a sharp change in the levels affects its stress state. Furthermore, the flow of the wells without reliable isolation and disposal of the outpouring water leads to additional wetting of the slope. Filling of the upper reservoir on the level regime of the aquifer [sentence(s) missing in Russian oriKinal] evaluation of their stability.Observations show the rather effective operation of the drainage systems. The exception is the dike of the upper reservoir, where high heads in the horizontal drainage are noted in the part adjacent to the water intake. A decrease of the discharge of the drainage systems and an increase of sanding of the vertical drainage in the moraine are noted simultaneously.An analysis of the data of on-site observations of the deformations on the land-slide slopes of the Zagorsk PSS makes possible routine monitoring of their state.A table of diagnostic characters of the state of the slope in the region of the penstock of the Zagorsk PSS was complied by the time of start of operation of the structure (Table i).During construction of the toe wall, early detection of progressive deformatioss promoted making the correct decision about conducting landslide-control measures and time of trial filling of the upper reservoir.According to the observation data, filling of the reservoir caused an increase of the rate of deformations of the slope up to 0.4 mm/day with a diminishing tendency. Reverse development of this deformation after rapid emptying of the reservoir permitted concluding its "elastic" (pseudoelastic) character (Fig. 3).

During the design and construction of hydraulic structures it is often necessary to estimate the seepage properties of the earth materials of the foundation and abutments, which during surveys are unsaturated. Whereas methods of estimating the seepage properties of saturated soils have been developed to a sufficient degree, for unsaturated materials a number of problems require special investigations. The permeability of unsaturated materials can be estimated by calculation and direct (field) methods, which can be used depending on the required accuracy and reliability of the problems being solved.Calculation Methods of Determining Permeability of Rocks and Soils. The seepage and piping properties of earth masses (rock and soil) are determined by the size, shape, and relative number of water-conducting channels, and also by the characteristics of the physicochemical interaction of solid soil particles with the seepage flow.To solve integral problems in the area of seepage (determination of seepage losses or mean gradients of the head), we can confine ourselves to a homogeneous model, and for estimating the local seepage strength we should use a piecewise homogeneous model. Numerous (direct or indirect) measurements of the water-conductlng channels are used for constructing the piecewlse homogeneous model of an earth mass. The number of channels, being minimum in jointed rock masses, increases in fragmental and reaches a maximum in clay soils. With an increase in the number of channels the effect on permeability of their shape and also orientation relative to the boundaries of the mass decreases. This makes it possible for each variety of earth masses to establish the most important characteristic determining the seepage and piping properties with consideration of secondary characteristics in the form of correction factors.Seepage ~n rocks was investigated by Lomize, Ratz, Chernyshev, Ivanova, Nasberg, and others. As a result of these investigations, regularities of the flow of water in single, equally rough joints were established, which are described by a family of gradlent-veloclty characteristics in a wide range of variation of velocities and gradients (Fig. i). An important feature of these regularities is the transition of a laminar flow regime to a turbulent regime, whereupon condition (I) is fulfilled for the laminar regime and condition (2) for the turbulent regime: is/g~]ug;where iZ, it, uz, u t are the gradients and velocity of the flow in a Joint, respectively, for the laminar and turbulent seepage flow regimes; g, acceleration of gravity; ~, open width of the joints (the average distance between its walls); v, kinematic viscosity coefficient of water; A and B, roughness parameters determined experimentally.The equation of the critical line demarcating the flow regimes has the form S --4 uc= 7where u c and uiare respectively the critical velocity and gradients of the flow.

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...