Rogun dam is a 335 m high clay core rockfill dam, which will be constructed on Vakhsh River in Tajikistan. Originally, two diversion tunnels with similar geometry were designed for discharging the seasonal floods, up to 3290 m3/s. River diversion was carried out in November 1987 and a 45 m high rockfill cofferdam was constructed. However, because of two collapses in the diversion tunnels, the cofferdam was overtopped in May 1993. Reconstruction of these tunnels started in 2009 and the collapsed areas were repaired. Nowadays, the design of complementary rehabilitation including new concrete lining for those parts of the tunnels, which will be used as tailrace tunnels are underway. The present paper describes the present conditions of diversion tunnels No. 1 & 2 and explains the procedure used for stress analyses of tailrace tunnel No. 1 without and with the new lining, which, has been designed to guarantee its long-term performance.
Rogun dam is a rockfill dam with clay core, which will be constructed on Vakhsh River in the Republic of Tajikistan. In its final stage, with crest elevation of 1300 masl, it will be 335 m high and therefore, the highest dam in the world under construction. The powerhouse is of underground type and with its 6 turbines it will have total capacity of 3200 MW. Originally, two diversion tunnels with similar geometrical characteristics were designed for discharging the seasonal floods during construction period of the project, up to 3290 m3/s. Each tunnel is of D shape section with various sizes along its length, starting with 11(w)x11(h) m in pressurized section which reaches to a gate chamber and after the radial gates, there is a sloping part with 14(w)x11.9(h) m section. Finally, cross section of the tunnel converts to 14(w)x17(h) m which will be used as tailrace tunnel during operation period. Each tunnel is almost 1410 m long and while its inlet portal and almost 950 m of its length is located at left bank, after crossing the river, its outlet portal is situated in right bank. The total length of each tunnel is about 1410 m. Construction of the project started in 1980's during which excavation and construction of the two diversion tunnels were carried out. River diversion was carried out in November 1987 followed by construction of a 45 m high rockfill cofferdam. However, because of two main collapses in the diversion tunnels the cofferdam was overtopped in May 1993. Reconstruction of these tunnels started in 2009 and the collapsed areas were repaired. Nowadays, the design studies of complementary rehabilitation works including new concrete lining for those parts of the tunnels, which will be used as tailrace tunnels are underway. This paper describes the present conditions of diversion tunnels No. 1 & 2 and explains the procedure used for stress analyses of tailrace tunnel No. 1 under the highest overburden without and with the new lining, which, has been designed to guarantee its long-term performance.
