The Rogun hydro project [i] --a multipurpose irrigation and power facility --is the uppermost s=age of the Bakhsh network and is located 70 km upstream from the Nurek hydroelectric plant.The plant's rated capacity for six units is 3,600,000 kW, its average annual generation of electric power is 13 billion kwh, and the full and useful volumes of its reservoir are 13.3 and 8.6 km s, respectively.In geologic respects, the segment containing the site is a single tectonic block bounded by the second-order Ionakhsh and Gullzindansk fractures and the deep flrst-order Vakhsh fracture. The section is subject to nlne-polnt earthquakes.The bedrocks --Lower Cretaceous sandstones, siltstones, and argillltes--beyond the weathered zone are distinguished by hlgh-strength properties, regardless of the appurtenances to this or any other blocks; in the saturated state, the average compressive strength under a unlaxially applied load reaches 105 MPa for the sandstones, and 60 MPa for the siltstones and argillites.The entlre mass in the vertical profile is divided into four zones according to its physicochemlcal and seepage properties as a function of embedment depth and the extent of the effect of weathering and unloading processes on the rock mass: I --zone of severe weathering and unloading; If--zone of weathering and unloading; Ill--zone of unloading; and IV --zone of virtually unchanged rock.The following comprise the Rogun hydro project (Fig. 1): structures of a steady-head facility with an underground powerhouse and open distribution device, construction tunnels, and an underground-type operational sluice, a structure for protecting the salt stratum from scour in the foundation bed of the dam, structures to protect the agricultural complex on the Obi-Shur dry bed, and service tunnels.The structures of the underground complex, whose overall length of excavation reaches 60 km, occupy a speclal place in the design of the Rogun plant~ In designing the underground structures for the plant, we encountered many problems caused by the unique parameters of the structures, and by the complex natural conditions of a portion of the construction. To resolve these problems, we conducted the necessary designresearch work, which resulted in new progressive solutions that produced a positive effect expressed as the technical feasibility of the problem solution, savings in construction materials and labor outlays, a reduction in construction costs and time, improvement in the operational reliability of the structures, etc.Construction Tunnels. The use of gates that operate under heads of up to 200 m in the construction Gunnels makes it possible to discharge from one tube (third stage) of the construction tunnel.Routing of the construction tunnels from the left to right bank along the shortest path with a transition to reinforced-concrete pipes through the river channel, and also the combination of these tunnels with the plant's discharge tunnels (Fig. 2) made it possible to reduce the overall length of both tunnels by 1500 m. With this routing,...
