## 5 Conclusions  
This paper considers the two-story double-span rectangular frame underground station as the research object. A two-dimensional numerical model is established using the finite element analysis software ABAQUS. The soil-underground structure overall dynamic time-history analysis is adopted to study the effect of the soft interlayer thickness and soil condition (i.e., shear wave velocity) on the seismic response of the underground station structure. The seismic mitigation effect of the structure formed by the use of split columns is compared with that of the prototype structure in terms of the lateral displacement rate of key components and the seismic mitigation rate. The following conclusions are drawn:  
1. The quasi-static test results from the numerical simulation and model test show good agreement. The same conclusion can be drawn from the skeleton curves of both the numerical simulation and the model test. When the horizontal load reaches its peak, the traditional column is found to be approximately 55% larger than the split column;
2. Under earthquake action, when the weak interlayer passes through the underground station, the deformation of the key components of the underground structure increases, and the internal force at the bottom of the middle column also increases. As the thickness of the weak interlayer increases, the relative displacement and internal force of the key components also increase. Additionally, with the increase in  
Figure 26: Soil-structure stiffness ratios for different degrees of softness in soft interlayers. Figure 25: Soil-structure stiffness ratios for different weak interlayer thicknesses. weak interlayer thickness, the dynamic response of the interlayer thickness to the underground structure is gradually weakened;
3. The softer the soil in the weak layer passing through the underground structure (the smaller the shear wave velocity), the greater the relative displacement and internal force of the key components. With the decrease in shear wave velocity, the influence of weakness on the seismic response of underground structures is gradually enhanced;
4. Compared to the prototype structure, the use of split columns in the underground structure results in a reduction in the overall stiffness of the structure, leading to an increase in the horizontal displacement of the structure;
5. The application of split columns in underground structures can significantly reduce the internal forces in key sections. The most pronounced seismic mitigation effect is observed in the bending moment at the bottom of the lower middle column, where reductions of up to 85% can be achieved. In general, at weak interlayer sites, the seismic performance of the station structure can be effectively improved by replacing the ordinary columns with split columns in the subway station structure. The worse the soil quality of the weak layer, the more significant the seismic mitigation effect, making it an effective seismic mitigation measure. This paper only considers the weak interlayer passing through the middle of the subway station. The influence of weak interlayers in other locations and additional factors require further research and analysis. Conceptualization, Z.X. ([PERSON]) and Z.X. ([PERSON]); methodology, Z.X. ([PERSON]); software, Z.X. ([PERSON]); validation, [PERSON] ([PERSON]); formal analysis, [PERSON] ([PERSON]); data curation, [PERSON] ([PERSON]); writing--original draft preparation, [PERSON] ([PERSON]); writing--review and editing, [PERSON] ([PERSON]); visualization, [PERSON] ([PERSON]); project administration, [PERSON] ([PERSON]); funding [PERSON], [PERSON] ([PERSON]) and [PERSON] ([PERSON]). All authors have read and agreed to the published version of the manuscript. This research is jointly funded by the National Natural Science Foundation of China (No. 52108453), the Natural Science Foundation of Jiangxi Province (No. 20212 BAB214014 and No. 20232 BAB204084), the China Postdoctoral Science Foundation Project (No.