The coal seam C5 in entrance section of Yujingshan Tunnel on Chengdu-Guiyang High-speed Railway is determined to be risky because of gas outburst.In order to ensure the construction safety and avoid gas accidents,the gas drainage technology of penetrating meshy boreholes is adopted.By comparison among several schemes,the drilling field is set in left side of parallel heading,gas drainage of parallel heading and main tunnel is carried out at the same time and the control range,borehole span and endhole span of gas drainage are decided.The gas outburst elimination includes three parts,i.e.regional outburst prevention,local outburst prevention and rock outburst prevention.The value of the gas desorption index K1 and gas concentration are used to testify the effect of gas outburst elimination.The real-time monitoring results about gas concentration and air velocity based on KJ83N on-line system show that by using deadend forced ventilation with two fans,the air-conditioning requirements can be met.The systematic technology of gas drainage used in Yujingshan Tunnel is successful;and the effect of gas outburst elimination is obvious,so as to guarantee the construction safety of tunnel crossing coal seam.%成贵高铁玉京山隧道进口工区C5煤层为瓦斯突出煤层,为保证隧道施工安全,避免发生瓦斯事故,确定采用穿层网格预抽法进行消突.通过方案比选,确定在平行导坑轮廓线左侧设置钻场,平行导坑与正洞整体一次抽放,并确定瓦斯抽放控制范围、开孔间距及终孔间距.防突流程分为区域防突、局部防突和石门防突3个过程,利用瓦斯解吸指标K1值和瓦斯含量来验证消突效果.根据KJ83N安全监控系统对瓦斯体积分数、风速等的实时监测结果可知,采用双风机独头压入式通风可以满足通风要求.玉京山瓦斯突出隧道通过采用系统的瓦斯抽放技术,消突效果显著,为揭煤和穿越煤系地层施工提供了安全保障.
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