## 3 Results and Analysis
### Evolution Law of Surface Subspace
#### 3.2.2 Numerical Simulation Results  
It can be seen from the above field monitoring analysis that the strata within the range of 0.5 times the outer diameter of the shield (0-3 m) above the tunnel produce large settlement deformation. In order to intuitively reflect the settlement law, the numerical simulation results of stratum settlement at 3 m above the tunnel are compared with the field measured values, as shown in Figure 10. Tables 5-7 show the variation of the proportion of stratum settlement at 3 m above holes 1 # through 3 # tunnel in total settlement with different stages of shield tunneling.  
Combined with the chart analysis, it can be seen that the deviation between the field monitoring value and the numerical simulation result is small, the overall change trend is basically consistent, and the settlement in the shield tail stripping stage accounts for the largest proportion. Among them, the settlement of shield approaching stage (\(-\)30-0 m) is small. Taking the hole 2 # with the largest settlement proportion in this stage as an example, its settlement accounts for 22.8% of the total settlement, while the corresponding numerical simulation settlement accounts for about 11.0% of the total settlement. With the continuous advancement of tunnel excavation, the settlement deformation rate continues to increase, and the settlement proportion of shield crossing stage (0-6 m) continues to increase. The field measurement shows that this stage accounts for 27.9%, 28.4% and 38.0% of the three holes respectively, reaching about 1/3 of the total settlement. At this stage, the proportion of settlement based on numerical simulation also continued to increase, but the overall increase rate was low. The reason for this difference may be that the stratum was disturbed for a longer time during the actual construction process. Based on the field monitoring and numerical simulation results, the proportion of settlement is greater than 40% in the shield tail detachment stage (6-30 m). At this stage, the stratum settlement increases significantly and is the main settlement stage.  
Figure 9: Layered subsidence time history curve of monitoring section stratum. (**a**) hole 1 #. (**b**) hole 2 #. (**c**) hole 3 #.  
Figure 10: _Cont_.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Transverse Distance (m)** & \(-\)**30\(-\)0** & **0\(-\)6** & **6\(-\)30** & **Total** \\ \hline Field monitoring (mm) & \(-\)2.73 & \(-\)3.41 & \(-\)5.85 & \(-\)11.99 \\ Ratio & 22.8\% & 28.4\% & 48.8\% & / \\ Numerical simulation (mm) & \(-\)1.28 & \(-\)1.86 & \(-\)8.46 & \(-\)11.60 \\ Ratio & 11.0\% & 16.0\% & 73.0\% & / \\ \hline \hline \end{tabular}
\end{table}
Table 6: The stratum settlement value at 3 m above the tunnel at different stages of shield tunneling in hole 2 #.  
Figure 10: Layered settlement time history curve of stratum at 3m above the tunnel. (**a**) hole 1 #. (**b**) hole 2 #. (**c**) hole 3 #.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Transverse Distance (m)** & \(-\)**30\(-\)0** & **0\(-\)6** & **6\(-\)30** & **Total** \\ \hline Field monitoring (mm) & \(-\)2.65 & \(-\)3.29 & \(-\)5.84 & \(-\)11.78 \\ Ratio & 22.5\% & 27.9\% & 49.6\% & / \\ Numerical simulation (mm) & \(-\)1.14 & \(-\)1.20 & \(-\)9.20 & \(-\)11.54 \\ Ratio & 9.9\% & 10.4\% & 79.7\% & / \\ \hline \hline \end{tabular}
\end{table}
Table 5: The stratum settlement value at 3 m above the tunnel at different stages of shield tunneling in hole 1 #.