To stabilize the rock foundation for the dam of the Nurek hydroelectric station, grouting operations were called for during construction and operation. Therefore a concrete foundation for the dam core with a system of grouting galleries intended for better coupling of the core to the rock foundation was planned in the canyon part of the river. In addition, two levels of inspection galleries were planned in the dam core. During operation the foundation of the dam core and the grouting galleries are subjected to a hydrostatic head up to 270 m, constant vertical pressure of the weight of the dam of 600 tons/m S , and constant shearing force up to 60 tons/m 2.Preliminary calculations showed that under such a high hydrostatic head with consideration of the allowable seepage gradient the concrete retaining structures of the foundation of the dam core and grouting galleries should have a thickness of 8-10 m. Meeting such a condltlon was not expedient technically or economically. In order to reduce the thickness of the retaining structures of the foundation of the dam core and grouting galleries to acceptable limits it was decided to eliminate seepage through them by using waterproofing. In conformlty with the design standards for severe operating conditions the use of waterproofing of 10-mm-thick stainless steel was required. The total area of waterproofing was 26,540 m 2. For a maximum cost reduction it was decided to replace the steel waterproofing.As a result of analyzing the properties of various waterproof coatings it was established that for this purpose it was most rational to use the epoxy--coal tar waterproofing developed in the research department of the All-Union Planning, Surveying, and Scientific-Research Institute ~Gidroproekt) [1-3], Organic compositions (primer, lacquer, and enamel) on a base of epoxy resins modified by coal tar, the waste from dry distillation of coal, are used as the waterproofing materials in making epoxy--coal tar waterproofing (Table i). A typical design of waterproofing (Fig. I) consists of a coat of primer, three or four coats of lacquer, and a coat of enamel. To increase crack resistance and impermeability to water, the firstthird lacquer coats are reinforced with fiber glass fabric. Reinforcement with fiber glass fabric permits regulating the properties of the epoxy--coal tar waterproofing over a~ide range (Table 2)4 Epoxy--coal tar waterproofing was used successfully for protecting the foundations of six pumping stations along the Karshi canal (total area of coatings 39,500 m2), where it is subjected to the combined effect of compressive and shearing forces, hydrostatic head up to 20 m, and a corrosive sulfate aqueous environment [4]. However, the experience of investigating and using epoxy-coal tar waterproofing did not permit making a well-founded choice of the design of the coating for the severe operating conditions of the Nurek station without additional special investigations. This is explained by the circumstance that the standard and ge~erally acceptedmethods of testing...

Operating experience with flow structt~es of high-head hydrocomplexes indicates that, in regions which are especially susceptible to cavitation, concrete is subjected to intensive disintegration as a result of the cavitational erosion. The cavitation resistance of the concrete may be raised by using high quality filiers and special techniques in preparing and placing the mix,* and in addition, by the requisite protection of the surfaces.At present, expensive metal linings are used for protecting the concrete in such regions, even in temporary structures. Attempts to use gunite, natural stone materiais, wood and resin for these purposes were unsuccessful [1]. Repair of damaged surfaces with portland cement concrete and mortar are time-consuming. Moreover, disintegration sets in again, as it is impossible to achieve a strong bonding of old concrete with new.An analysis of studies of the theory of cavitation permits one to forrnulate the essential properties of a material for protective linings resistant to the action of cavitation. Such a materialmust possess exceptional homogeneity, high elasticity, high density and good dielectric properties. It is practically impossible to select a natural construction material which simultaneousIy satisfies all the requirements set forth.Recently, both abroad and in the USSR, particular consideration is being given to investigating the cavitation resistance of polymer materiais [2-4] whose properties are controlled over an extremely broad range. Plastic concretes were used for repaiz of flow structures of Priest Rapids and Rocky Reach dams, and their successful operation over a period of 4 years permitted the metallic lining installed as a cavitation-resistant protective covering on the submerged spillway of Milford Dam to he replaced by epoxy plastic concrete [5][6][7].In the NIS Gidroproekt (All-Union Planning and Research Institute for Hydraulic Engineering) division of polymer materials, investigations], were made of the use of domestic synthetic resins for preparing cavitation-resistant plastic concretes [8,9]. Specimens were tested for the effect of the cavitation trail arising in a two-dimensional flow behind a cylinder, in both rotary and flow-through testing units and in a cavitation tube [10,11,12]. In the flow-through testing unit the velocity of flow was 33, in the rotary 28, and in the cavitation tube 26.4 m/sec. The corresponding cylinder diameters were 20, 15, and 24 mm. The specimens, on an anchored duraluminum base 10 mm thick measured 35• 70 • 150 mm. Tests were conducted with a degree of hardening of not less than 85% [13].The resistance of plastic concretes to cavitation erosion was evaluated according to loss of weight or volume of the specimens with time, during the action of cavitation, up to that moment when the specific erosion reached a steady magnitude.For selection of the basic cementing agent, tests were conducted on sand plaster concretes with a base of various synthetic resins (Table I). From Fig. I it is seen that plastic concretes with epoxy res...

Protection of the concrete of hydraulic structures against cavitation is quite urgent in the zones of intense hydrodynamic action of a high-speed flow [I_, 2]. One of the proposed ways of solving this problem is by the use of various types of coatings made of polymeric materials, many of which, as domestic and foreign investigations confirm, have a high cavitation resistance [3][4][5].The research department of the All-Union Planning, Surveying, and Scientific Research Institute (Gidroproekt) developed through laboratory investigations various types of cavitation-resistant coatings (paint, mastic, solution) on a base of epoxy resins having high water resistance and mechanical strength, and small shrinkage [6]. However, for the successful use of these types of coatings under field conditions it was necessary to conduct additional investigations and to develop the appropriate technology. The viscosity of epoxy compositions, their viability (time before setting begins), and their setting in the working range, their adhesive strength as a function of various factors, the possibility of applying epoxy coatings to wet concrete, and mechanized methods of preparing and applying variou~ epoxy compositions on a concrete surface were studied.

The stage-II diversion tunnel of the Nurek hydroelectric scheme is designed in conjunction with the stage-I and stage-In tunnels to pass flood flows during construction of the first-phase dams and the hydroelectric station building, and to release irrigation water downstream of the hydropower complex during the reservoir filling and lowering period within the range of levels below the sill of the intake portal of the stage-III diversion tunnel.Depending on the hydrologic conditions the tunnel has had two operating periods: The first was an unregulated period . when it came imo operation with the rise in upstream water level at the commencement of a flood; the velocity of the flow in the tunnel during this period did not exceed 15-16 m/sec. The second was the regulated period , when the head on the gates reached 110 m and the velocity below the gates ranged up to 42 m/sec. To ensure free-flow conditions in the tunnel, the chambe~ housing the regulating gates is provided with an air-supply conduit with a cross-sectional area of 9 m z.With regard to the above-mentioned operating conditions, the lining in the section upstream of the gate chamber, where the tunnel is under press=c and velocities do not exceed 20 m/sec, was designed to be of Mark-200 concrete; in the free-flow section downstream of the gate chamber, where the velocities range from 42 m/sec (at the start) to 32 m/sec (at the end). the lining within the limits of the wetted perimeter is constructed of Mark-400 concrete, with a slump of 2-4 cm for the invert, and the upper part is of Mark-300 concrete. In order to prevent cavitation in the tunnel or keep it to a minimum, strictrequirements were set for the quality of the lining surface (see Table 1).

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