# Influence Analysis of Liquefiable Interlayer on Seismic Response of Underground Station Structure
## 4 Dynamic Response Analysis of Station Structure  
### Influence of the Relative Position of the Liquifiable Interlayer  
Element A, in the middle of the top plate of the structure, was monitored, and the acceleration time course in each case was obtained as shown in Figure 7. It can be seen that the relative position of the Liquifiable Interlayer is not affected by the change in the relative position of the Liqu  
Figure 6: Distribution cloud map of excess pore pressure ratio of liquefied interlayer after the end of the earthquake in different conditions: (**a**) case a (\(H=5\) m, \(D_{\rm r}=50\%\)), (**b**) case b (\(H=5\) m, \(D_{\rm r}=50\%\)), (**c**) case c (\(H=5\) m, \(D_{\rm r}=50\%\)), (**d**) case d (\(H=5\) m, \(D_{\rm r}=30\%\)), (**e**) case e (\(H=5\) m, \(D_{\rm r}=70\%\)), (**f**) case f (\(H=12\) m, \(D_{\rm r}=50\%\)), (**g**) case g (\(H=20\) m, \(D_{\rm r}=50\%\)).  
from the figure that the peak acceleration of the top plate of the station is the greatest when the liquifiable interlayer is located on both sides of the station (case b). When the liquifiable interlayer is located at the bottom of the station structure (case c), the peak acceleration of the structure is the lowest, because the soil under the structure is liquefied under the seismic load, and the soil loses its shear characteristics and hinders the transmission of shear waves. Accordingly, the disturbance of the upper metro station is greatly reduced. This indicates that when the liquifiable interlayer is distributed in the lower area of the station, it has a certain seismic isolation effect on the station structure.  
The time course curves of the relative horizontal displacement of the top and bottom of the structure when the liquifiable interlayer is located in different spatial positions are given in Figure 8. As can be seen in the figure, the peak relative displacement at the top and bottom of the structure is greatly influenced by the distribution of the liquifiable interlayer location. The peak relative displacement of the structure is the greatest in case b, where the liquifiable interlayer crosses the side wall of the station structure, and the maximum relative displacement is 28.08 mm. Meanwhile, in case c, when the liquifiable interlayer is located at the bottom of the structure, the peak relative displacement is only 12.12 mm, which is reduced by 56.8% compared with case b. From the point of view of structural seismic resistance, when the liquifiable interlayer is located in the lateral foundation of the station structure, the lateral deformation of the structure is the greatest, and it is more likely to be damaged under the earthquake action.  
The underground structure is constrained by the surrounding soil layer and mainly undergoes shear deformation under the action of the earthquake. To further investigate the influence of the degree of liquefaction of the interlayer on the structural forces, stress monitoring was conducted, focusing on the key parts of the wall-column structure, and the maximum shear stress at each monitoring point of the structure was obtained as shown in Figure 9. After comparison, it can be seen that the shear stresses at various parts of the structure are higher when the liquifiable interlayer crosses the side wall of the structure (case b), and the shear stresses at the W2 section of the side wall are especially prominent. When the liquifiable interlayer is located at the bottom of the structure (case c), the magnitude of the shear stresses at all parts of the structure is reduced, which also proves that the interlayer has a certain seismic isolation effect when it is located at the bottom of the structure from the perspective of force.  
Figure 7: Time course curves of station roof acceleration under different spatial location distribution conditions of the liquefaction sandwich.