# Model Test of Stress and Displacement of Recyclable Anchor Rod Support Structure
## 3 Test Results
### Horizontal Displacement of Pile Top  
The changes in the pile top horizontal displacement during excavation are shown in Figure 6.  
It can be observed in Figure 6 that the horizontal displacement of the pile top of the supporting structure using recycled anchor rods and the common pile-anchor rod support structure increases with the gradual excavation of the deep foundation pit. In the process of excavation, the displacement development of both structures is consistent.  
The horizontal displacement of the pile top gradually increases. At the early stage of excavation, soil stress in the excavation area is redistributed due to the unloading of the soil mass in the excavation area, and active earth pressure is generated on the unexcavated side. Since the excavation depth is small in the early stage of excavation, the range of soil stress variation is not large, resulting in a small range of the horizontal displacement of the pile top in the early stage of excavation. With the continuous excavation of the foundation pit, the active earth pressure on the unexcavated side continuously increases, and the development of pile top horizontal displacement develops a positive correlation with the excavation depth. Furthermore, the change range of the horizontal displacement of the top of the supporting pile decreases when the excavation reaches the design depth. This is in that after the excavation reaches the design depth, the soil unloading is completed, the stress distribution tends to be stable, and the horizontal displacement of the top of the supporting pile begins to stabilize. The horizontal displacement of the top of the supporting pile reaches the maximum in project condition 5, with a maximum displacement of 0.15 mm.  
Figure 7 exhibits the rates of change in the horizontal displacement of the pile top of the ordinary pile-anchor rod support structure and the support structure using recyclable anchor rods with the project condition. As suggested in Figure 7, the first recyclable anchor rod is laid at the excavation to 10 cm. After the excavation of the soil mass in the first layer, the anchor rod is prestressed by tightening the nut at the end of the excavation. The horizontal displacement of the pile top in project condition 1 is less than that in other project conditions. The second layer of the rock anchor rod does not play a role when the second layer of soil is excavated to the second layer of soil. Thus, the horizontal displacement of the pile top in project condition 2 is larger, and the growth rate is faster than that in project condition 1. Afterward, the foundation pit continues to excavate. When the excavation reaches 30 cm, the prestress is applied to the second layer of the rock anchor rod, and the second layer of the rock anchor rod plays a role in resisting part of the active earth pressure.  
Figure 6: Horizontal displacement variation curve of pile top.  
The growth range of the pile top horizontal displacement in project conditions 1 and 3, corresponding to the effect of the anchor rod, is smaller than that in other project conditions. Therefore, the pile-anchor rod support structure with a recyclable anchor rod can effectively limit horizontal displacement during the excavation of the foundation pit.