Excavation and Backfilling of a Large Temporary Bottom Outlet through Baglihar Concrete Dam under Reservoir Water Pressure

摘要

In this paper the excavation, closing and backfilling of a large temporary bottom outlet under water pressure through the then partially completed Baglihar concrete gravity dam in India is reported. The bottom outlet was used as a last resort to create a river diversion after both diversion tunnels were entirely blocked by landslides, and inundated with reservoir water. The 6.8m diameter bottom outlet is reported to be the largest passage ever to be driven through an existing concrete dam. Both the opening and closing of the passage below water level provided several challenges, and the technical details of its excavation, blasting, closing and backfilling are recorded. Moreover, a brief summary of similar works are provided. The experience collected from this challenging work may become useful not only for dam builders but also for tunnelling engineers.