Research On Engineering Hydrogeological Conditions And Route Optimization In Xiaoyantang Segment Of Mid-yunnan Water Diversion Project

The length of Mid-Yunnan Water Diversion Project is 848.18 km. This project Start from is set in Qinde, Diqing State and the end site is set in Mengzi, Honghe State, among which Xiaoyantang segment is located at the end of the project. Geologic structure and karst stratum of the segment is quite complicated. Complex karst hydrogeological conditions may change the environment of groundwater and have an effect on the spring points, well points and water source in the process of tunnel engineering construction. At the same time, it could cause environmental geological hazards, such as flood water inrush. It is necessary to put forward more reasonable suggestions for the optimization of the water diversion lines.Based on geological environment conditions of the Xiaoyantang segment, three diversion routes scheme(route C1, route C2, route C3) is preliminary designed through the analysis of the complicated hydrogeological condition. Considering the influence on groundwater environment and engineering construction safety, different prediction methods are used to predict each index of the lines. A mathematical model for karst area of the preliminary line was established for the comprehensive evaluation of engineering hydrogeological problems. In the end, the optimal water diversion route is proposed. The main results of this study are as follows:(1) Lujiang karst water system is classified as the primary karst water system, its main recharge is uncovered karst area. It can be divided into two independent secondary karst water systems according to the discharge data of Zhadian River, Jijie River-Datun Sea. Zhadian River karst water system(Ⅰ-1). Groundwater flow from south to north exposed a large number of springs that total emissions is 900 L/s. Zhadian River karst water system(Ⅰ-1) is the main domestic and production water of local residents; The groundwater flow from northwest to southeast of Jijie-Datunzhen karst water system(Ⅰ-2) is controlled by structure and rock distribution. The groundwater discharge is in the Jijie River, Datun Sea, Changqiao Sea and its tributaries in linear.(2) In the Xiaoyantang segment, the mountain ranges rise and fall and the topography is steep undulating terrain, steep mountains. The tunnel scheme is reasonable and feasible via the analysis of three schemes(the round, deep rift and tunnel scheme). Therefore, the three diversion tunnel lines are set: line C1, line C2 and line C3. The tunnel construction safety evaluation index is constituted by water inflow, external water pressure and risk evaluation results of tunnel gushing, and the groundwater environment impact assessment indicators is constituted by seepage field、 radius of influence. Other factors evaluation indicators mainly includes natural environment, social environment, construction conditions and construction cost.(3) The qualitative judgment of hydrogeological problem is at the beginning of the line engineering: Route C2 has the largest influence on groundwater environment and construction safety compared with route C1 and route C3, route C1 and route C3 also have a certain negative influence on groundwater environment and construction safety.(4) The theoretical formula calculation and numerical simulation method were used to predict and analyze Xiaoyantang water diversion engineering section of the proposed circuit area, seepage field evolution is obtained at the beginning of each index. The tunnel flood water inrush risk evaluation system is quoted in the southwest of China to analyze the risk of water inrush at the beginning of the fitting line, and evaluate the possibility of potential flood water inrush disaster. In general, route C2 has the greatest influence on groundwater seepage field; Route C1 has the greatest risk degree to karst tunnel flood water inrush disasters; Route C3 has the minimal impact on construction environment. Basing on the respective comparison and analysis of each index to tunnel construction safety, groundwater environment impact, The analytic hierarchy process(AHP) was used to establish a comprehensive evaluation system to evaluate the influence of the index at the beginning of three lines selection.(5) The comprehensive evaluation system was established with the Analytic hierarchy process(AHP) operates groundwater environment impact factors of three quasi routes. The results show: Route C2 has the largest influence on groundwater environment compared with Route C1 and Route C3. Route C3 was recommended as construction program through the analysis of the comprehensive evaluation results among the tunnel construction safety and groundwater environment impact factors.