Investigated is the problem of the influence of bedded rock foundation on the effect of the load transference onto the foundations of massive structures including large dams, power houses, abutments of longspan bridges, silo towers of grain elevators located in seismic areas. The dip of beds of rock foundations of dams in mountain areas can attain high values. The velocity of seismic energy propagation along each of the beds will be depending on the geometry and the physical characteristics of the bed and as a consequence of this the pressure transferred along the dam base will be varying substantially. The effect of dispersion of the waves along the dam base length arises and therewith the motion of various beds turns out to be interrelated and is described with the help of non-linear differential equations.
These equations are solved with the help of electronic computers and a result the domains of unstable motion for the multilayer foundation are found. These unstable motion domains are depending not only on the foundation characteristics but on the parameters of the seismic wave field spectrum, i.e. the domains of the foundation instability for the Particular structure and foundation arise at special interrelations of the wave field parameters. This allows for explanation of a number of emergency conditions occurring in vital structures during the earthquakes. The developed method has b:en used for the numerical computation of the loss of dynamic stability of a rockfill dam of a triangular cross-section, 300 m high, located on a multi-layer rock foundation, the layers dipping at the angle of 45° to the horizontal plane.
The earlier papers of the Authors (Sinitsyn et al. 1987; Sinitsyn et al 1985) published in the Proceedings of the 5th and the 6th Congresses presented the general procedure of the assessment of the seismic stability of massive structure under the action of seismic waves in the near zone of the earthquake. The aim of this paper are the statement and the solution of the problem on the influence of the bedded rock foundation onto the effect of the transfer of load on the foundations of dams and other structures. It has been found from field studies of existing dams that the inclination of the rock foundation beds influences substantially the shape of the diagram of the load transferred on the structure. Inclination of beds of rock foundations in mountainous areas attains great values. For instance, the rock foundation of the Nurek dam is composed of several beds of different thickness dipping at the angle of 45° to the horizontal plane. The flux of the seismic shock energy propagating along each of the beds will have the velocity depending on the geometry and the physical characteristics of the particular bed, and consequently the pressure transferred along the dam base will vary considerably. The effect of the waves dispersion over the dam base length arises (Sinitsyn 1967). the motion of various beds being interrelated And described by nonlinear differential equations.