Research On The Optimization Of Diversion Tunnel Route Under The Constraint Of Karst Water Environment

In the karst area of southwest China,due to karst development and rich karst groundwater resources,it is inevitable to encounter the problems of water flooding and water inrush in the construction of tunnel construction.At the same time,due to the construction of a large amount of drainage groundwater,the karst water environment will also be caused.Water diversion project in yunnan associated tunnel digging color section along the complex geological conditions,karst development and groundwater is rich,numerous lines surrounding villages,densely populated,groundwater is a main drinking water source of local residents.In particular,the route will pass through the vicinity of wenchang palace,which is dense with karst water,and the risk of reducing flow and dredge will be extremely high in the future tunnel construction.The decrease of water volume will have a serious impact on the normal life and production construction of the surrounding residents.Therefore,the reasonable selection of the water diversion line is of great importance.Based on the analysis of water diversion project in yunnan associated tunnel digging color stretch of the basis of the geological condition and karst hydrogeological conditions,combined with the feature of line crossing area karst development,from the perspective of karst water environment change,using different prediction and evaluation method,comparing selected line karst groundwater environmental impact prediction analysis,flood water inrush risk evaluation for tunnel;By selecting the influence factors of the line,the line evaluation system was established by the analytic hierarchy process,and the optimal route scheme was selected according to the evaluation result.The main conclusions are as follows:(1)The terrain cutting is strong,the geological structure is complex,the karst development is large,and the total area of the study area is 45%.In the devonian system(D1k)dolomitic limestone,(D1q)limestone and Permian(P1)limestone,the karst development is medium to strong.Through three karst hydrogeological unit,atmospheric rainfall for the main recharge source of groundwater,replenishment way controlled by lithology,structure,overall runoff from east to west,datum line on the erhai lake and surface water system in the area become excretion.(2)The comparison route adopts the engineering form of the tunnel.The line length is 6884m(A line),5572m(B line)and 6362m(C line)respectively.There are many karst springs along the tunnel,which are large and stable.They are mainly used for drinking and agricultural irrigation and fish farming.The axis of the tunnel is only 44 m from the spring point,and the water level is higher than that of the tunnel roof 100~300m,which is highly sensitive.(3)By applying the method of rainfall infiltration,groundwater dynamic comparison research method,the three-dimensional numerical simulation method to choose water lines,influence scope,predict seepage field change,analysis of karst groundwater environment and the engineering construction.The total A line has the greatest influence on the karst water environment,the influence degree of the spring point is high,the B line is centered,and the C line is the smallest.(4)Through tunnel in southwest water inrush disaster risk assessment system to evaluate line,A line,line B and C line risk rating for the length of the Ⅳ accounted for 21%,20% and 13% of each line.The length of the risk level for Ⅲ accounted for 0%,3% and 1% of each line.There is the greatest risk of flooding in the overall B line and the minimum C line.(5)The impact of the construction of the project on the groundwater environment,the impact of the groundwater environment on the project construction,and other factors were used as the first-level evaluation indicators.A hierarchical structure evaluation model was established and combined with the characteristics of the line project to comprehensively evaluate each line.The score obtained by Line A is the largest,and has the greatest impact on the karst water environment.Line B is centered,Line C is the smallest,and the karst water environment is the least affected.