## 5 Analysis of the Influence of Jacking Parameters on Land Subsidence
### Analysis of the Formation Response After Jacking Speed Deviation  
Owing to the complexity of Shanghai's soft soil layer conditions, the jacking speed was set to fluctuate around 5 ring/d. Figure 6 shows the vertical displacement of the surface (B8) directly above the tunnel axis at different construction stages when the jacking speed was 2, 5, 7, and 10 ring/d. With increasing jacking speed, the extrusion effect of the cutter head on the soil in front of the tunnel face also increases, and the surface settlement value gradually decreases, showing that an appropriate increase in the jacking speed can reduce the surface settlement; the slope of each curve also decreases with increasing jacking speed. When the jacking speed exceeds 7 ring/d, the influence of the change in the jacking speed on the surface is very small, indicating that the increase in the jacking speed has only a limited impact on surface subsidence control. When the tail passes through the 16 th ring of the monitoring section, the maximum settlement values of the ground surface at each jacking speed are 8.54, 7.02, 6.40, and 6.13 mm, respectively, and the maximum fluctuation range of settlement is 2.41 mm. When the cutter head has not passed the monitoring section, the maximum fluctuation range of settlement is only 0.74 mm, which also shows that timeliness is important in controlling the jacking speed. When the tail passes through the section with strict surface deformation, the lower jacking speed aggravates the influence of surface settlement in this section. At this time, the lower limit of the jacking speed should be more strictly controlled. Figure 7 shows the change in the surface transverse settlement trough when the tail passes through the rear 16 th ring. Compared with the settlement's extreme value under the average jacking speed, the settlement's extreme value under the maximum positive deviation is reduced by 12.8%, and the settlement's extreme value under the maximum negative deviation is increased by 21.6%; that is, the deviation of the jacking speed is negatively correlated with the fluctuation of the settlement's extreme value. The \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **Jacking Speed** & **Tunnel Face Pressure** & **Coefficient of Friction** \\ \hline Average value & 5 & 105 & 0.03 \\ Value range & [2,10] & [100,140] & [0.01,0.09] \\ Deviation area & [\(-\)60\%,100\%] & [\(-\)4.8\%,33.3\%] & [\(-\)66.7\%,200\%] \\ \hline \end{tabular}
\end{table} 
Table 2: Pipe jacking parameters. Figure 6: Influence of the jacking speed deviation on the ground settlement. deviation in the thrust velocity has little effect on the distribution of subsidence and uplift areas. Taking the average jacking speed as an example, the surface within the range of approximately 3.8 D from the central axis of the tunnel exhibits subsidence, and the areas on both sides show uplift. With increasing jacking speed, the settlement area decreases only slightly. According to the concept of the stress change ratio \(R\) proposed by [PERSON] et al. (2016), the \(R\) value at the arch foot is greater than 0, and the \(R\) value below the soil arch is less than 0. Figure 8 shows the vertical stress soil arching in the surrounding rock under a low jacking speed and under a high jacking speed. The soil in front of the tunnel face is in a shear disturbance zone ([PERSON] and [PERSON], 2017). The soil is squeezed to produce shear deformation, and excess pore water pressure is generated inside. Because the vertical total stress is unchanged, the effective stress is reduced, which is manifested as a blue area. The soil in the rear is a consolidation zone. The soil around the tunnel is disturbed by construction, resulting in excess pore water pressure. Then, it slowly dissipates, the effective stress increases, and the soil consolidates and settles, resulting in a yellow area. The vertical stress soil arch is formed in the upper and lower surrounding rock of the tunnel after the pipe jacking machine is pulled out.