## 3 Measured Analysis of Stratum Deformation  
### Surface Settlement Analysis  
Surface settlement is one of the most important indicators to measure the safety of shield tunneling. If the settlement exceeds the allowable value of field monitoring, it will cause pavement collapse, endanger the safe use of surrounding buildings, and even cause engineering accidents. The specific layout of field monitoring of the surface section of the south line is shown in Figure 3a. The surface cumulative deformation curve of section A is shown in Figure 5. The data are obtained from the cumulative deformation values of section measuring points in the daily monitoring report. The positive value represents the surface heave and the negative value represents the surface settlement. The results show that due to the comprehensive influence of thrust force, grouting pressure, shield tail void, and other factors, the surface deformation of the section experienced the changing trend of the first heave and then settlement, which is distributed in the Gauss curve. During the period of the cutter passing through the section, it is affected by grouting at the shield tail. As can be seen from Figure 5a, the maximum heave value of the ring 330 section reaches 3.09 mm, which increases by 2.02 mm compared with the deformation before reaching the measuring point. Figure 5b shows that the maximum heave value of the ring 350 section is 4.11 mm, which increases by 2.27 mm compared with the deformation before reaching the measuring point. The shield tail prolapse products voids so that the overlying soil moves downward, resulting in large settlements on both sections. After the cutter passes far away from the monitoring section, the settlement increases further with the dissipation of excess pore water pressure, consolidation, and compression of soil. The final settlement of the ring 330 section is \(-\)2.21 mm, and that of the ring 350 section is \(-\)1.96 mm. The specific layout of the surface section of the north line is shown in Figure 3b. The cumulative surface deformation curve of section B is shown in Figure 6. The results show that during shield tunneling, the surface section experiences a continuous settlement process. The surface deformation is relatively gentle before the cutter reaches the front of the section, and the curve law conforms to the Peck settlement curve. Comparing Figure 6a with Figure 6b, the maximum settlement of the ring 350 ring is \(-\)1.68 mm and that of the ring 370 section is \(-\)1.88 mm during the crossing section. After the shield tail passed through the section, the soil collapsed into the gap at the shield tail, and the two sections caused large settlements of \(-\)3.96 mm and \(-\)4.35 mm, respectively. After the cutter passes far away from the section, the settlement is further increased due to soil consolidation and compression. The final settlement of the ring 350 section is \(-\)5.18 mm and the ring 370 section is \(-\)5.45 mm. From the above analysis, it can be seen that the settlement caused by different shield tunneling stages differs. Tables 2 and 3 calculate the proportion of surface deformation caused by each shield tunneling stage of the double line. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**Stage of Shield Tunneling**} \\ \cline{2-6}
**Monitoring** & **Cutter before** & **Cutter below** & **Crossing Section** & **Tail Pass Section** & **Final Settlement** \\ \hline SSP-S-330 & 13\% & 19\% & 5\% & 57\% & 6\% \\ SSP-S-350 & 18\% & 16\% & 6\% & 42\% & 18\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Proportion of surface deformation during construction of the south line. Figure 5: Surface section deformation of the south line: (**a**) SSP-S-330; (**b**) SSP-S-350.