## 3 Calculation Results and Influence Factors Analysis
### Transverse Ground Settlement with Different Excavation Intervals  
For the double-line tunnel with staggered excavation, according to the lateral settlement data of the ground, the lateral ground settlement curves of the tunnel under the excavation intervals of 24 m, 48 m, and 75 m are drawn. To analyze the change in land subsidence caused by the excavation of the right-line tunnel under different longitudinal excavation intervals, Figure 3 also shows the land subsidence curve of the double-line tunnel at the beginning of the excavation of the right-line tunnel. Because the shield shell volume occupies three excavation steps and the fourth excavation step is used for lining assembly, the third excavation step of the right tunnel has a great influence on the ground settlement. Therefore, in the case of longitudinal excavation intervals of 24 m and 48 m, the ground settlement after the 11 th and 19 th excavation steps of the double-line tunnel is extracted and compared with the ground settlement of the same excavation steps of the normal continuous excavation double-line tunnel. In Figure 3, the curves marked by 24-1 and 24-2 are the ground settlement of the double-line tunnel with an excavation interval of 24 m and the continuous excavation of the double-line tunnel at the 11 th excavation step, respectively. The curves marked by 48-1 and 48-2 are the ground subsidence of the double-line tunnel with an excavation interval of 48 m and the double-line tunnel with continuous excavation at the 19 th excavation step, respectively. The curves marked with 24, 48, and 75 are the final ground subsidence of the double-line tunnel under the excavation conditions of longitudinal intervals of 24 m, 48 m, and 75 m. Here, the condition that the longitudinal spacing is 75 m can be regarded as the normal continuous excavation of the double-line tunnel. \begin{table}
\begin{tabular}{c c c} \hline  & **Maximum Settlement Location/m** & **Maximum Settlement/mm** \\ \hline single-line tunnel & - & 3.65 \\ double-line tunnel (1.0D) & \(-\)1.6 & 4.73 \\ double-line tunnel (1.5D) & \(-\)2.67 & 4.34 \\ double-line tunnel (2.0D) & \(-\)4.8 & 3.75 \\ \hline \end{tabular}
\end{table} 
Table 2: Maximum settlement and location of single-line tunnel and double-line tunnel with three tunnel spaces. In Figure 3a and Table 3, under the 1.0D tunnel space, for the continuous excavation of the double-line tunnel, the maximum ground settlement of the 11 th and 19 th steps is located above the axis of the left-line tunnel, and the settlement is the same. For the double-line tunnels with excavation intervals of 24 m and 48 m, the maximum ground subsidence in the 11 th stage is located at 4.8 m on the left side of the central axis of the double-line tunnel. Compared with the continuous excavation tunnel, the ground subsidence increased by 0.21 mm and 0.25 mm, about 5% and 6.7%, respectively. \begin{table}
\begin{tabular}{c c c c c} \hline  & **Location of Maximum** & **Maximum Settlement** & **Location of Maximum** & **Maximum Settlement** \\  & **Settlement (11 Steps)/m** & **Value (11 Steps)/mm** & **Settlement (19 Steps)/m** & **Value (19 Steps)/mm** \\ \hline Double-line tunnel with & \(-6.4\) & \(3.61\) & \(-6.4\) & \(3.71\) \\ continuous excavation & \(-4.8\) & \(3.82\) & - & - \\ (exocation interval 24 m) & - & - & -\(4.8\) & \(3.96\) \\ Double-line tunnel & & & & \\ (exocation interval 48 m) & - & - & -\(4.8\) & \(3.96\) \\ \hline \end{tabular}
\end{table} 
Table 3: Settlement position and settlement value of continuous excavation and staggered excavation double-line tunnel in 1.0D tunnel space. Figure 3: Comparison of transverse ground subsidence caused by staggered excavation and continuous excavation of double-line tunnels with different excavation intervals. (**a**) 1.0D tunnel space; (**b**) 1.5D tunnel space; (**c**) 2.0D tunnel space. The results show that the longitudinal close excavation of the tunnel will cause secondary disturbance to the excavated soil and increase the ground settlement.