## 4 Numerical Simulation Analysis
### Influence of Burial Depth
#### 4.4.1 Displacement Responses  
Layer drifts and drift angles under 0.20 g are shown in Table 13 under El-Centro motion. (1) With the increase in buried depth, the relative horizontal displacements in the X-direction first increase and then decrease, and then reach the maximum values when the buried depth is 7.0 m. Simultaneously, the relative horizontal displacements in the Y-direction first decrease and then increase and reach the maximum values when the buried depth is 1.2 m. The layer drift of each floor has the same trend and the maximum layer drift angle value in the X-direction reaches 1/809 (the third underground floor when the buried depth is 7.0 m), which is close to the limit value of 1/800 stated in Code for seismic design of buildings (2010, China). (2) It is usually believed that the deeper the structures are buried, the safer they are under earthquake motions. However, the rule is unsuitable for some special industrial structures such \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Section** & **M1** & **M2** & **M3** & **M4** & **M5** \\ \hline \multirow{4}{*}{Floor 3} & layer drift in the X-direction & 1.76 & 2.25 & 2.42 & 3.06 & 2.97 \\  & layer drift angle in the X-direction & 1/2898 & 1/2267 & 1/2107 & 1/1667 & 1/1717 \\  & layer drift in the Y-direction & 4.03 & 2.88 & 3.82 & 4.01 & 3.91 \\  & layer drift angle in the Y-direction & 1/1266 & 1/1770 & 1/1335 & 1/1271 & 1/1304 \\ \hline \multirow{4}{*}{Floor 2} & layer drift in the X-direction & 1.65 & 2.10 & 2.23 & 2.69 & 1.81 \\  & layer drift angle in the X-direction & 1/2909 & 1/2286 & 1/2152 & 1/1784 & 1/2652 \\ \cline{1-1}  & layer drift in the Y-direction & 3.81 & 2.74 & 3.60 & 3.76 & 3.62 \\ \cline{1-1}  & layer drift angle in the Y-direction & 1/1260 & 1/1752 & 1/1333 & 1/1277 & 1/1326 \\ \hline \multirow{4}{*}{Floor 1} & layer drift in the X-direction & 1.79 & 2.25 & 2.36 & 5.93 & 2.83 \\ \cline{1-1}  & layer drift angle in the X-direction & 1/2682 & 1/2133 & 1/2034 & 1/809 & 1/1696 \\ \cline{1-1}  & layer drift in the Y-direction & 3.83 & 2.74 & 3.59 & 3.76 & 3.73 \\ \cline{1-1}  & layer drift angle in the Y-direction & 1/1253 & 1/1752 & 1/1337 & 1/1277 & 1/1287 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Layer drift (mm) and drift angle (rad) under El-Centro motion. \begin{table}
\begin{tabular}{l l c c c c c c} \hline \hline  & **Section** & \multicolumn{4}{c}{**Shear Force (10\({}^{5}\) N/m)**} & \multicolumn{4}{c}{**Bending Moment (10\({}^{3}\) N-m/m)**} \\ \cline{3-8}  & & **M1** & **M2** & **Increase (\%)** & **M1** & **M2** & **Increase (\%)** \\ \hline \multirow{2}{*}{Side wall 1} & El-Centro motion & 6.53 & 5.80 & 12.59 & 135 & 122 & 10.66 \\  & Lanzhou motion & 6.01 & 5.49 & 9.47 & 130 & 117 & 11.11 \\ \hline \multirow{2}{*}{Side wall 3} & El-Centro motion & 10.98 & 9.79 & 12.16 & 947 & 850 & 11.41 \\  & Lanzhou motion & 9.76 & 8.68 & 12.44 & 893 & 812 & 9.98 \\ \hline \multirow{2}{*}{Side wall 4} & El-Centro motion & 11.08 & 9.42 & 17.62 & 650 & 542 & 19.93 \\  & Lanzhou motion & 9.43 & 8.10 & 16.42 & 818 & 683 & 19.77 \\ \hline \multirow{2}{*}{Side wall 5} & El-Centro motion & 11.70 & 10.57 & 10.69 & 1234 & 1132 & 9.01 \\  & Lanzhou motion & 10.02 & 8.83 & 13.48 & 566 & 517 & 9.48 \\ \hline \multirow{2}{*}{Side wall 6} & El-Centro motion & 3.76 & 3.16 & 18.99 & 126 & 109 & 15.60 \\  & Lanzhou motion & 3.89 & 3.31 & 17.52 & 99 & 87 & 13.79 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Peak internal forces of the side wall. as an underground substation. The reasons are that equipment of high quality and stiffness with complex shapes makes displacements of structure complicated, and overlaying soil reduces the overall displacement of the structure with the increase in buried depth. The layer drift is critical in the Y-direction when the buried depth is shallow, while it is critical in the X-direction with the increase in buried depth.