Mechanisms of Vertical and Horizontal Seismic Motions on Foundation Liquefaction Response and Uplift of Subway Stations

Abstract

ABSTRACT Historical earthquake-induced damage and studies have shown that the impact of vertical earthquake motions on sand liquefaction cannot be ignored in liquefiable sites with underground structures. Therefore, this study performed a finite element-finite difference (FE-FD) coupling numerical method to compare the influence of different seismic component excitations (vertical, horizontal, and bidirectional) on sand liquefaction with and without subway stations and to further explore the uplift mechanism of the subway station under vertical earthquake motion. The results revealed that the liquefaction response of the foundation soil is much different in the model with and without the subway station. In a liquefiable site with a subway station, the vertical seismic component may also trigger soil liquefaction due to soil structure interaction, while in the unstructured site, it cannot trigger liquefaction. The vertical seismic component will aggravate the degree of liquefaction and horizontal acceleration response of soil near subway stations, and the extent of this influence decreases with the increase of horizontal distance between the soil and the side wall of the subway station. In addition, the influence of vertical earthquake motions on the uplift of subway stations is related to seismic wave characteristics and the value of Arias intensity. The mechanism of the effect of vertical earthquake motion on the uplift of subway stations is to reduce friction between structure and soil and increase the flow deformation of the soil.