Study on the characteristics of karst water system and tunnel route selection in Wanshoushan area, Yunnan Province

During construction of tunnels in karst areas， geologic hazards， such as water bursting and mud invasion， often occur threatening the project and people’ safety. Thus the optimization of tunnel line is very important. Taking the Wanshoushan tunnel of the Sanqing expressway in Yunnan as an example， this work conducted a large-scale hydrogeological survey around the tunnel site. The purpose was to clarify the spatial distribution of the karst water system and cycle features of karst underground water， study the relationship between the different tunnel schemes and spatial position of the karst water system， and predict possible karst water hazards related with these schemes. On the basis of this research， the quantitative assessment indexes for comparison of tunnel line schemes were determined， which were the number of faults running through by the tunnel， the karst aquifer length through which the tunnel extends， maximum water bursting pressure and maximum amount of water invasion. Then using the analytic hierarchy process method，we established a comprehensive assessment model for the tunnel line in the karst area， which would help choose the best scheme of the tunnel line from candidates. The results show that the scheme C possesses relatively better hydrogeological conditions and least risk of karst water bursting or mud invasion.