Epoxy-coal tar waterproofing of structures at the Nurek hydroelectric station

Abstract

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...

Experience with the use and operation of epoxy-coal tar waterproofing

“…No damages of the waterproofIng are observed. Inspections of the rooms in the waterproofed structures did not reveal leaks [8].…”