The diversion runnel, located on the left bank of the Sulak River and intended for diverging the river from the canyon where the Chirkey Hydroelectric Station is being constructed, is one of the large underground structures composing the hydro development. The diversion runnel" was constructed in 1985-1988 with the use of technology and mechanization of work corresponding to the modern progressive level of tunnel construction.Tunnel Characteristics. The free-flow tunnel ( Fig. 1), 729.6 m long with a cross sectional area of 130 m ~-, is designed for a discharge of 1550 mS/sec at a 50 frequency and a check discharge of 2200 mS/sec with 1(70 frequency. The maximum flow depth in the tunnel is 10re.and the velocity a t the tunnel outlet is 19 m/see. The.tunnel passes through laminated and thin-laminated limestones, and only in the stretch of the exit portal does it intersect marly limestones. In the middle of the route the runnel intersects a block of limestones containing several interlayers of clay with a maximum thickness of 10 cm. The Protod'yakonov strength coefficient of the limestones is f =4-11. Along The tunneI route were found groups of rocks characterized by a certain position of tectonic jointing relative to the tunnel axis, degree of rock weathering, and strength parameters. Based on these rock group% four typ~ of reinforced-concrete lining were adopted on the basis of static calculations, which differed in the amount of reinforcement but had a constant Thickness of 80 cm (Table 1).

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