Slope stability at the zagorsk pumped-storage station: Lessons in surveying, design, and construction

Abstract

An analysis of the experience gained in constructing the Zagorsk pumped-storage station (PSS) is important for constructing other pumped-storage stations in the European part of the USSR. They are especially valuable for structures being constructed on moraine soils. We will trace the course of investigations and change in the notions about the stability of the slopes in the stretch of the Zagorsk PSS at various stages of design and construction. This matter has fundamental importance for pumped-storage stations and became especially acute at the object under consideration.The stretch of the PSS is located north of Zagorsk, in the valley of the Kun'ya River, a left tributary of the Dubna River, belonging to the Volga basin. The selected site is confined to the northwestern slope of the Klinsko-Dmitrovskaya Ridge. The latter has relative elevations of 50-70 m and represents terminal moraine forms of Moscovian glaciation (Fig. i).When assessing the selection of the site of the PSS it is necessary to bear in mind the following. The construction site was selected on the basis of the conditions of the relief providing a sufficient difference of heights between the upper and lower reservoirs, amounting to I00 m. At the same time, the confinement of the high relief to complexly structured glacial formations inheriting, apparently, the more ancient deep geological structure predetermined the characteristics of the conditions of the stretch. The need to choose between maximum elevations and a simpler geological structure is inevitable when siting a PSS under flatland conditions. Therefore, from an engineering-geological viewpoint pumped-storage stations should be referred to especially complex objects. This conclusion is completely confirmed by the experience of surveying and constructing the Zagorsk PSS.However, experience is gained with time. Its lack and failure to take into account the possibility of complications related to the general state of engineering-geological knowledge about certain characteristics of glacial formations were felt at the first stages of surveying and design.The original evaluation of the engineering-geological conditions of the selected site was favorable. It was based on general geological premises, the main one of which was that the construction area is characterized by the continuous distribution of glacial deposits of great thickness. This made it possible to site the structures on moraine soils.By this time (end of the 1950s) a certain stereotype had taken form with respect to an evaluation of a moraine as the foundation of structures. It was based on a study of the properties of moraine soils having high strength and deformation indices, which was established by numerous laboratory investigations and in a number of cases was confirmed by the experience of constructing low-head dams, locks, and canals. The available data indicated invariably good qualities of a moraine, thanks to which notions about it as favorable and reliable soil were firmly established among engineering geologists and...