Simulation of spatially variable seismic underground motions in saturated double-phase media with overlying water excited by SV-wave and difference from P-wave incidence

Abstract

The spatial seismic excitations affected by water-saturated soil, a double-phase medium, and overlying water are desirable to be considered for evaluating the seismic response of some typical structures such as large-span cross-sea bridges considering soil-structure interaction. This paper focuses on the study of a theoretical method and numerical simulation of multi-support seismic underground excitations in saturated soil with overlying water for obliquely incident SV waves that can produce P1, P2 and SV waves in saturated soil. First, the reflection coefficients (results are different from the case for P waves incidence) of three kinds of waves (P1, P2, SV) at the interface between saturated soil and overlying water are derived. Based on the reflection coefficients and the boundary conditions at the elastic solid-saturated soil interface, the transfer functions of soil layers with arbitrary depths are proposed to calculate the key elements (i.e., the underground power spectral density, response spectrum function and underground coherency function) for generating the multi-support seismic underground motions. Second, these three key elements are used to establish the underground power spectral matrix, and then the underground motions are generated by decomposing the matrix. Finally, the method is verified by numerical examples and the influences of overlying water depth and incident angle on ground motions are investigated. The effect of incident angle on transfer functions show great difference between the small-angle and large-angle case. Moreover, the phenomenon that is diffrent from P-waves incidence case is investigated,found and emphasized, and the reasons are given.