# Seismic Response and Mitigation Analysis of a Subway Station in the Site with Weak Interlayers
## 2 Seismic Response of the Subway Station in the Site with Weak Interlayers
### Computational Result  
Under seismic loading, significant lateral displacement of the station's sidewall is a critical factor in the structural damage of the station. Simultaneously, damage to the station's central column often precedes that of the sidewall. The extraction of horizontal displacements for the sidewall and central column along with an evaluation of seismic damage to the station's structure are selected as analytical indicators. This paper uses these indicators to assess the impact of the weak interlayer on the station's seismic response. As shown in Figure 5, the absolute values of the relative horizontal displacement values at points A and B represent the horizontal displacement values for the traditional structure; the absolute values of the relative horizontal displacement values at points C, D and E, F represent the horizontal displacement values of the upper and lower central columns of the station, respectively. Figure 4: Input ground motion acceleration time history curve. (**a**) Chi-Chi earthquake. (**b**) Dzuce earthquake. (**c**) Manjil earthquake. Figure 5: Schematic diagram of the section node. Influence of the position of weak interlayers  
In this condition, a weak interlayer with a thickness of 2 m is assumed, positioned at various heights within the subway station structure, including the upper, top, middle, bottom, and lower sections. A layered site without an interlayer is established for comparison by analyzing these six different conditions to assess the influence of the interlayer's position on structural seismic response. Figures 6-8 present the maximum displacement values of the station's sidewall and central column when the interlayer is located at different positions within the station. Due to the length of the article, input accelerations only consider 0.2 g and 0.4 g in this context. From Figures 6-8, it becomes evident that when the weak interlayer is situated in the middle of the station, it has the most significant seismic impact. When the weak interlayer is at the top or bottom of the subway station structure, it substantially affects the subway station structure. However, when the weak interlayer is placed in the upper or lower sections of the station, its impact is similar to that of the layered site condition, or even less. The weak interlayer effectively separates the soil into upper and lower portions. When the weak interlayer is positioned in the upper or lower sections of the structure, it does not make direct contact with the subway station structure. Consequently, the forces generated by the deformation of the weak interlayer under seismic action do not directly affect the subway station structure, resulting in minimal impact. When the weak interlayer is located at the top or bottom of the station, only half of its thickness is in contact with the subway station structure. The deformation generated by the weak interlayer during seismic action is only partially transferred to the structure. Therefore, its impact on the underground structure is less pronounced compared to the condition where the interlayer is in the middle of the subway station structure. Figure 6: Maximum displacement of the station side wall at different positions. (**a**) 0.2 g. (**b**) 0.4 g.  
Figure 7: Maximum displacement of the station upper column at different positions. (**a**) 0.2 g. (**b**) 0.4 g.  
Figures 9 and 10 depict the tensile damage of the subway station structure when the weak interlayer is positioned at different locations. When DAMAGET approaches 1, it indicates that the concrete has completely cracked under tension. Given the more pronounced seismic response patterns under the Chi-Chi earthquake, this section only illustrates subway station structure tensile damage under 0.2 g and 0.4 g Chi-Chi earthquakes. It can be seen from these illustrations that, compared to the subway station structure situated on a layered soil site, the presence of a weak interlayer at the station's midsection significantly exacerbates the tensile damage of the main subway station structure.