# Seismic Response and Mitigation Analysis of a Subway Station in the Site with Weak Interlayers
## 4 Conclusions  
This study investigates the seismic response of the subway station structure with a double-layer double-span rectangular underground foundation. The influence of factors such as weak interlayer thickness, location, and strength on the seismic response of subway station structures is investigated by establishing the two-dimensional finite element model of the soil-structure interaction. This paper proposes a seismic mitigation structure that involves installing FPB on the top of the central column within the subway station. Then, the seismic mitigation effectiveness of FPB in weak interlayer conditions is discussed by the two-dimensional dynamic time history analysis method of the soil structure systems. The main conclusions are as follows:  
(1) When the weak interlayer is situated in the middle of the subway station structure, the seismic effect is most pronounced. If the weak interlayer is located at the top or bottom of the subway station structure, the structural impact is less pronounced. The influence is close to that of a layered soil site condition when the weak interlayer is situated in the upper and lower sections of the station. These patterns become especially evident when the seismic acceleration reaches 0.4 g;  
(2) When the weak interlayer is situated in the middle of the subway station structure, the maximum horizontal displacement of the structure follows a trend of initially decreasing and then increasing with an increase in the thickness of the weak interlayer. The greater thickness of the weak interlayer exacerbates seismic tensile damage to the structure, particularly affecting the central columns and side wall. A weak interlayer thickness of 3 m is the most detrimental to structural safety;  
(3) With the increase in shear wave velocity, there is a decreasing trend in the maximum displacement of the structural side wall and central column. In other words, an increase in the hardness of the weak interlayer can restrain structural deformations and reduce tensile damage to the structural side wall;  
(4) In comparison to the original structure, the installation of FPB on the top of central columns reduces the overall structural lateral stiffness of the station, resulting in a slight increase in the maximum displacement of the side wall and the inter-story displacement angle of the upper and lower levels of the subway station structure. It also increases tensile damage to the side wall;  
(5) The installation of FPB effectively reduces the deformation of central columns, especially under strong seismic conditions (0.4 g), the maximum reduction could reach 36 mm. This effectively reduces tensile damage of the central column but simultaneously transfers damage at the connection points of the top and bottom slabs with the central columns to the connection points with the side wall;  
(6) The seismic mitigation scheme with FPB on the top of central column of subway station structure significantly reduces the internal forces in the central column. The most  
Figure 31: Decreasing amplitude ratio of the force of structure under the Chi-Chi earthquake. (**a**) Bending moment. (**b**) Shearing force. (**c**) Bending moment. (**d**) Shearing force. pronounced seismic reduction is observed in shear forces, with a reduction rate of up to nearly 95%. In complex site conditions involving weak interlayers, the seismic reduction effect of the seismic mitigation structure is superior to that of layered ground conditions. In general, based on the findings of this study, it is evident that a weak interlayer has an adverse impact on the seismic performance of station structures. The installation of FPB on the top of the central column of the subway station structure effectively reduces seismic damage to the structure. The proposed seismic mitigation scheme in this paper is suitable for situations where the subway station structure is located in a weak interlayer site. Additionally, the seismic mitigation effectiveness in weak interlayer sites surpasses that in layered soil sites.