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The suggested method of model computation can be used for developing criteria of seepage safety.Operation of hydrotechnical structures situated in a city is connected with enhanced risk, because in this case emergencies can have very negative consequences. The federal law "On Safety of Hydrotechnical Structures" adopted in 1999 stipulates periodic inspection of such structures and issuing of a declaration that guarantees the requisite level of their safety. If this is not done, the operation of the object can be suspended until the necessary measures on repair or updating are taken.In the present work we consider a possible succession of assignment of hydrogeological safety criteria and the initial data required for the purpose. As an example we present materials reflecting the appearance and development of an emergency situation at the Skhodnenskaya HPP (in Moscow) in January -April 2003.The hydropower plant in question was built in 1938 within the Moscow-Volgostroi Project and operates in a variable mode. The waterworks facility includes a headrace diversion channel, a gravity reservoir, two pressure pipelines 5.4 m in diameter and 181 m in length each, a power house, and a tail race. The pipeline lies in an excavated natural slope of the left flange of the valley of the Skhodnya River on supports fabricated from reinforced concrete and directly adjoins the power house.The studied geological section was represented from bottom to top by Kimeridgian clays of the upper crust (J 3 km) with a thickness of 10 -12 m, upper Jurassic clays of the lower Volga substage (J 3 v 1 ) with a thickness of 8 -9 m, fine and dusty sands (J 3 v 2 ) with a thickness of 7.5 m, lower Cretaceous fine and dusty sands (K1 nc) with a thickness of 4 -5 m bearing sandstone intercalations, fine and dusty sands of the water-glacial origin (f, lgQ II ) with a thickness of 3.5 -4 m, and sand clays and loams of the Moscow moraine (g, Q II ms) with a thickness of up to 2 m.Most of the sediments bear water. The sandy and sandy loam ground confines a water-bearing ascending-descending complex formed on upper Jurassic poorly permeable parent material. The water-bearing complex has undergone considerable technogenic changes during the construction and operation of the waterworks facility. The level regime of the subsurface water is controlled by a system of drains and by a sheet-pile curtain (Fig. 1).An ancient stabilized landslip covers a major part of the section considered in the lower part of the slope over the route of the pressure conduit. The slip has a block structure. The displaced or deformed lower Volga and Kimeridgian argillaceous sediments are combined in a bottom slip block dpQ III (J 2 km + J 3 v 1 ). The roof sand strata are treated as a single member described as a top slip block dpQ III (f, lgQ II , K 1 nc + J 3 v 2 ). The formation of this block is connected with the processes of passive displacement of the sand stratum down the slope during the development of the slip and partially with the processes of collapsing and slope washo...

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.

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