Based on the analytical model of a horizontal layered medium, applying the probabilistic formulation, the article presents the results of the investigation of joint work of a structure and multilayer soil bed subjected to seismic loading. The damping properties of soil were taken into account. The authors drew a comparison between the fundamental frequencies of the free vibrations of the “soil - structure” system obtained using the layered medium model and the platform model. By the example of a two-layer soil bed, the dependence of the resonant frequencies of the system on the thickness of the near-surface or buried weak layer was determined.
The results of the analysis of the “two-layer soil - structure” system for seismic loads at various locations of the weak layer were presented. The seismic acceleration of the soil bed was modeled as a stationary random process with a given spectral density. The investigation included an analysis of the amplitude-frequency characteristics, acceleration spectral densities and dynamic coefficients for both the entire system and the individual layers. It was demonstrated that the resonant frequencies of an individual layer being a part of the multilayer system can differ significantly from the resonant frequencies of a homogeneous soil bed with similar dynamic characteristics. A comparison between the dynamic responses of the two-layer soil bed system and a system with the reduced characteristics of the soil bed was drawn at various parameters of the spectral density of seismic load. The intervals of possible values of the resonant frequencies of the system were determined taking into account the random variability of the velocity of transverse waves within each layer.