| In the progress of tunnel development, especially the karst areas in southwest of china, there are many tunnels encountered inundation of the groundwater. Then there be over90%land are karstregions in Shizhu, Qianjiang and Xiushan of Chongqing. When tunnel cross the strong corrosion karst region, it would be threatened by the groundwater burst. The G65freeway which from Chongqing to Hunan would arrive Xiushan, and it have to build a tunnel through the Pingyanggai mount. As a synclinal construction including an abundant groundwater in the karst region, the development of the karst have many special characteristics. For example, the underground rivers are well-developed, and the tunnel is under the elevation of the underground rivers. Then it is easy to appear roof fall, water burst and slurry burst. So it is significative to research the impact to the groundwater environment and local Production and Life what result from Pingyanggai tunnel’s construction, and it can take a sample to the tunnel bulding in the similar hydrogeologic condition areas.The Pingyanggai tunnel of G65’s building bring a serious influence to the groundwater resources. Through the prediction of water burst in the prospect and verifying in the construction time, This paper analyse the hydrogeologic condition and the change by the tunnel building and take the conclusions following.Firstly, the Pingyanggai syncline is a independent karst hydrogeololgy system, having the characteristics of "a mountain have a peak and two valleys" in the south and "a mountain have three peaks and two valleys"Secondly, the Pingyanggai synclinal construction which including an abundant groundwater have a obvious boundary. On the middle and top of the east and west mountain, there are emergence water proof boundary what make up of silurian system’s shale. The planation surface at the elevation of800to900meters is the main recharge area of Pingyanggai synclinal construction, and it have a significant influence in the appraice in hydrogeololgy of tunnel water burst. The planation surface at the elevation of800to900meters is easy to suffer Karst collapse and water burst, and it taking the most attention in the exploration.Thirdly, the west of the Pingyanggai syncline’s karst development is subtertanic to east. There are three underground rivers exit in the east. first, the underground river which cross Shibanshui, Dashuijing, Miaolongtang and Niulang cave in the Tld+j washy stratums. Second, the underground river which cross Huixingshao, Shibanshui, Bajiaoshui and Longdong river in the P2c+w washy stratums. Third, the underground river which cross Yaojia vave, Baijia cave, Shendongyan, Yangquewan and Yanmenkou in the Plm+q washy stratums. In addition, there is a hidden underground river in the deep of the syncline’s core.Fourthly, Pingyanggai tunnel through Pingyanggai syncline’s washy construction, the engineering geological condition and hydrogeologic condition are complex, The karst development is abundant,. There is underground rivers exist above the top of the tunnel at50-100m and under the bottom at40-70m. the tunnel’s building would alter the original underground water system and lead to engineering geological problems, such as water burst, slurry burst, boil sand, roof fall and Karst collapse. It is hard to handle the problems and it need high cost. The problem would pullback the tunnel’s construction, delaying the project, even leading to water resources exhausted in the surrounding several kilometres, making local residents and livestorks’s drinking become difficult, then damaging the local’s entironment badly.Fifthly, in the build of the tunnel, there are13zones happen water or silt burst, and four zones have serious trouble, for instance, ZK38+770-ZK38+820have several water and silt burst, reducing the surface water largely, leading to water resources exhauste and proving the influence of the tunnel to the synclinal construction.Sixthly, the exploration show that the tunnel project are influence by the synclinal construction badly, and it is easy to suffer water and silt burst. It is extremely serious in the construction. It is irrational judged by the hydrogeologic condition. The original K line next to the BK line, and they are similar to each other in the geological conditions, the Karst problems are highlight in the project. If raise the tunnel’s elevation, it would keep away from the problem of water and silt burst. Sevenly, Karst water tunnel across the synclinal structure, the elevation in the level of the line near the karst pipes, karst issues outstanding, the tunnel construction will change the existing underground river system, resulting in large-scale sudden gushing mud disaster, the program selected in the future in line attention should be paid. |
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