FUSE SHELL: AN INNOVATION FOR COPING WITH UNCERTAINTIES IN DAM ENGINEERING

In View of water crisis in the world and economic considerations, impoundment of reservoirs during construction can be very important especially for large dams in developing countries. Using seasonal characteristics and forecasting models the first filling can be achieved after the flood season. But the spillway should be in service before the next flood season. In the course of a research on early impoundment of 165-m high Marun dam in Iran, an innovation appeared that would enhance the safety and flexibility of the first impoundment which is the most dangerous period in the life cycle of a dam. A thin concrete shell was proposed for plugging of diversion tunnel, which could readily be exploded if required to reverse the impoundment. The concrete shell was appropriately called fuse shell. The fuse shell would enhance the flexibility of the design especially in view of common uncertainties of water engineering. Unfortunately the fuse shell idea was not implemented for the first filling of Marun dam in March 1996. So when unexpected leakage of more then 7 m3/s occurred during the filling, the 10-m long concrete plug lacked the desired flexibility. The fuse shell could have saved the day. It could have ended the crisis in 2 or 3 days instead of 6 months. The probability of piping in the core, the delay in construction activities and the environmental damages to the fishes after the explosion of the gates could have been avoided. In practice, the first application of the fuse shell was in another Iranian dam, Godalandar on Karun River for the first impoundment in Dec. 2000. Unlike the Marun project, there was no need for explosion of the plug in the first impoundment of the Godalandar dam in December 2000. However, the existence of the fuse shell gave the owner and the consultants the assurance required for a safe and flexible impounding scheme.