# Enlarged Head Pressure-Dispersed Anchor Cable for Foundation Pit Engineering Purposes
## 4 Numerical Simulation Analysis of the Anchor-Cable Support System
### Results and Analysis of the Numerical Simulation  
#### 4.2.1 Support Effect of the Enlarged Head Pressure-Dispersed Anchor Cable on Foundation Pit  
Two pumping wells were set inside the foundation pit and at the edge of the foundation pit, with a depth of 18 m. At the beginning of precipitation, the pore pressure around \begin{table}
\begin{tabular}{c c c} \hline \hline
**Working** & **Calculation Method** & **Condition Description** \\ \hline \multirow{3}{*}{\(1\)} & \multirow{3}{*}{Fluid–structure coupling} & Pumping wells and drainage wells with depths of 18 m were set at x = 2 m and \\  & & x = \(-\)25 m, respectively. \\  & & In the range of 3–4 m depth, some soils were in the waterproof layer. Un-drained \\  & & water was simulated by zone GRIDPOINT fix pore pressure 0 command. \\ \hline
2 & Mechanical calculation & Slope was down while excavating to 3 m below the ground level. \\ \hline
3 & Mechanical calculation & Construction of support pile, water-stop curtain, and top beam. \\ \hline
4 & Fluid–structure coupling & Pumping wells continue to pump water, and open drainage treatment was carried out \\  & & within the depth of 4.8–5.8 m. \\ \hline
5 & Mechanical calculation & Excavation to 4.8 m below ground level. \\ \hline
6 & Mechanical calculation & At a depth of 4.3 m, the lumbar girder and anchor cable were constructed and \\  & & prestressed. \\ \hline
7 & Fluid–structure coupling & Pumping wells continued to pump water, and the depth was within the range of \\  & & 7.8–8.8 m. Open drainage treatment was carried out. \\ \hline
8 & Mechanical calculation & Excavation to 7.8 m below ground level. \\ \hline
9 & Mechanical calculation & At a depth of 7.3 m, the lumbar girder and anchor cable were constructed and \\  & & prestressed. \\ \hline
10 & Fluid–structure coupling & Pumping wells continued to pump water, and the depth was within the range of \\  & & 9.52–10.52 m. Open drainage treatment was carried out. \\ \hline
11 & Mechanical calculation & Excavation to 9.52 m below ground level. \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Foundation pit working conditions. Figure 17: The boundary conditions for flow and displacements. the pumping well obviously decreased, as shown in Figure 18. Because the third and fourth layers of soil were silty clay layers, the permeability coefficient was very small, forming a natural aquifer, which could only be drained out by the open drainage during construction. After precipitation, the water in the aquifer was not discharged in time, forming a clear boundary, as shown in Figure 19. It can be clearly seen from the stress contour diagram of pore water pressure that the pore water pressure dropped to 0 within a meter below the excavation surface. It was observed that the water pressure in the range of seepage radius of the pumping well decreased significantly. The surface settlement around the foundation pit under different working conditions is shown in Figure 20. Working Conditions 4 and 7 show that the dewatering process of the foundation pit increased the surface settlement near the edge of the foundation pit, and the influence effect was up to 23 mm. Due to the Mohr-Coulomb constitutive model, the elastic deformation and plastic deformation of the soil coexisted after an in situ stress balance. After excavation under working Conditions 5 and 8, the soil around the foundation pit suddenly lost its compressive force, and the elastic deformation of soil was released. It is shown that the ground near the edge of the foundation pit rebounded. On the bottom surface of the foundation pit excavation, the self-weight stress in the vertical direction was lost, resulting in a small increment in the vertical displacement. Figure 19: Final pore water pressure distribution. Figure 18: Initial pore water pressure distribution.