## 4 Analysis of Test Results
### Analysis of Internal Forces of Anchors
\[\tau=\frac{(\varepsilon_{j}-\varepsilon_{j+1})EA_{\text{s}}}{\pi d\Delta \varsigma} \tag{2}\]  
where \(E\) is the modulus of elasticity of the reinforcement, \(A_{\text{s}}\) is the cross-sectional area of the reinforcement, \(\varepsilon_{i}\) is the strain value of any section \(i\), \(\Delta\varsigma\) is the distance between two measurement points and \(d\) is the diameter of the anchor solid. Based on Equation (2), the shear stress distribution of anchor M2-5 under excavation conditions was shown in Figure 12. What can be seen is that, for the tension type anchor, the shear stress distribution of the anchor solid shows a trend of increasing first and then decreasing. It reaches the peak after a certain distance from the beginning of the anchorage section, and then starts to decrease and tends towards zero at the end of the anchorage section. Therefore, for tension anchors, the anchor solid shear stress is mainly borne by the first half of the anchorage section, and the second half of the anchorage section takes up a relatively small proportion. This shows that the anchor solid is not as long as possible, but that there is an optimal anchorage length. After the anchorage section exceeds a certain length, the shear stress provided by the anchor solid is very limited, which is not conducive to the conservation of resources and the sustainable development of the foundation pit project. Due to the group anchor effect between soil anchors, the tensioning of adjacent anchors affects the internal force of each anchor. The following is an example of anchor M1-3; the effect of tensioning the anchors adjacent to anchor M1-3 on the internal force of M1-3 is investigated, and the results are shown in Figure 13. In order to facilitate visual analysis of the loss of axial force of anchor M1-3, the internal force of anchor M1-3 during tensioning of adjacent anchors is normalized and expressed as the relative value of its axial force. The initial value of the axial force of anchor M1-3 after treatment was 1. The anchor M1-3 was tensioned first, followed by the adjacent anchors in sequence. When the anchors were tensioned according to the sequence in Figure 13a, it can be seen that the axial force of the target anchor M1-3 lost 39% when the anchor M1-2 to the left of M1-3 was tensioned, and the axial force of M1-3 lost another 32% when the anchor M1-4 to its right was tensioned. This was only 29% of its initial value. When tensioned according to the sequence shown in  
Figure 11: Axial force distribution of M2-5 anchors under excavation conditions. Figure 13b, the axial force of anchor M1-3 is 74% and 45% of its initial value, respectively. When tensioned in the order shown in Figure 13c, the axial forces of anchors M1-3 are 82% and 62% of their initial values, respectively. It can be seen that the tensioning sequence of anchors has a large effect on the axial force of anchors. When the anchors were tensioned sequentially, the loss of axial force of the target anchors was more obvious. The axial force loss of the target anchor is significantly reduced if tensioning is done at a certain number of intervals. The greater the distance between tensions, the smaller the axial force loss of the target anchor; for the inverse, the greater is the axial force loss. Therefore, the tensioning sequence of anchors in actual construction can follow the principle of a certain distance between tensions in order to reduce the loss of axial force of anchors during the construction process, which leads to the decrease of anchoring effect of anchors. This can effectively avoid the situation that the axial force loss of anchor is too large to control the deformation of the foundation pit and reduce the potential safety of the foundation pit. Figure 12: Shear stress distribution of M2-5 anchors under excavation conditions. Figure 13: Effect of adjacent anchor tensioned on the axial force of anchor M1-3. (**a**) Sequential tensioning; (**b**) Tensioning at intervals of one hole; (**c**) Tensioning at intervals of two hole.