The problem of the design and construction of penstocks for hydroelectric stations is practically solved. Thus, steel penstocks are usedfor high-head diversion hydroelectric stations in open stretches (Gizel'don, Baksan, Azma, Khrami, Gyumush, Sukhumi, and Krasnaya Polyna hydroelectric stations). Both steel penstocks (Svistukha, Egorlyk, Perepadnaya-l, Chir-Yurt, Mingechaur, Perepadnaya, Central Farkhad hydroelectric stations) and reinforcedconcrete penstocks (Zemo-Avchal'sk, Dnepr-2, Onda hydroelectric stations) are used for lowand medium-head reservoir hydroelectric stations. In our country there is experience [I] in constructing conduits from in situ concrete with prestressed bars with a diameter of 2.5 and 2.8 m for a head of 55m onthe 15-km-long Northern Donets--Donbas canal, from precast prestressed reinforced-concrete elements with a diameter of 2.8 m for a head of 40 m (0.7 ~an) and from precast elements without prestressing (4.5 km) on the Dnepr--Krivoi Rog canal. Finally, precast prestressed pipes with a diameter of 4 m (3.7 km) are used at the Kuban--Kalaus hydroelectric station.Two designs are used for high-headreservoir hydroelectric stations: eitherthe Conduit with a metal lining is located directly in the body of massive dam (Bratsk, Ust'-llm, Bukhtarma, Toktogul, Boguchany, Mamakan hydroelectic estations) or the concrete-encased conduits extend from the body of the dam to the downstream face (Krasnoyarsk, Sayano-Shushenskoe, Chirkey, Kurpsai hydroelectric stations).When designing the penstocks of pumped-storage stations (PSSs) it is necessary to solve a wide range of new engineering problems. They include first of all the selection of the route of the penstocks with consideration of the engineering-geologic conditions and general layout of the station. As a rule, for the PSSs examined in this article the route of the penstocksruns along a slope composed~soil rather than rock. Traces of landslide phenomena are often found already during surveys. Therefore, when designing penstocks it is necessary to assess the stability of the slope and to develop engineering measures to increase it. Such measures include primarily flattening of the slope, control of the levels and drainage of groundwaters, and grading and stabilizing the slope with construction of a surface water drainage system. The general and decisive conditions for selecting the design of a penstock for the investigated type of PSS are: location of the open route of the penstocks on slopes composed of soils; averageslope of the route of the penstocks 1:6-1:10; the relatively small design head (90-120 m) for PSSs, which for units with an individual capacity of about 20OMWpredetermines the turbine discharge of up to 250 mS/sec and penstock diameter from 6.5 to 8 m.Here it is timely to examine the problem of the reliability of the designs of metal penstocks, on the one hand, and of reinforced-concrete and concrete-encased penstocks, on the other.Despite the fact that among construction materials metal is distinguished by a high homogeneity and ...