# Synchronous Grouting Analysis of Shield Tunneling through High Water Pressure Fault Fracture Zone
## 5 On Site Monitoring of Soil and Water Pressure
### Analysis of Monitoring Results
Figure 40: Change in pore water pressure of J3. Figure 34:0 Change in soil pressure at J9 monitoring point. Based on the monitoring data of the J3 borehole pore water pressure sensor, the variation trends of pore water pressure at the top, middle, and bottom are obtained. From Figure 40, it can be seen that the variation pattern of soil pressure at the bottom, middle, and top of shield tunneling is the same at the same time. As the shield tunneling progresses, the pore water pressure in the surrounding rock is gradually reduced due to disturbance. When the shield tunneling machine is closer to the monitoring point, the changes in pore pressure are severe, while as the shield tunneling machine moves away, the impact on soil pressure gradually decreases. Compared to Figure 35, the variation patterns of pore pressure and soil pressure are basically consistent. As shown in Figure 41, the variation of the pore water pressure sensor in the middle of J9 during the entire process of shield tunneling through the fault fracture zone is the same as the previous text. The purple line represents the change of soil pressure at the monitoring point with excavation time, and the red line represents the excavation ring number at that time. In Figure 41, the purple and red lines represent the pore pressure and ring number, respectively. According to the monitoring of pore water pressure changes in the central part of J9 borehole, it can be concluded that the variation pattern of pore water pressure is consistent with that of J9 soil pressure, and there are three influencing areas: the main influencing area, the secondary influencing area, and the non-influencing area. The shield tunneling enters the secondary impact zone, and the pore water pressure begins to fluctuate significantly; entering the main influence zone between rings 1485-1567, the pore water pressure fluctuates violently. Similarly, J9 and J6 monitoring points close to the fault and J4 monitoring points farther away from the fault were selected for analysis. The distance between the monitoring section of the shield tunneling and the changes in pore water pressure are shown in Figures 42-44. In Figures 42-44, black, red, and blue represent the pore pressure at the bottom, middle, and top, respectively. (1) Before the shield tunneling reaches the monitoring section, the pore water pressure slowly decreases and the change in pore pressure is relatively small. However, when the shield tail synchronous grouting reaches the monitoring section, the pore pressure significantly increases. At J4 monitoring point, the change in pore pressure is consistent with the change in soil pressure, and the increase in pore pressure continues for a period of time before falling back to the initial level; at monitoring points J6 and J9, the pore water pressure changes significantly upon the arrival of the shield machine and continues to increase. When the shield tail is synchronously grouted, the excess pore pressure reaches its maximum. (2) From the figure, it can be seen that the main reason for the fluctuation of pore water pressure during synchronous grouting is that the change in top pore pressure is relatively small in the same measuring hole, indicating that the scope of influence of synchronous grouting during construction is limited and decreases with increasing distance. (3) Compared to the changes in pore pressure of J4, the changes in excess pore pressure of J6 and J9 during shield tunneling are relatively small. The maximum excess pore water pressure from the excavation face to synchronous grouting is 18 kPa and 22 kPa, respectively, while the maximum excess pore water pressure of J4 is 30 kPa. This may be due to the fact that the J9 test hole is closer to the fault fracture zone, with the development of fractures around the fault, and the rapid dissipation of pore pressure caused by grouting pressure, resulting in low pore pressure during excavation monitoring. Figure 34:1 Change in pore water pressure at J9 monitoring point.