## 4 Calculation Result
### Seismic Mitigation Structure
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Comparative Indicators**} & \multicolumn{2}{c}{**Prototype Structure**} & \multicolumn{2}{c}{**Seismic Mitigation**} & \multicolumn{2}{c}{**Seismic Mitigation Rate**} \\ \hline \multirow{2}{*}{Maximum displacement of side walls} & Chi-chi earthquake & 3.76 mm & 3.99 mm & \(-6.12\%\) \\  & Duzce earthquake & 4.87 mm & 5.18 mm & \(-6.37\%\) \\  & Manjil earthquake & 3.36 mm & 3.58 mm & \(-6.55\%\) \\ \hline \multirow{2}{*}{Maximum displacement of upper middle column} & Chi-chi earthquake & 1.59 mm & 1.89 mm & \(-18.87\%\) \\  & Duzce earthquake & 2.06 mm & 2.45 mm & \(-18.93\%\) \\  & Manjil earthquake & 1.39 mm & 1.67 mm & \(-20.14\%\) \\ \hline \multirow{2}{*}{Maximum displacement of lower middle column} & Chi-chi earthquake & 2.07 mm & 2.94 mm & \(-42.03\%\) \\  & Duzce earthquake & 2.59 mm & 3.72 mm & \(-43.63\%\) \\  & Manjil earthquake & 1.67 mm & 2.42 mm & \(-44.91\%\) \\ \hline \multirow{2}{*}{Maximum bending moment at the bottom of the upper middle column} & Chi-chi earthquake & 72.18 kN-m/m & 25.92 kN-m/m & 64.09\% \\  & Duzce earthquake & 100.5 kN-m/m & 35.54 kN-m/m & 64.64\% \\  & Manjil earthquake & 68.37 kN-m/m & 23.94 kN-m/m & 64.98\% \\ \hline \multirow{2}{*}{Maximum shear at the base of the upper middle column} & Chi-chi earthquake & 53.99 kN/m & 13.34 kN/m & 75.29\% \\  & Duzce earthquake & 73.79 kN/m & 18.07 kN/m & 75.51\% \\  & Manjil earthquake & 49.82 kN/m & 12.25 kN/m & 75.41\% \\ \hline \multirow{2}{*}{Maximum bending moment at the bottom of the lower middle column} & Chi-chi earthquake & 140.5 kN-m/m & 24.25 kN-m/m & 82.74\% \\  & Duzce earthquake & 178.9 kN-m/m & 31.26 kN-m/m & 82.53\% \\ \hline \multirow{2}{*}{Maximum shear at the base of the lower middle column} & Chi-chi earthquake & 17.28 kN-m/m & 21.33 kN-m/m & 81.80\% \\  & Duzce earthquake & 67.62 kN-m & 17.98 kN/m & 73.41\% \\ \hline \multirow{2}{*}{Maximum shear at the base of the lower middle column} & Chi-chi earthquake & 67.62 kN-m & 17.98 kN/m & 73.41\% \\  & Duzce earthquake & 85.79 kN/m & 23.27 kN/m & 72.88\% \\ \hline \multirow{2}{*}{Maximum shear at the base of the lower middle column} & Chi-chi earthquake & 55.92 kN/m & 15.24 kN/m & 72.75\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparative index values of prototype structure and seismic reduction structure under homogeneous site conditions. The internal force seismic mitigation rate at the bottom of the upper middle column and the bottom of the lower middle column under the Chi-chi earthquake is extracted, as shown in Figure 21. It can be seen from the figure that as the thickness of the weak interlayer increases, the seismic mitigation rate of the internal force in the section of the upper middle column tends to decrease, though the minimum value remains close to the bottom of the upper middle column. Figure 20: Displacement seismic mitigation rate of middle columns under different ground shocks. (**a**) Displacement seismic mitigation ratio under the Chi-chi earthquake. (**b**) Displacement seismic mitigation ratio under the Duzce earthquake. (**c**) Displacement seismic mitigation ratio under Manjil earthquake. 60%. For the lower middle column, the seismic mitigation rate of the internal force in the section tends to increase, with the maximum value approaching 85%. This indicates that the application of split columns in underground stations can significantly reduce the internal force in the key sections. As the thickness of the weak interlayer increases, the influence on the seismic mitigation rate of the upper middle column decreases, while the influence on the seismic mitigation rate of the lower middle column increases. 2.2 Influence of the Weak Degree of the Weak Interlayer on the Seismic Mitigation Effect of the Underground Structure  
The thickness of the weak interlayer is set to 3 m, and the shear wave velocity of the weak interlayer is considered to be 150 m/s, 125 m/s, 100 m/s, and 75 m/s, respectively.