## 4 Numerical Realization of Zero-Distance Construction Process
### Analysis of the Deformation Control Effect and the Mechanical Response of the Existing Tunnel  
When the construction is completed, the vertical deformation curves of the existing tunnel structure floor are shown in Figures 5 and 6. The data points in the figure are distributed along the longitudinal and transverse directions of the existing tunnel and pass through the center point, which is the projection point of the planar geometric center of the underground area on the floor of the tunnel structure. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Name**} & \multirow{2}{*}{\begin{tabular}{c} **Density** \\ **(kg/m3)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Cohesion** \\ **(kPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Slope of** \\ **solidation** \\ **Curve \(\lambda\)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Friction** \\ **Rebound** \\ **Curve \(\kappa\)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Efficient** \\ **Con-** \\ **stant** \\ **M** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Efficient** \\ **Angle** \\ **\(\varphi\) **(\({}^{\circ}\))** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Elastic** \\ **Modulus** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Poisson’s** \\ **Ratio \(\lambda\)** \\ \end{tabular} } \\ \hline
1 & Miscellaneous fill & 1940 & 15.1 & - & - & - & 4.5 & 18.75 & 0.37 \\
2 & Mucky soil & 1610 & 10.2 & 0.128 & 0.024 & 0.98 & 13.5 & 12.15 & 0.41 \\
3 & Silty clay & 2040 & 27.0 & 0.088 & 0.017 & 1.13 & 17.0 & 28.25 & 0.33 \\
4 & Completely & 1970 & 30.2 & - & - & - & 22.4 & 23.7 & 0.28 \\
5 & Strongly weathered & & & & & & & & \\ sandstone & & 2030 & 36.0 & - & - & - & 32.3 & 27.9 & 0.28 \\
6 & Moderately & & & & & & & & \\ weathered sandstone & & & & & & & & & \\ slightly weathered & & & & & & & & & \\ sandstone & & 2520 & 300.0 & - & - & - & 42.5 & 6250 & 0.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Physical and mechanical parameters of strata. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Name**} & \multirow{2}{*}{\begin{tabular}{c} **Density \(\rho\)** \\ **(kg/m3)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Elastic Modulus \(E\)** \\ **(GPa)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Poisson’s Ratio \(\lambda\)** \\ **-** \\ \end{tabular} } \\ \hline \multicolumn{2}{c}{Foundation pit retaining structure} & 2500 & 30.0 & 0.2 \\ \multicolumn{2}{c}{Existing tunnel structure (C30)} & 2500 & 30.0 & 0.2 \\ \multicolumn{2}{c}{Plate and wall of the station main structure (C35)} & 2500 & 31.5 & 0.2 \\ \multicolumn{2}{c}{Column of the station main structure (C50)} & 2500 & 34.5 & 0.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Calculation parameters of concrete structure. Figure 4: Model of existing tunnel and newly built station. Figure 5: Vertical deformation curve of the existing tunnel (longitudinal). It can be seen from Figure 5 that the excavation of the undercrossing area makes the tunnel lose the support of the lower soil mass, the tunnel produces certain overall vertical deformation, and the settlement curve is in a \"U\" shape. At the end of excavation, the vertical displacement of the existing tunnel in Scheme I is the largest, reaching about 3.5 mm, and the settlement of Scheme II and Scheme III is relatively small, about 2.5 mm and 1.9 mm, respectively, indicating that Scheme II and Scheme III have good effects on the vertical deformation control of the existing tunnel. The vertical displacement of the existing tunnel is largest near the central point and remains high throughout the underground excavation area. The vertical deformation value of the tunnel at the edge of the undercrossing area in Scheme I is about 54-70% of the central point, and that in Scheme II and Scheme III is about 40-52% and 39-60%, respectively.