Underground structures may be buried in liquefiable sites, which can cause complex seismic response mechanisms depending on the extent and location of the liquefiable soil layer. This study investigates the seismic response of multi-story underground structures in sites with varying distributions of liquified soil employing an advanced three-dimensional nonlinear finite element model. The results indicate that the extent and location of liquefied soil layers affect the seismic response characteristics of underground structures and the distribution of their damage. When the lower story of the subway station is buried in liquefied interlayer site, the structure experiences the most serious damage. When the structure is located within a liquefiable interlayer site, the earthquake ground motion will induce greater inter-story deformation in the structure, resulting in larger structural residual displacement. When all or part of the underground structure is buried in the liquefiable soil layer, the structural failure mode should be assessed to ensure that the underground rail transit can quickly restore functionality after an earthquake. Meanwhile, permeability effects of liquefiable soil have a significant impact on the dynamic response of subway station in the liquefiable site.

Under strong earthquakes, subway station structures situated in potentially liquefiable soils may experience complex seismic response scheme when the structure base slab is embedded in non-liquefiable soils while the sidewalls and top slab are buried in liquefiable soils (hereinafter referred to as a liquefiable sites). This paper investigates the dynamic seismic responses of multi-story underground structures in liquefiable sites employing an advanced three-dimensional nonlinear finite element model. The results indicate that the seismic response of underground structures is primarily determined by the soil displacement and the soil-structure stiffness ratio. In addition, the seismic response of the soil-underground structure system is strongly influenced by the distinct characteristics of the input ground motion. Seismic input motions rich in low-frequency components are more likely to cause saturated sand layers to liquefy and are likely to trigger more pronounced flow deformations, leading to severe damage to underground structures. Generally, liquefied soils are prone to significant horizontal displacements (i.e., lateral spreading); however, due to the reduced soil-structure stiffness ratio, the soil ability to induce shear deformation in the structure is diminished, and hence the structure does not undergo large horizontal deformations same as that of the soil. Additionally, structures may exhibit a slight tendency to uplift after the earthquake. These observations can inform the seismic design of underground structures in liquefiable sites.