## 4 Calculation Result
### Seismic Mitigation Structure  
In this section, a comparison and analysis of the split column structure and the ordinary column structure are performed from the perspectives of structural deformation and cross-sectional internal force, and the seismic mitigation effect of the split column is discussed. In terms of deformation, this study selects the relative horizontal displacement at the top and bottom of the side wall, as well as the relative horizontal displacement at the top and bottom of the upper middle column and the lower middle column. In terms of internal force, the shear force and bending moment at the bottom of the upper middle column and the bottom of the lower middle column are selected to compare the differences between the prototype structure and the seismic mitigation structure. The comparison index is expressed by the seismic mitigation rate in this study. The formula is  
\[\delta=\frac{N_{0}-N_{R}}{N_{0}} \tag{6}\]  
In the equation, under the same conditions, \(N_{0}\) represents the internal force values within the top and bottom cross-sections of the central columns of the prototype structure, while \(N_{R}\) represents the internal force values within the top and bottom cross-sections of the central columns of the seismic mitigation structure. The comparative values for the prototype structure and the seismic mitigation structure under the homogeneous site are extracted, as shown in Table 4. The table shows that, in terms of structural deformation, the seismic mitigation rate is negative, indicating that the horizontal displacement of the key components of the seismic mitigation structure is greater than that of the prototype structure. The absolute value of the seismic mitigation rate for the lower middle column is the largest, reaching 40%. In terms of internal force, the  
Figure 19: Internal force value at the bottom of the central column in different cases. (**a**) Maximum shear at the base of the upper middle column. (**b**) Maximum bending moment at the bottom of the upper middle column. (**c**) Maximum shear at the base of the lower middle column. (**d**) Maximum bending moment at the bottom of the lower middle column. seismic mitigation effect of the seismic mitigation structure exceeds 60%, and the bending moment at the bottom of the lower middle column reaches 80%. This indicates that the use of the split column instead of the prototype integral column can effectively reduce the internal force of the key components. 2.1 Influence of the Thickness of the Weak Interlayer on the Seismic Mitigation Effect of the Underground Structure  
The shear wave velocity of the weak interlayer is 125 m/s, and the thickness of the weak interlayer crossing the middle of the underground structure is set to 1 m, 2 m, 3 m, and 4 m, respectively. Four working conditions with different soil thicknesses and one condition without a weak interlayer were established to study the influence of weak interlayer thickness on the seismic mitigation effect of underground structures. Figure 20 shows the seismic mitigation rate of the displacement of the upper and lower middle columns under different ground motions. It can be observed from the figure that the seismic mitigation rate of the upper and lower middle columns under various working conditions is negative, indicating that the displacement of the seismic mitigation structure under earthquake action is greater than that of the prototype structure.