Abstract: To effectively reduce the gas concentration of the tunnel coal seam and eliminate the gas outburst risk, a case study is conducted on a highway tunnel in the ChongqingZunyi section of the Lanhai National Expressway. The advance drilling and detection method is employed to accurately detect the coal seam′s storage condition and the local geological structure characteristics in front of the tunnel coal uncovering face. On this basis, the effective drilling radius and gas drainage control range are determined, and the gas drainage boreholes of the local tectonic coal seam are increased. Finally, the gas drainage is carried out using predrilling in the roof, and the drainage effect and regional antioutburst measures are tested. The results show that the method adopted reaches a good gas drainage effect and the regional gas outburst risk is effectively reduced.

Key words: large crosssection highway tunnel, tectonic seam, gas drainage, antioutburst measures, drilling radius