*3.1. The Whole Measuring Process of Stress and Deformation of the Anti-Slide Pile*

Figure 11 illustrates the lateral displacement distribution of the test pile under different trapezoidal load levels, and the ordinate in Figure 12 represents the resultant force (*FT*) of the concentrated forces *F*1, *F*2, *F*3. The relationship curve between the pile top lateral displacement and the resultant force of trapezoidal load was extracted in Figure 12. It can be seen that the pile lateral displacement increased linearly along the pile length as trapezoidal load increases, and the deformation process of the cantilever anti-slide pile included three stages. In Stage I, the pile lateral displacement increased approximately proportionally with the resultant force of the trapezoidal thrust load (*FT*), but the rate of increase was relatively slow. In this stage, the cantilever anti-slide pile worked in full section, and the concrete and the steel bars in the tension area bore the tensile force together, both of which were in an elastic stage. When *FT* increased to 10.2 kN, the maximum lateral displacement at pile top was 1.75 mm, and the tensile area near the sliding surface of side A of the test pile first cracked (Figures 12 and 13a), which was named as the uncracked stage of the cantilever anti-slide pile. In Stage II, due to the concrete cracking in the tension area, the tensile force originally born by the concrete was gradually transferred to the tensile steel bars, and the cracks on side A, side B, and side D of the test pile gradually expanded and extended (Figures 12 and 13b,d). As the trapezoidal load increased, the tensile force at the cracking area was basically born by the tensile steel bars. In this stage, the lateral displacement of the pile increases more obviously due to the presence of cracks, and the lateral displacement at pile top increases in a non-proportional manner with *FT*. When *FT* increased to 36.6 kN, the maximum lateral displacement at pile top was 17.5 mm, and the tensile steel bars began to yield. Since then, the maximum lateral displacement at the pile top increased sharply, which was named as the crack emerging and developing stage of cantilever anti-slide pile. In Stage III, when *FT* gradually increased to 40.2 kN, the concrete strain in the compression area reached the ultimate compressive strain, and the concrete in the compression area crushed and bulged (Figures 12 and 13c). The trapezoidal thrust load gradually rebounded, the maximum lateral displacement at pile top was 63.7 mm, and the anti-slide pile subsequently failed (Figures 12 and 13e), which was named as the steel bar yielding-failing stage of cantilever anti-slide pile.

**Figure 11.** Displacement distributions along the test pile.

Further investigation on the cracks and failure characteristics of the test pile indicated that the initial crack was located 3 cm above the sliding surface of side A. The crack was a transverse crack parallel to the pile width, and its width was about 0.1 mm. When the anti-slide pile entered Stage II, inclined cracks began to appear on side B and side D of the test pile and extended to the compression area (Figure 13b,d). At the same time, the number and width of transverse cracks on side A of the test pile gradually increased, the number of cracks reached 5 and the maximum transverse crack width was about 8 mm (Figure 13a). When the trapezoidal load increased to the ultimate bearing capacity of the test pile, the inclined cracks on side B and side D of the test pile gradually penetrated into the compression area, and the concrete of side C of the test pile showed compression-tension cracks and bulged outward (Figure 13c), resulting in bending failure (Figure 13e). The above phenomena indicate that the cantilever anti-slide pile under trapezoidal load sustains typical plastic failure and ductile failure characteristics, and belongs to under-reinforced beam damage. The cracking load and yield load of the test pile were 25.37% and 91.04% of the failure load, and the cracks were distributed within about 10 cm (0.09 times the pile length) above and below the sliding surface.

**Figure 12.** Variation curve of the thrust load with the pile top displacement.

**Figure 13.** Crack distributions along the test pile. (**a**) Side A; (**b**) Side B; (**c**) Side C; (**d**) Side D; (**e**) Pile.

Figure 14 illustrates the strain distributions along different heights of concrete in side B of test pile under various loads. Due to the wide crack after the cracking of the anti-slide pile section, some strains on the CSG-2 row could not be accurately collected. The conclusion could be drawn that the concrete strains at different heights of two sections of the test pile were basically proportional to the distances from the points to the neutral axis when the load was fixed, and the concrete strains were linear, which indicated that the plane section assumption was available.
