# Model Test of Stress and Displacement of Recyclable Anchor Rod Support Structure
## 3 Test Results
### Analysis of Bending Moment of Supporting Pile  
In the process of excavation, the central pile was selected to analyze its bending moment, and the measured strain data were obtained according to Formulas (10) and (11).  
\[M=EI(\varepsilon_{+}+\varepsilon_{-})/h \tag{10}\]  
\[I=\pi\Big{(}D^{4}-d^{4}\Big{)}/64 \tag{11}\]  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Project Condition** & **Type** & **Anchor Rod** & **Depth (cm)** \\ \hline
\begin{tabular}{c} Excavation and laying of an \\ anchor rod \\ \end{tabular} & Anchor rod 1 & 10.00 \\
2 &
\begin{tabular}{c} Excavation \\ \end{tabular} & & 20.00 \\
3 &
\begin{tabular}{c} Excavation and laying of an \\ anchor rod \\ \end{tabular} & Anchor rod 2 & 30.00 \\
4 &
\begin{tabular}{c} Excavation \\ \end{tabular} & & 40.00 \\
5 &
\begin{tabular}{c} Excavation \\ \end{tabular} & & 50.00 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Parameter table of project conditions.  
Figure 4: Layout of measuring points.  
where \(M\) indicates the pile's bending moment (N-m); \(E\) refers to the elastic modulus of the support pile (Pa); \(\epsilon_{+}\), \(\epsilon_{-}\) denote the strain data; \(h\) represents the strain gauge measurement point spacing (m); \(D\), \(d\) signify the outer diameter and inner diameter of the support pile (m), respectively.  
The bending moment variation curve of the central pile was obtained by processing the data, as presented in Figure 5:  
Figure 5 suggests that the upper part of the supporting pile with the recyclable anchor rod support structure mainly bears a positive bending moment, while the lower part mainly bears a negative bending moment. The overall supporting pile presents a trend of a large middle bending moment and a small bending moment on both sides. With the deepening of excavation, the position of the reverse bending point of the supporting pile gradually declines. The overall supporting pile is a positive bending moment when the excavation reaches the design depth. The maximum bending moment reaches 0.56 N.  
As a retaining structure, the retaining pile primarily withstands the external, active earth pressure exerted on the foundation pit. The anchor body transfers the load to the deep soil layer, thereby reducing the displacement and internal forces acting on the supporting pile and maintaining the stability of the foundation pit. At the early stage of excavation, the bending moment of the supporting pile changes slightly, owing to the small excavation depth. The bending moment value of the supporting pile increases with the increase in the excavation depth. The bending moment of the supporting pile decreases slightly near 10 cm. The reason for this phenomenon is that the prestressed anchor rod was installed at 10 cm. Under the action of the earthwork unloading, the prestressed anchor rod plays its role and generates the tension resisting the earth pressure behind the supporting pile, and the anchoring section of the recoverable anchor transmits the force into the soil and shares the effect of part of the earth pressure on the supporting pile, restricting the bending moment and deformation of the supporting pile and restricting the bending moment and deformation of the supporting pile. In the process of excavation, the maximum positive bending moment and a minimum negative bending moment of the supporting pile increased gradually, and the maximum bending moment value of the supporting pile was about 1/3 of the length of the pile. Moreover, the position of the maximum bending moment value of the supporting pile gradually declined with the deepening of the excavation. Two anchor rods were set in this supporting structure, equivalent to adding two elastic fulminations on the supporting pile. Therefore, the supporting pile exhibited  
Figure 5: Bending moment curves of supporting pile.  
an overall trend of an inverted S-shape change under the action of soil stress and the prestressed anchor rod.