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Experience with the construction of impervious membrane elements on the upstream cofferdam at the Toktogursk hydroelectric plant, a head-producing dam on the Kara Su River , the dam at the Atbashinsk hydroelectric plant (1969)(1970)(1971), and the cofferdam at the Ust'-Khantaisk hydroelectric plant (1970) [1-3] as well as with laboratory work carried out at the B. E. Vedeneev All-Union Scientific-Research Institute of HydrauUc Engineering (VNHG) has indicated the need for developing simple and technically adequate elements, for improving their reliability, for justifying the methods of analysis of such elements, and for determining the durability of the materials used for these elements.

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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.

purpose. To substantiate methods for modeling the earth's surface subsidence in the process of its undermining by stoping in the Western Donbas mines. The methods make it possible to develop the automated system determining areas and volume of the earth's surface flooding to minimize hydroecologic risks while closing down mines in the Western Donbas.methodology. The work substantiates methods to model processes of the earth's surface subsidence helping identify areas of the flooded surface as well as its volume. Therefore, the two types of models (the interpolation model and polynomial one) to con struct surfaces with a regular network have been considered. The models make it possible to get adequate idea of surfaces; more over, they are the basis to calculate volumes, represented in the form of total unit prisms in terms of network node.findings. The developed mathematical and algorithmic apparatus has made it possible to develop effective models of the earth's surface and an aquifer as well as to calculate the zone volumes between the reference earth's surface and the consolidated one as well as between the aquifer to identify the flooded areas.Originality. Methods to model processes of the earth's surface subsidence for hydroecologic risk minimization in the process of mine closing down are substantiated.practical value. The work develops hardware and software to provide efficient modeling of the earth's surface subsidence while mining coal seams and to reduce errors while calculating the immersed surface zone volumes.