沅古坪隧道选线的岩溶水文地质问题

避开突水突泥的高风险区是岩溶隧道选线的基本出发点。沅古坪隧道穿过岩溶强发育区，为典型的岩溶深长隧道。岩溶地下河、向斜蓄水构造、两侧水库以及地下水位与顶板的高差大等是影响其隧道安全建设的重要因素，也是选线要考虑的关键水文地质问题。为更好地进行隧道东、中、西三条设计线的比选，在隧道研究区开展了1:1万的岩溶水文地质专题调查，查清研究区岩溶发育和水文地质特征，划分出岩溶地下水系统，从而比较了3条隧道线所处的岩溶水动力水平分带和垂直分带，分析隧道与地下河、岩溶泉的空间关系，并结合物探资料分析了向斜蓄水构造的影响。结果表明:东线隧道穿过地表分水岭地带，处于岩溶水动力系统的补给区和垂向分布带的季节变动带、浅饱水带，基本不与地下河管道立交，远离了流量较大的岩溶泉，降雨补给面积最小，因此，总体涌水风险最小，为最佳隧道线路。西线纵穿赤溪河上游地下水系统的中部，穿过径流和排泄区，处于岩溶水动力垂向分带的浅饱水带，并与多条岩溶管道立交，且临近西侧高家溪水库，涌水风险最大。东线隧道临近黄鱼溪水库的北段、穿过郭家界向斜储水构造核部的南段是涌水高风险区，需扩大岩溶水文地质补充调查，并在施工中加强超前地质预报研究，最大程度避免岩溶地质灾害。 

Karst hydrogeological problems in the route selection of Yuanguping tunnel

Avoiding high-risk areas of gushing water and mud is the basic principal for karst tunnel selection. The Yuanguping tunnel is a typical long and deep karst tunnel,which passes through the area with strong karst development. There are some important factors affecting the safty of tunnel construction,such as karst underground river, syncline water storage structure, reservoirs on both sides, and the large height difference between the groundwater level and the roof,,which are also key hydrological issues to be considered in route selection. To better compare and select the three design lines of the east, middle and west of the tunnel, a 1:10,000 special survey of karst hydrogeology was carried out in the tunnel working area.The karst development and hydrogeological characteristics of the working area were found out, and the karst groundwater system was divided, so as to compare the horizontal and vertical zoning of the three tunnel routes. The spatial relationship between tunnel and underground rivers and karst springs was analyzed, and the influence of syncline water storage structure was analyzed combined with geophysical data. The results show that: the east route tunnel passes through the surface watershed zone and is located in recharge area of the karst hydrodynamic system and the seasonal variation zone and shallow saturated zone of the vertical distribution zone. It basically does not intersect with underground river pipelines and is far away from karst springs with large flows, the rainfall replenishment area is the smallest, therefore, the overall risk of water gushing is the smallest, which is the best tunnel route. The west route runs through the middle of the groundwater system Ⅲ in the upper reaches of Chixi river passes through the runoff and drainage area,and is located in a shallow saturated zone with karst hydrodynamic vertical zoning. It intersects with multiple karst pipelines,and is close to the west side of Gaojiaxi reservior,with the greatest risk of water gushing. The northern section of the east route tunnel near Huangyuxi reservoir and the southern section passing through the Guojiajie syncline water storage structure are all high-risk areas for water gushing. Therefore,it is necessary to expand the supplementary survey of karst hydrogeology, and strengthen the research of advanced geological forecast during construction so as to avoid karst geological disasters to the most extent.