Design of seepage control system around a large-scale underground powerhouse: A case study of Baihetan Hydropower Station

Abstract

Located at the lower reach of Jinsha River, the Baihetan Hydropower Station is the world’s second largest hydropower station. It consists of a double-curvature arch dam with a maximum height of 289 m and two large-scale underground cavern systems on each side of the bank, which is the largest underground cavern system of hydropower project in the world. The construction site is characteristic of complex geological conditions, and multiple interlayer staggered zones are developed between different strata. Based on the results of on-site packer tests, the interlayer staggered zones generally have a higher hydraulic conductivity than the surrounding rocks, and therefore may act as the potential seepage flow path. Since the underground powerhouse is close to the upstream reservoir and these is a large difference of water level between the upstream and downstream reservoirs, the control of groundwater flow in the surrounding rocks of the underground caverns becomes one of the key technological issues. A large-scale seepage control system including grout curtains and drainage curtains was designed around the underground powerhouses. Besides, the hydraulic conductivity of the interlayer staggered zones was systematically characterized and several anti-seepage tunnels were designed and constructed specifically for the control of seepage flow through the interlayer staggered zones. On this basis, numerical simulation of seepage field was conducted, and the results show that the designed seepage control system is effective in lowering the groundwater level and reducing the amount of seepage around the powerhouse.