In order to solve the low drained gas concentration problem from the gas pre-drainage borehole in the underground mine of Yuwu Coal Mining,an investigation analysis was conducted on the pre-drained gas concentration of the gas pre-drainage boreholes in different mine gateway of the mine.The paper held that the mining influences of the neighboring coal mining face would have high influences to the drained gas concentration from the gas pre-drainage borehole in the mine gateway.A method combined with the theoretical analysis and the site measurement was applied to study the pre-drained low gas concentration causes of the gas pre-drainage borehole in the mining influence area.Within the mining influence area,with the influence of the stress increased,the thickness of the rock released ring in the surrounding rock of the mine roadway would be increased.During the sealing of the pre-drainage borehole,due to the grouting section of the borehole sealed could not avoid the rock released ring in the surrounding rock,the grouting liquids were leaked along the cracking and thus the borehole sealing was failure.According to the mining influence area,a new borehole sealing method was provided to increase the borehole sealing depth and to reduce the borehole sealing depth.The practices showed that with the application of the new borehole sealing method,the drained gas concentration from the gas pre-drainage borehole in the mining influence roadway was obviously increased,the gas drainage volume fraction of near 80％ boreholes was over 30％ and the boreholes with the volume fraction over 30％ were 10 times higher than the previous boreholes.%为解决余吾煤业井下瓦斯预抽钻孔抽采瓦斯浓度低的问题,对该矿不同巷道预抽钻孔抽采浓度进行了调查分析.认为相邻的回采工作面采动影响对巷道内预抽钻孔抽采瓦斯浓度的影响最大.采用理论分析和现场实测相结合的方法,研究得出采动影响区域预抽钻孔抽采瓦斯浓度低的原因为:采动影响范围内,受应力增高影响,巷道围岩松动圈厚度增大,预抽钻孔封孔时封孔注浆段没有避开围岩松动圈,所注浆液沿裂隙泄露,造成封孔失效.针对采动影响区域,提出了增加封孔深度、减小封孔长度的新型封孔方法.实践证明:采用新型封孔方法,受采动影响巷道瓦斯预抽钻孔的抽采浓度明显提升,接近80％钻孔的抽采瓦斯体积分数能达到30％以上,体积分数在30％以上的钻孔占比将近原来的10倍.
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