Some problems with the use of film materials for facing hydraulic structures

Abstract

During the past two decades the use of watertight polymer film facings have found wide use in the construction of earth structures. The number of earth structures with film facings (excluding canals) constructed in the USSR in 1959-1976 has trended upward (see Fig. i).Of the 65 structures that we considered, there were 6 dams and cofferdams at hydropower developments, 5 sludge storage ponds and ash dumps for central heating and power plants, 5 dams of industrial structures and quarries, 20 reservoirs for agricultural and water-supply use, and 29 tanks for storing harmful wastes from chemical plants.Among the structures with watertight films we need note first of all the dam of the Atbashin hydroelectric station with a film diaphragm designed for a head of 36.5 m and the Toktogul reservoir with a surface area of 657 ha and depths to 31m, which is completely faced with polyethylene film. The geographic location of structures with film facings is rather wide: Yakutsk ASSR, ~gadan Oblast, Kola Peninsula, cities of N0rilsk and Vorkuta, Central Asia, Armenian SSR, Leningrad 0blast. The greatest number of structures with film facings have been constructed in the Leningrad Oblast (5), in Central Asia (ii), and in the Armenian SSR (11).Film facings and diaphragms are in essence a fundamentally new type of watertight cons=ruction, the progressive character of which is determined first, by the strictly functional character of the structural elements (the film provides only watertightness and cannot participate in the static work of the structure, the purpose of protective layers is to protect the facing from mechanical damage and the purpose of the revetment on the upstream slope is to guard the protective layers from wave destruction and random effects) and second, by the insignificant volume of the impervious polymer element itself (its centralized manufacture and delivery to any region of the Soviet Union is possible). Such properties of watertight films effect a decrease in the cost of the structure, a decrease in labor costs, a simplification of construction technology, and often an overall reduction of construction time. It is significant that a considerable reduction in the thickness of impervious elements predetermines the effectiveness of their use under practically all climatic and geological conditions in the original and economic engineering decisions.Film facings provide also operating reliability of the structures and increased quality of construction. According to data by D. Scott (USA) film facings reduce seepage losses by 98% on the average, whereas bituminous facings reduce them by only 36-78%. Czech specialists give analogous data in their reports. The results of the experimental work of V. V. Sokol'skaya indicate a 92-96% decrease in water losses from film-faced canals.