Seismic wave propagation in layered liquefiable soils

Abstract

Many past earthquakes with the magnitude close to 7.0 (Mw) or more have shown liquefaction phenomenon. Often liquefiable deposits occur in layers. Seismic waves travelling from bedrock are modified by the presence of layered soil, where seismic impedance contrast is seen as the reason. Recent studies have shown that the presence of a liquefiable soil layer can significantly reduce inertial load on the superstructure, i.e. liquefaction of soil layer prevents the transmission of seismic waves (mainly shear waves) acting as shield protecting the above layers (base isolation effect). However, many studies are limited to only two-layered soil, where a liquefiable soil layer is present above a non-liquefiable soil layer. However, in the field, there could be situations with multiple soil layers and a liquefiable layer could be present as a sandwiched layer between non-liquefiable layers. The seismic site response study considering the effect of layering in the soil deposits for liquefiable sites is least considered while carrying out foundation design. In the present study, two soil profiles (a sandwiched liquefiable layer and a sandwiched non-liquefiable layer) were studied by varying the thickness of each soil layer. The soil profiles were subjected to a typical ground motionfrom 1995 Kobe earthquake. The effect of layered liquefiable deposits on the seismic response of the ground is studied. The results, such as attenuation of acceleration, displacement and the spectral acceleration, were studied in detail and presented in this paper.