Identification of the karst water flow system and its application in the tunnel line selection of water diversion projects

Abstract

A critical water diversion project may face serious water inrush problems during tunnel construction when it crosses the carbonate rock formations of Julongshan syncline.Characteristics of karst water flow system in Julongshan syncline were identified by multi-methods such as karst hydrogeological field survey, hydrochemistry and isotope analysis, to find out the hydrogeological conditions of water inrush into the tunnel and select one water diversion scheme with lower risk of karst water disaster.The results show that the aquifer system in Julongshan syncline has a multi-layer structure with an impermeable layer between two aquifers.The Lower Permian is mainly buried underground with weak karst development, while the Upper Triassic bare karst area forms a giant karst basin with multi-stage water flow system.Three tunnel plans were demonstrated in Julongshan syncline area.Plan A passes through the recharge area of the karst water system in the western syncline, in which the length of soluble rock the tunnel passes through is the lowest and all belong to buried karst.It avoids to cross the Triassic karst water basin in the profile, therefore the risk of water-gushing for Plan A is relatively low.However, Plan B and Plan C will cross the Triassic karst water basin with longer soluble rock section and the risk of suffering karst water-gushing is much higher.So, Plan A is recommended.This study can provide a scientific basis for comparison and selection of diversion tunnel line, and also has reference value for similar deep-buried long tunnel construction