## 4 Control Effect of Ground Improvement on Influenced Zone of Deep Excavation
### Effect of Ground Improvement on Influenced Zone of Deep Excavation  
The ground improvement outside the pit changes the displacement characteristics of the existing tunnel, so it inevitably changes the influenced zone of deep excavation on tunnel displacement. The following will focus on the redistribution of the influenced zone after ground improvement. The method for dividing the influenced zone is consistent with that of Section 2.3. By setting the different positions of the tunnel outside the pit, numerical simulations are adopted to calculate the tunnel displacement induced by excavation. On this basis, through the analysis of tunnel displacement isoline, combined with 3-level tunnel displacement control standards, the scope of the influenced zone corresponding to each control standard is divided.  
Figure 15 shows the horizontal and vertical displacement isolines of the tunnel at different positions after ground improvement. Compared with the results in Figure 3 without ground improvement, the tunnel displacement decreases obviously with the maximum horizontal displacement not exceeding 15 mm and the maximum vertical displacement  
Figure 14: The maximum displacement of tunnels at different positions after ground improvement: (**a**) horizontal displacement; (**b**) vertical displacement.  
not exceeding 10 mm, and the scope of the isoline corresponding to the same displacement control standard decreases.  
Then, according to the division method for the influence zone of deep excavation on adjacent tunnel displacement in Section 2.3, the influenced zone corresponding to the 3-level tunnel displacement control standards is given after ground improvement. The range outside the pit is divided into: II--secondary influenced zone, III--general influenced zone, and IV--weak influenced zone, as shown in Figure 16. The determination parameters of the scope of the influenced zone after ground improvement are listed in Table 5.  
Compared with the division results of the influenced zone without ground improvement in Table 3, the scope of the influenced zone is significantly reduced, and the I--primary influenced zone corresponding to the tunnel displacement control standard of 20 mm no longer exists; the width and depth of the II--secondary influenced zone is reduced by 60% and 30%, respectively. The width and depth of III--general influenced zone are reduced  
Figure 16: Influenced zones of deep excavation on adjacent tunnel displacement after ground improvement.  
Figure 15: Isolines of tunnel displacement after ground improvement: (**a**) horizontal displacement isoline; (**b**) vertical displacement isoline.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **20 mm** & \multicolumn{5}{c}{**10 mm**} & \multicolumn{5}{c}{**5 mm**} \\ \hline \(M\) & \(N_{1}\) & \(N_{2}\) & \(M\) & \(N_{1}\) & \(N_{2}\) & \(M\) & \(N_{1}\) & \(N_{2}\) \\ / & / & / & 0.55 & 1.45 & 1.75 & 0.90 & 1.75 & 2.50 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Determination parameters of the scope of influenced zones after ground improvement.  
by 60% and 26%, respectively. Therefore, it is concluded that the ground improvement outside the pit plays an important role in reducing the influenced zone of deep excavation on adjacent tunnel displacement.