## 3 Calculation Results and Influence Factors Analysis
### Quantity Analysis of Influence Factors of Double-Line Tunnel Excavation  
To intuitively analyze the different influencing factors that affect the maximum settlement of the double-line tunnel, for different tunnel spacing and excavation spacing, the maximum point of ground settlement above the axis of the left line, the right line, and the double-line tunnel is considered, as shown in Table 4 and Figure 5. In the following table, the land subsidence of the three largest points is marked by the left line, the right line, and the middle line. The difference between the maximum and minimum values of these three kinds of land subsidence is analyzed by range R, and the importance of the two influencing factors is judged by R analysis.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Distance**} & **2.0D** & **1.5D** & **1.0D** & **R (mm)** \\ \hline \multirow{3}{*}{75 m} & Left line & \(-\)3.46 & \(-\)3.90 & \(-\)4.34 & 0.88 \\  & midline & \(-\)3.52 & \(-\)4.21 & \(-\)4.65 & 1.13 \\  & Right line & \(-\)2.05 & \(-\)2.63 & \(-\)3.34 & 1.29 \\ \hline \multirow{3}{*}{48 m} & Left line & \(-\)3.48 & \(-\)3.92 & \(-\)4.37 & 0.89 \\  & midline & \(-\)3.55 & \(-\)4.25 & \(-\)4.69 & 1.14 \\  & Right line & \(-\)2.10 & \(-\)2.67 & \(-\)3.39 & 1.29 \\ \hline \multirow{3}{*}{24 m} & Left line & \(-\)3.39 & \(-\)3.86 & \(-\)4.33 & 0.95 \\  & midline & \(-\)3.60 & \(-\)4.30 & \(-\)4.73 & 1.13 \\  & Right line & \(-\)2.25 & \(-\)2.80 & \(-\)3.48 & 1.23 \\ \hline \multirow{3}{*}{0 m} & Left line & \(-\)2.76 & \(-\)3.27 & \(-\)3.78 & 1.02 \\  & midline & \(-\)3.59 & \(-\)4.27 & \(-\)4.62 & 1.03 \\  & Right line & \(-\)2.76 & \(-\)3.27 & \(-\)3.78 & 1.02 \\ \hline \multirow{3}{*}{R (mm)} & Left line & 0.72 & 0.65 & 0.59 & \\  & midline & 0.08 & 0.09 & 0.10 & \\ \cline{1-1}  & Right line & 0.71 & 0.64 & 0.44 & \\ \hline \end{tabular}
\end{table}
Table 4: The maximum ground settlement points and R analysis of the left line, right line, and axis of the double-line tunnel under different tunnel spacings and excavation spacings/mm.  
Figure 4: Comparison of the maximum transverse ground settlement caused by staggered excavation and continuous excavation under different tunnel spacings and excavation intervals of a double-line tunnel.  
In Figure 5, when the longitudinal excavation interval is constant, the settlement values of the three points gradually increase with the decrease in the transverse tunnel spacing, and the right-line tunnel is more affected by the change in the transverse tunnel spacing than the left line. The horizontal tunnel space is certain, and the land subsidence of the left line, the middle line, and the right line does not change much in the longitudinal space of 75 m and 48 m. This may reveal that when the longitudinal excavation space is greater than 48 m, the settlement of these points is not affected by the longitudinal excavation spacing. As the longitudinal excavation spacing decreases from 48 m to 24 m, and then to 0 m, the land subsidence of the left line gradually decreases, the land subsidence of the middle line does not change much, and the land subsidence of the right line gradually increases. In addition, with the decrease in the longitudinal excavation interval, the disturbance of the post-ex excavation tunnel to the ground becomes larger and larger, and the land subsidence of the left and right lines becomes larger. In Table 4, the left line with a longitudinal interval of 75 m has the smallest land subsidence range relative to different tunnel spaces, which is 0.8 mm. For the left line with a 2.0D tunnel space, the land subsidence range concerning different excavation intervals is the largest, which is 0.72 mm. The minimum value of the former is greater than the maximum value of the latter, indicating that the lateral spacing of tunnels has a greater effect on ground settlement than the longitudinal excavation distance.