Abstract:The Jinping Hydropower Project(Jinping I and II),which is under construction,is located in the Jinping bend of Yalong river,with a total capacity of 8.4×106 kW. Jinping I is characterized by the 305 m high double-curvature arch dam,and Jinping II by the four headrace tunnels which is 17 km long each,with very high pressure and large quantity underground water. The project is scheduled to run in 2012. The Jinping auxiliary tunnels (2×17.5 km) serve as the access tunnels between Jinping I and Jinping II,and also as the exploratory and construction adits for the headrace tunnels of Jinping II. The hydrogeological condition is complicated in the area where Jinping auxiliary tunnels pass through. The technical issues encounted in the construction of the auxiliary tunnels include large quantity and high pressure blowing water,ventilation during the tunnel excavation,and rockburst and the treatment. Since the tunnel construction started in 2003,unexpected large quantity of blowing water with high pressure was encountered and have been controlled. The several cases of large quantity and high pressure gushing water and their characteristics are presented,geological focasting methods adopted in the process of the auxiliary tunnel construction are explained,and the technical route of water treatment is analyzed,and then the treatment measures and suggestions are recommended. The gushing water issue encountered in the Jinping auxiliary tunnels is complicated,and the experiences and methods accumulated during construction could benefit the future construction of the headrace tunnels of Jinping II and some other similar tunnelling projects.