## 4 Deformation Characteristics of Site  
### Ground Settlements along the Direction of Tunneling  
Figure 6 shows the variation in ground settlement at monitoring points directly above the axis of the left tube and of the right tube during shield driving, in which, when the cutter head of shield machine does not reach the monitoring section, the distance from the working face to the monitoring section is taken as negative value; otherwise, the distance from the working face to the monitoring section is taken as positive value. D is the diameter of the cutter head of the shield machine, and D equals 6280.00 mm in this project. The tunneling process of this project starts with the excavation of the left hole after completing the excavation of the right hole. Figure 6a gives the history curve of ground settlements during the shield tunneling of the right tube. It is found that the settlements of monitoring points A\({}_{2}\), B\({}_{2}\), and C\({}_{2}\) are smaller than those of the monitoring points A\({}_{1}\), B\({}_{1}\), and C\({}_{1}\), due to the disturbance induced by the excavation of the right tube to monitoring point A\({}_{2}\), B\({}_{2}\) and C\({}_{2}\) is smaller than to monitoring point A\({}_{1}\), B\({}_{1}\) and C\({}_{1}\). Because of the dynamic adjustment of shield tunneling parameters, the response of different monitoring points is slightly different, but the overall settlement characteristics are basically the same. From Figure 6a, the ground settlement at the monitoring points can be divided into five stages with the shield advance. **Stage I. Small disturbance deformation**. When the monitoring section is more than 3D ahead of the working face, the deformation of the monitoring point is tiny. The ground may produce small settlement or uplift due to the loss of the stratum in front of the working face caused by the extrusion of the cutter head of the shield machine and excavation unloading. **Stage II: Slow growth of deformation. ** When the monitoring section is \(-1\)D to \(-3\)D away from the working face, the cutter head of the shield machine is close to the monitoring section, and the deformation of stratum at the monitoring section is greatly affected by the earth chamber pressure acting on the working face, which shows ground subsidence or \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Structural** & **Density/(kg/m3)** & **Elastic** & **Poisson** & **Conversion** & **Clearance Value** \\
**Members** & **Modulus/GPa** & **Ratio** & **Coefficient** & **of Shield Tail/m** \\ \hline Segmental lining & 2500.0 & 35.0 & 0.2 & - & - \\ Shield shell & 2500.0 & 200.0 & 0.2 & - & - \\ Clearance element & & 1.0\%.Es & - & - \\ Equivalent layer & & 0.22 & 0.2 & 1.0 & 0.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Mechanic parameters of structural members [26]. Figure 6: The settlement of the monitoring points following the movement of the working face. (**a**) The shield tunneling of the right tube; (**b**) the shield tunneling of the left tube. uplift. At this stage, stress release occurs in the stratum near the monitoring point. In order to ensure the stability of strata at the working face, the earth chamber pressure of the shield machine needs to be corrected in time. **Stage III: Rapid growth of deformation**. When the working face is within 1D be-hind or ahead of the monitoring section, settlement increases and deformation grows rapidly. At this stage, when the cutter head of the shield machine passes through the monitoring section, there is a small gap between the shield shell and the surrounding strata, and sliding shear occurs at the interface between the shield fuselage and the surrounding strata; thus, the strata produce great disturbance. In this project, the ground settlement reaches 29% to 44% of the final settlement when the working face reaches the monitoring section position. **Stage IV: Deformation increases abruptly again**. When the monitoring section is 1D to 3D behind the working face, the shield tail moves gradually away from the monitoring section.