## 3 Results Analysis and Discussion  
### Pile Strain and Bending Moment  
During the test process, the strain of the steel-pipe pile body was monitored through the resistance strain gauge pasted on the pile body. The strains of No. 2 pile body, measured three times after the foundation pit excavation was completed, were selected for the analysis, as displayed in Figures 14 and 15. A positive value of the pile body strains indicates that the monitoring point is under a tensile state, whereas a negative value indicates that the monitoring point is under a compressive state. The pile body experiences positive bending if its rear side is under a tensile force while its front side is under a compressive force. By contrast, the pile body withstands negative bending if its rear side is under a compressive force while its front side is under a tensile force. Figure 14 presents that, after the foundation pit excavation, a strain change at the front side of the pile body gradually stabilized with time. The front side of the pile body above the undersurface of the foundation pit was mainly under the tensile state. The maximum tensile strain was 275 \(\upmu\varepsilon\), which occurred at 4 m below the ground surface. At the position below the undersurface of the foundation pit, the front side of the pile body was under the compressive state. The maximum compressive strain was \(-\)75 \(\upmu\varepsilon\), which occurred at 1.5 m below the undersurface of the foundation pit. Near the undersurface, zero-strain points appeared at the front side of the pile body. The strain value at the front side of the pile body was greater above the undersurface of the foundation pit than below. Figure 14: The strain at the front side of the pile body. Figure 15: The strain at the rear side of the pile body. Through an analysis of the rear-side strain of the pile body, the following conclusions were drawn. After completing the foundation pit excavation, the tensile region at the rear side of the pile body was mainly distributed below the undersurface of the foundation pit. However, the compressive region at the rear side of the pile body was mainly distributed above the undersurface of the pit. The maximum compressive strain at the rear side of the pile body occurred at 4 m below the ground surface, whereas the maximum tensile strain occurred at 1.5 m below the undersurface of the foundation pit. Zero strain at the rear side of the pile body occurred near the undersurface of the foundation pit. The strain value at the rear side of the pile body was smaller below the undersurface of the foundation pit than above. Through a comparative analysis of the front-side and rear-side strains of No. 2 pile body, the front side was under the tensile state above the undersurface of the foundation pit, whereas its rear side was under the compressive state. The pile body experienced negative bending, and the maximum bending deformation of the pile body occurred at 0.62 \(H\) (\(H\) is the depth of the foundation pit excavation) below the ground surface. This result was due to the fact that the supporting structure underwent bending deformation toward the foundation pit under the action of a constraining effect of the cap beam and the active earth pressure behind the supporting structure. Below the undersurface of the foundation pit, the front side of the pile body was under the compressive state, whereas its rear side was under the tensile state. The pile body experienced positive bending, and its maximum bending deformation occurred at 0.23 \(H\) below the undersurface of the foundation pit. The front- side and rear-side strain curves of the pile body were relatively symmetrical.