Keywords: earth dams, non-linear, moisturing, elastic-plastic characteristics, bi-linear diagram, accelerograms of earthquakes.

In assessment of the stress-strain state (SSS) and dynamic behavior of earth structures existing methods and algorithms do not take into account a number of factors, such as: the structural features of earth structure and the occurrence of the real characteristics of soil materials. In this paper these factors were considered within the limits of variation of the mathematical statement of the problem and the finite element method.. Under the static loads acting on the structure the discussed variational problem accounting for elastic-plastic and non-linear-moisturing soil properties of is solved using the finite element method reducing to the solution of non-linear systems of equations. The non-linear algebraic equation within each step of the iteration is solved using Gauss' method; the non-linear differential equation with initial conditions for each step of the iteration is solved using Newmark's step-by-step method.

With these algorithms the SSS and the dynamic behaviour of three earth dams of different height and under different loads were evaluated. The main conclusions of the paper are:

1. Under static loads the influence of the elastic-plastic characteristics of soil on the SSS of a dam is increases with the height of the dam. In the kernel of a dam vertical stresses and the intensity of stresses become less and an arc effect is strengthening. The growth of moisture content leads to a drop in the intensity of stresses and to the growth of horizontal stresses in the lower part near the foundation; that may lead to a decrease of the resistance of the structure to shear; an increase in tangent stresses in the kernel and near upper slope may lead to formation of cracks and the occurrence of land-slides.
2. Under dynamic effects it was revealed that the SSS of the structure is influenced not only by the maximal value of acceleration, but mainly by the frequency spectrum and the duration of the effects. Here the strengthening of the arc effect in the zone of a kernel, that is typical for vertical stresses, is the result of different deformation characteristics and the yield limits of the soils of the kernel and prism. With an increase of the water content of the soil, the intensity of stresses in a kernel becomes less. It should be stated that in the resonance mode it is half compared with the kernel of a dry soil. Such a quick change of intensity of stresses in the zone of a kernel may lead to the appearance of cracks both in transient zones and in the kernel itself. To obtain the real character of the SSS of high dams under forced vibration it is necessary to account for the elastic-plastic characteristics and the moisture content of soil.

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