No abstract

No abstract

At the present time, the 170 m high Charvak dam and the 300 m high Nurek dam are being constructed by using local materials. The height of the projected dam at the Rogen hydroelectric plant will exceed 300 m. In the foreign hydropower construction practice, the following earthfill dam are wen known: Oroville (USA), 224 m; Bennett (Canada), 183 m; Miboro (Japan), 131 m; and others.

At present a standard evaluation of the seismic stability of earth dams (just as other structures) is performed within the scope of the so-called linear spectral theory of seismic stability [i, 2]. According to this method the actual seismic inertial load is replaced by a certain conventional load determined for each mode of oscillations with consideration of the spectral properties of the structure and is then (when evaluating the stability of the slopes and analyzing the state of stress and strain of the dam) regarded as a static load. Thus the methods include two main stages: determination of the frequencies and modes of free oscillations of the structure and inertial loads corresponding to them; evaluation of the strength and stability of the structure (and its elements) under the effect of the main load combination (dead weight, hydrostatic pressure of water, etc.) and seismic loads.In this case one and the same calculation (linearly elastic) model is usually used for determining the inertial loads and for the static calculation.Such a quasistatic approach has been tested mainly for objects of mass construction (medium-story~buildings on compact soils), and its application by hydraulic structures should take into account the specific characteristics of their behavior.In particular, e.g., such factors as the dynamic interaction of the structure with the foundation, the specific features of the behavior of the material of earth dams characterized by considerable damping, saturation, nonlinear deformability (even in the presence of a relatively low level of stress), etc., should be taken into account.In connection with this the following scheme of evaluating the seismic stability of earth dams within the scope of the standard method seems expedient:The state of stress and strain of the dam from the effect of the main load combination is determined with consideration of nonlinear deformability of the material (and also sequence of construction and loading, yielding of the foundation, etc.); such a calculation can be performed, as is known, e.g., by means of iterations on the basis of available programs for solving the linearly elastic static problem by the finite-element method (FEM) [3][4][5];The distribuion of the deformation characteristics of the structure (and foundation) obtained determines the linearly elastic model used for calculating the frequencies and modes of free oscillations;The calculated inertial loads (together with the main load combination) are used for evaluating the strength and stability of the dam;The actual saturation of the earth of the dam and the dynamic interaction of the structure with the foundation are taken into account approximately at appropriate stages of the calculation. This approach, which does not fall outside the scope of all known conventions of the standard method, permits to some degree taking into account the characteristic features of the behavior of earth dams.Let us examine certain basic stages of the described method for the example of calculating various types of...

No abstract