes in floor roadways, effectively reducing its gas content, pletely eliminating the danger of outbursts and achieved safe and highly efficient mining conditions.2 General situation of test areaThe Panyi coal mine is a large mine designed for 3Mt production capacity. The C13 coal seam is one of its primary and most productive coal seams, which contained a large amount of gas under high large number of outburst accidents have formerly occurred during mining, including a major gas explosion, so control over coal gas was very urgent before we could exploit this coal seam.The test area was located between the East1 and East2 mining areas, with the B 11 coal seam as a protective layer. We planned to bine mining the 21511 working face in East1 and the 23521 in East2 and called the bination 23521 instead The strike of the face is 1640 m and the trend 190 thickness of the coal seam is between ～ m, m on average and the dip angle 60130, 90 on average. The amount of gas of the B11 coal seam is , designed for 2000 t/d.The C13 coal seam is a protected layer, located 70m above the B11 coal seam. The corresponding test working face of the protected layer consists of the 21213 working face in East1 and the 23223 in East2 (called 21213/23223 bined). The strike is 1680 m (two faces in all) and the trend is 160 coal seam is ～ m thick, m on average,the dip angle 60～130 and 90 on average. The original measured gas pressure was MPa, the amount of gas (). The coal seam was also stable and its geological structure simple. By draining the pressure relief gas, the danger of outbursts in the C13 coal seam could be 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 boreholes通常,煤層的低滲透系數(shù)低，例如,平均來說,～1m2/()，它目前最大的困難在提前排出瓦斯控制在煤層中發(fā)