# Influence Analysis of Liquefiable Interlayer on Seismic Response of Underground Station Structure
## 4 Dynamic Response Analysis of Station Structure
### Influence of the Layer Thickness of the Liquifiable Interlayer  
The analysis in this section, again, takes case b as the benchmark case, keeps the relative position and relative density of the liquifiable interlayer unchanged, gradually increases the thickness of the sand layer, and further explores the influence of the thickness change in the liquifiable interlayer on the dynamic response of the station structure. Figure 14 shows the maximum horizontal displacement curve of the side wall of the station under different layer thicknesses of the liquifiable interlayer. It can be seen from the figure that when the whole liquifiable interlayer is only distributed in the lateral foundation of the structure (case b and case f), as the thickness of the interlayer increases, the horizontal relative displacement amplitude of the side walls gradually increases, and the lateral deformation of the structure also increases. When the thickness of the liquifiable layer is 12 m (case f), the relative displacement between the top and bottom of the structure is the greatest, reaching 46.6 mm, which is 1.6 times that of the site where the interlayer thickness is 5 m. In case g, when the thickness of the liquifiable layer is 20 m, the station structure is completely placed in the liquefiable interlayer, and the relative displacement of the side wall of the structure is the lowest, only 26.5 mm. Under earthquake action, the water and soil pressure produced by the liquefiable sand interlayer on the structure is greater than that of the non-liquefiable clay layer. As the thickness of the liquefiable layer increases, the contact area between the side wall of the station and the liquefiable interlayer increases, further increasing the lateral deformation of the structure; When the structure is completely placed in the liquefiable layer, the water and soil pressure difference on the structure is greatly reduced, so the deformation of the structure is minimal. The shear stresses in each key part of the structure under different thicknesses of liquefaction interlayer are shown in Figure 15. From the figure, it can be seen that when all the liquifiable interlayer is only located in the lateral foundation of the structure (case b and case f), the influence law of the liquifiable layer thickness on each part of the station structure is not consistent. The variation of liquifiable interlayer thickness does not have much effect on the magnitude of shear stress in each section of the central column, the shear stress at the intersection of the structural side wall and the top and bottom plate gradually increases with the increase in the interlayer thickness, but the magnitude of the shear stress at the connection between the side wall and the central plate gradually decreases. When the thickness of the liquifiable interlayer is as great as 20 m (case g), the amplitude of the shear stress in all parts of the station wall and column structure is the lowest, being much  
Figure 14: Influence of layer thickness of liquifiable interlayer on horizontal relative displacement of side wall. lower than in other cases. The reason for this phenomenon is that the soil in the lower part of the structure liquefies first, and the soil near the sides of the side walls flows downward, which slows down the effect on the horizontal shear of the structure. The research of [PERSON] et al. [33] showed that the thickness of the liquifiable soil layer is one of the key factors affecting the uplift of underground structures. Firstly, the developmental trend of the vertical displacement of the structure is analyzed. Taking case b as an example, it can be seen from Figure 16 that the structure gradually starts to float within 0-4 s, and the floating amplitude is almost negligible. With the increase in seismic intensity, the vertical displacement of each monitoring point climbs rapidly for around 4 s and then reaches the peak and fluctuates; at the end of the seismic action, the vertical displacement tends to become stable and remains basically unchanged.