Under gassy coal seam condition, the full-heading development is employed. Because of the fast heading a high rate of gas emission arises.
在瓦斯含量较大的煤层采用综掘掘进巷道，由于掘进速度快，出现了瓦斯涌出量过大的现象。
The effect of gas discharging is limited by length , diameter of borehole in coal seam and high cost of laneway development.
上述方法存在的问题是钻孔法有效抽采孔段长度短、终孔孔径小、抽采效果差，巷道法施工工期长、费用昂贵、不利于瓦斯利用。
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