Achievements and New Considerations on Reconstructing of Diversion Tunnel into Spillway Tunnel in High Earth and Rockfilled Dams

摘要

There has been more than half century on the reutilization of diversion tunnel in the world.Most of them are reconstructed into the permanent spillway tunnel or low outlet,such as the Shuibuya CFRD (233 m),Tianshengqiao I CFRD (178 m),Zipingpu CFRD (159 m),Xiaolangdi Rockfill Dam (154m),Mica Rockfill Dam (240 m),Gongboxia CFRD (132 m) and so on. The water heads of spillway tunnel in those dams are generally over 100 m and discharge capacities over 1000 m3/s. This kind of design makes the Layout of the project more compacted,reasonable and cost saving. As the more and more attention on eco-environmental protection has been paid in the project design,the environmental flow has to be released during the initial water pounding period of the reservoir by a tunnel or outlet,especially on the high earthfill or rockfill dam project. The lesson from Zipingpu CFRD in china "5.12" Earthquake in 2008 indicates that one or two low outlet is necessary and very important on the dam safety management when there is earthquake happened. The paper will discuss the necessity,technical possibility and key aspects on the re-construction of diversion tunnel by considering the issues of eco-environmental protection and dam aseismic safety.