## 5 Analysis of the Influence of Jacking Parameters on Land Subsidence
### Analysis of the Formation Response After Friction Resistance Deviation  
The magnitude of the pipe-soil friction gradually increases with an increasing jacking length of the tunnel. To reduce the limitation of the jacking length, a bentonite slurry was used to reduce the resistance in this project. Figure 11 depicts the variation trend of the vertical displacement of surface B8 at different construction stages under different pipe slurry friction coefficients (0.01-0.09). Before the tail passes through D\({}_{0}\), the jacking length of the tunnel is less than three rings, and the distance is short. The changes in the friction coefficient have no evident influence on the maximum settlement of the ground surface. After the tail passes through the D\({}_{0}\) 6 ring, as the number of jacking segments increases, the increase in the friction coefficient causes a greater increase in the jacking friction, and the maximum increase in the surface settlement is 7.5%. When the tail passes through the D\({}_{0}\) 16 ring, the maximum increase in surface settlement is 22.5%. At this time, the larger friction coefficient further aggravates the development of surface settlement. Therefore, even a small friction coefficient deviation can cause great surface subsidence fluctuations, particularly when the jacking distance increases to a certain extent. After passing through the D\({}_{0}\) 16 ring, the change in the surface settlement trough is shown in Figure 12. When the friction coefficient of the pipe slurry increases from 0.01 to 0.09, the maximum ground settlement increases from 6.68 to 8.18 mm. Compared with the maximum settlement value under the average friction coefficient of 0.03, the maximum settlement increase under the maximum positive deviation is 16.5%, and the maximum settlement decrease under the maximum negative deviation is 4.9%. The distributions of the settlement and uplift areas are not strongly affected by the deviation of the friction coefficient. With an increasing friction coefficient, the settlement area increases only slightly. Figure 11: Influence of the friction coefficient deviation on ground settlement. Figure 10: Comparison diagram of the vertical stress on the soil arch under two kinds of tunnel face pressures: (**a**) \(p_{N}=100\)kPa; (**b**) \(p_{N}=140\)kPa. Figure 13 shows the distributions of vertical rock stress and soil arching when the tail passes 16 rings beyond D\({}_{0}\), with pipe slurry friction coefficients of \(\mu\) = 0.01 and 0.09. Near monitoring section D\({}_{0}\), the area with \(R\) < 0 decreases significantly, while the area with \(R\) > 0 increases significantly, indicating an increase in vertical stress, which also leads to increased settlement in that area. When the jacking distance extends to a certain point, the maximum surface settlement value becomes positively correlated with the pipe slurry friction coefficient. However, the distribution range and position of the arch foot, as well as the stress variation in the soil ahead of the face, are not significantly affected by the pipe slurry friction coefficient. Deviations of the above three jacking parameters from their average values lead to the fluctuations in the maximum surface settlement to varying degrees. Figure 14 shows the normalized vertical displacement of the ground surface caused by the deviation of the jacking parameters, where \(\delta\) and \(\delta_{st}\) represent the vertical displacement of the soil under the average value of the parameters and the deviation value after the tail passes through the monitoring section D\({}_{0}\) 16 ring, respectively. The absolute values of the slopes of the three curves in the figure indicate that among the jacking parameters, the jacking speed has the greatest influence on the surface settlement, followed by the friction coefficient of the pipe slurry; the pressure of the tunnel face has the least effect.