# Influence Analysis of Liquefiable Interlayer on Seismic Response of Underground Station Structure
## 4 Dynamic Response Analysis of Station Structure
### Influence of the Relative Density of the Liquiditable Interlayer  
Relative density has an important influence in triggering sand liquefaction. In this section, the most unfavorable case (case b) of the liquifiable interlayer crossing the station structure analyzed in the previous section is used as the base case, and the relative position and thickness of the liquifiable interlayer are kept constant to further investigate the effect of the variation in the relative density of the sand interlayer on the dynamic response of the station structure. Figure 10 shows the acceleration amplification effect of the station structure plate and column. On the whole, the acceleration response of the station structure at different heights differs under the seismic effect, and the peak acceleration of the plate structure is much lower than the peak acceleration of the column structure. The lower the relative density of the sand interlayer is, the stronger the acceleration amplification effect inside the structure will be. The acceleration response at the top and bottom plates of the structure is less affected by the relative density, while the acceleration of the middle plate and the middle column structure is strongly affected by the change in the relative density of the sand interlayer. It is worth noting that the maximum acceleration amplification coefficient of the column structure on the upper level of the station reaches 6.45 in case d. The reason  
Figure 8: Influence of the spatial position distribution of the liquifiable interlayer on the relative displacement of the top and bottom plates of the station structure. Figure 9: Influence of the spatial position distribution of the liquifiable interlayer on the shear stress at each section position. for this is that the great liquefaction of the sandwich soil leads to the weakening of the restraint effect of the soil on the structure, which results in greater differential acceleration inside the structure [31,32]. Figure 11 shows the maximum horizontal relative displacement curves of the station side walls under different relative densities of the interlayer. From the figure, it can be seen that the horizontal relative displacement of the structure, with a 70% relative density of the interlayer, is the lowest in case e. As the relative density of the sand interlayer decreases, the degree of liquefaction gradually increases, and the horizontal deformation of the station structure side wall also gradually increases. The maximum relative displacement between the top and bottom plates is 33.4 mm in case d, which increases by 29.4% compared with case e.  
Figure 12 shows the maximum shear stress at each measured point of the station structure under different relative densities of the liquifiable interlayer. From the figure, it can be seen that the maximum shear stress magnitude at each key section of the wall and column decreases with the increase in the relative density of the sand interlayer, but  
Figure 11: Influence of the relative density of the liquifiable interlayer on the horizontal relative displacement of the side wall. Figure 10: Acceleration amplification effect of the station plate and column structure. the degree of reduction varies between different section locations. The shear stress at the bottom of the station structure is less affected by the relative density. The shear stress at the connection between the side wall and the middle plate decreases most significantly with the increase in the relative density and is most affected by the degree of liquefaction of the sand interlayer, which should be given more consideration in seismic design. Figure 13 shows the time course curve of the soil and water compressive stress in the middle of the side-wall-monitoring element S. It can be seen that the development trend of the soil and water compressive stress is similar in each case, always progressing through the three stages of \"smooth development, fluctuating rise and stabilization\".