## 4 Results of the Study
### Unreinforced Surface Settlement Analysis  
In the unreinforced section, the shield tunnel boring process will inevitably cause ground movement, which will lead to surface settlement. If the settlement is too large, it may cause serious impacts on the neighboring buildings and the environment, so the construction parameters need to be strictly controlled. In this study, four monitoring points (mileage 5700, 5730, 5760, and 5790) above the centerline of the tunnel in the unreinforced section are selected to analyze the change rule of surface settlement. The horizontal coordinate is the position of the cutter plate incision during shield tunnel excavation, and the vertical coordinate is the amount of surface settlement, and the variation in settlement with shield tunneling is shown in Figure 6.  
Figure 5: Three-dimensional numerical analysis of the numerical simulation section of the Wunan Formation Railway tunnel underneath the interval. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Layers** & \multicolumn{2}{c}{**Borehole-1**} & \multicolumn{2}{c}{**Borehole-2**} & \multicolumn{2}{c}{**Borehole-3**} & \multicolumn{2}{c}{**Borehole-4**} \\
**Materials** & **Top (m)** & **Bottom** & **Top** & **Bottom** & **Top** & **Bottom** \\  & **(m)** & **(m)** & **(m)** & **(m)** & **(m)** & **(m)** & **(m)** \\ \hline (1-2) Plain fill & \(0.00\) & \(-3.20\) & \(0.00\) & \(-3.20\) & \(0.00\) & \(-3.50\) & \(0.00\) & \(-3.50\) \\ (3-1) Silty clay & \(-3.20\) & \(-3.20\) & \(-3.20\) & \(-3.20\) & \(-3.50\) & \(-6.00\) & \(-3.50\) & \(-6.00\) \\ (3-4) Silty clay & \(-3.20\) & \(-10.40\) & \(-3.20\) & \(-10.40\) & \(-6.00\) & \(-11.30\) & \(-6.00\) & \(-11.30\) \\ (7-2) Silty clay & \(-10.40\) & \(-13.40\) & \(-10.40\) & \(-13.40\) & \(-11.30\) & \(-11.30\) & \(-11.30\) & \(-11.30\) \\ (7-3) Silty clay & \(-13.40\) & \(-16.60\) & \(-13.40\) & \(-16.60\) & \(-11.30\) & \(-11.30\) & \(-11.30\) & \(-11.30\) \\ (8-1) Silty sand & \(-16.60\) & \(-26.50\) & \(-16.60\) & \(-26.50\) & \(-11.30\) & \(-17.00\) & \(-11.30\) & \(-17.00\) \\ (8-1a) Silty clay & \(-26.50\) & \(-26.50\) & \(-26.50\) & \(-26.50\) & \(-17.00\) & \(-23.80\) & \(-17.00\) & \(-23.80\) \\ (15a-1) Strongly weathered & \(-26.50\) & \(-42.90\) & \(-26.50\) & \(-42.90\) & \(-23.80\) & \(-43.80\) & \(-23.80\) & \(-43.80\) \\ mudody silstone & \(-42.90\) & \(-50.00\) & \(-42.90\) & \(-50.00\) & \(-43.80\) & \(-50.00\) & \(-43.80\) & \(-50.00\) \\ muddy silstone & \(-42.90\) & \(-50.00\) & \(-42.90\) & \(-50.00\) & \(-43.80\) & \(-50.00\) & \(-43.80\) & \(-50.00\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Settings of drilling information in PLAXIS 3D software. As can be seen from Figure 6, the change in surface settlement during shield tunneling can be divided into the following stages: when the cutter disk is close to the measurement point, the soil in front of the cutter disk may be slightly deformed due to the cutter disk perturbation and the effect of the soil silo pressure, which may be manifested as a bulge or settlement. If there is a bulge, it may be due to the pressure of the soil bin; if there is settlement, it may be caused by soil disturbance. As the cutter disk approaches the measurement point, the change in surface displacement gradually increases; when the cutter disk leaves the measurement point, the displacement continues to increase. When the shield tail is close to the measurement point, the surface settlement may further increase due to the shield tail detachment, but the synchronized grouting will compensate for part of the settlement, and even a slight bulge may occur if the grouting pressure and the grouting volume are larger. When the shield tail moves away from the measurement point, the surface displacement gradually stabilizes. In addition, due to the influence of the measurement time interval, the flattening section of the cumulative displacement curve at some measurement points is not obvious.