# Synchronous Grouting Analysis of Shield Tunneling through High Water Pressure Fault Fracture Zone
## 4 Analysis of Synchronous Grouting Parameters
### Water Cover Height  
In order to further study the impact of synchronous grouting on the rock and soil mass in fault fracture zones under high burial depth and high water pressure conditions, parameter analysis was conducted on the overlying water conditions. The grouting pressure is 450 kPa, and the grouting filling coefficient is 100%. With the grouting parameters unchanged, different water head heights of 25 m, 30 m, 35 m, 40 m and no groundwater on the tunnel top surface are selected for analysis.  
Figure 26 shows the settlement variation curve of tunnels with different water cover depths. It can be seen that the influence of water depth factors on the fault fracture zone area and the original rock area is significantly different. The settlement effect in the original rock area is relatively small, while in the fault fracture zone area, as the water pressure condition increases, the settlement amount has a significant impact. When there is no groundwater, the settlement of rock and soil is significantly lower than when there is water pressure. Therefore, in the formation of fault fracture zones, if the overlying water pressure is too high, it may lead to excessive settlement exceeding the warning. The Chinese meaning of the black legend in the figure is 'no groundwater'.  
Figure 24: Tunnel top settlement curve.  
Figure 25: Maximum settlement variation under different grouting quantities.  
Select monitoring points in ordinary surrounding rock and fault fracture zones to analyze the pore pressure caused by synchronous grouting during shield tunneling. Study the variation of pore pressure under different water cover conditions with the same grouting parameters unchanged. As shown in Figures 27-29, under different water head heights, the grouting pressure of 450 kPa has a significant impact on the variation of pore pressure.  
Figure 28: Variation curve of pore pressure at ordinary surrounding rock monitoring points.  
Figure 26: Top settlement curve of tunnels along the line.  
Figure 27: Maximum settlement variation at different water cover depths.  
When the cutter head of the shield tunneling machine is heading towards the monitoring point, the initial hole pressure value gradually approaches the mud pressure value of the face. When the shield tail reaches the monitoring section, under different water cover depths, the hole pressure value of the monitoring point rapidly increases due to the grouting pressure, and the synchronous grouting pressure value towards the shield tail is close, and the influence becomes more obvious when the water cover depth is low, which is shown in Figure 30.  
Therefore, synchronous grouting during shield tunneling is the main reason for the changes in pore pressure of surrounding rock and soil, and the setting of grouting pressure needs to be further matched with the depth of overlying water to reduce disturbance to the formation structure. When grouting in the induced crack zone area, the influence of pore pressure is higher than that of ordinary surrounding rock and fractured zone, but the influence range is limited. After the shield tail leaves the monitoring point for 7 m, the pore pressure basically returns to the initial pore pressure.