# Study on the Effect of Anchor Cable Prestress Loss on Foundation Stability
## 3 Numerical Simulation
### Analysis of Numerical Simulation Results  
#### 3.4.1 Influence of Prestress Loss Rate on Formation Settlement  
The vertical displacement cloud map of the rock and soil mass in the middle section of the model after the completion of foundation pit excavation is extracted, as shown in Figure 4. Due to the great difference between the strength of the bedrock in the soil-rock composite formation and the upper soil layer, the settlement of rock and soil mass mainly  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Step** & **Working Condition Setting** & **Excavation Depth** \\ \hline
1 & Construction of bored pile and water curtain & 0 m \\
2 & The first floor is excavated for concrete support & 3.3 m \\
3 & The second floor is excavated for the first anchor cable & 6.8 m \\
4 & The third floor is excavated for the second anchor cable & 10.3 m \\
5 & The fourth floor is excavated for the third anchor cable & 14.3 m \\
6 & The fifth floor is excavated for the fourth anchor cable & 18.3 m \\
7 & The sixth floor is excavated to the bottom of the foundation pit & 22 m \\ \hline \hline \end{tabular}
\end{table}
Table 6: Calculation condition table.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Structural Members of the Foundation Pit** & **Density (kg/m\({}^{3}\))** & **Elasticity Modulus (MPa)** & **Poisson Ratio (-)** \\ \hline concrete inner support (C35) & 2600 & \(3.15\times 10^{4}\) & 0.2 \\ bored pile (C35) & 2600 & \(3.15\times 10^{4}\) & 0.2 \\ Shotcrete (C20) & 2500 & \(2\times 10^{4}\) & 0.25 \\ water curtain (P.O.42.5) & 2000 & 450 & 0.3 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Calculation parameters of the component model.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Number** & **Type** & **Elasticity** & **Cross-** & **Tensile** & **Bond of** & **Friction** & **Stiffness of** & **Outer** \\  & **Modulus** & **Sectional** & **Strength** & **Cement** & **Angle of** & **Cement** & **Pasté** & **Cement** \\  & **(MPa)** & **Area (m\({}^{2}\))** & **(MPa)** & **Pasté (kN/m)** & **Pasté (\({}^{5}\))** & **(MPa)** & **Pasté (m)** & **Pasté (m)** \\ \hline MS1 & Free section & & \(6.95\times 10^{-4}\) & & / & / & / & / \\  & Anchor & & \(6.95\times 10^{-4}\) & & 102 & 28 & 512 & 0.471 \\ MS2 & Free section & & \(8.34\times 10^{-4}\) & & / & / & / & / \\  & Anchor & & \(8.34\times 10^{-4}\) & & 100 & 28 & 570 & 0.471 \\  & section & \(2.05\times 10^{5}\) & \(6.95\times 10^{-4}\) & 1320 & / & / & / & / \\ MS3 & Anchor & & \(6.95\times 10^{-4}\) & & 102 & 28 & 512 & 0.471 \\  & section & & \(5.56\times 10^{-4}\) & & / & / & / & / \\ MS4 & Anchor & & \(5.56\times 10^{-4}\) & & 105 & 28 & 450 & 0.471 \\  & section & & \(5.56\times 10^{-4}\) & & 105 & 28 & 450 & 0.471 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Calculation parameters of the prestressed anchor cable.  
occurs in the depth of the soil layer within 10 m, and the maximum settlement gradually increases with the increase in the prestress loss rate. There is no obvious difference in the vertical displacement of the lower strata, and the uplift of the pit bottom is basically the same.  
The maximum settlement value of the rock and soil mass under different excavation depths and prestress loss rates is shown in Figure 5. When the excavation depth is shallow, the formation settlement value is lower, and the prestress loss rate is less affected. When the excavation reaches the rock layer (step 5, depth 10.3 m), the maximum settlement of the rock mass increases obviously, and the settlement speed increases gradually with the gradual increase in the excavation depth. The maximum settlement value increases linearly with the increase in prestress loss rate in deep rock stratum excavation. When excavating to the bottom of the pit, the maximum settlement value (4.07 mm) when the prestress loss rate is 40% increases by about 23% compared with the condition without prestress loss (3.31 mm). The prestressed loss significantly reduces the restraint effect of the supporting structure on the rock and soil outside the pit.