## 3 Experimental Results
### Horizontal Deformations  
Figure 9 presents the deformation shapes of nine specimens. As Figure 9 shows, all the specimens had a flexural deformation along the buried depth, which indicates that these specimens were ductile piles. The maximum deformation was at the top of all the specimens and deformation reduced to zero gradually at 10.3 D of the buried depth (around 1.6 m) for the CP-1, CP-2 and CP-4 specimens, 11.6 D of the buried depth (around 1.8 m) for the CP-3, RP-8 and HP-9 specimens, and 13.5 D of the buried depth (around 2.1 m) for CP-5, PC-6 and PC-7, respectively. The inflection points were shifted to the deeper buried depth with the increase of displacement loadings. The inflection points were located at the pile depth of 1.5 m to 2.1 m as shown in Figure 10. The specimens had reserved deformations below the inflection point and beyond 2.5 m buried depth the deformation was negligible.  
From Figure 9 it can be seen that the CP-3, CP-5 and PC-7 specimens had a better deformation capacity as the displacement loadings increased, which also shows that the larger reinforcement ratio, buried pile depth and prestressing level can significantly increase the deformation capability of pile foundations. In addition, the HP-9 specimen experienced the largest negative deformation, which was -2.5 mm. The CP-3 and RP-8 specimens' negative deformations were -1.51 mm and -1.53 mm, respectively. The H-shaped steel pile had better plastic deformation and ductility as compared to the reinforced concrete piles. The rectangular RP-8 specimen had a better deformation capacity as compared to the circular CP-2 specimen.  
As shown in Figure 10, the inflection points of the CP-1 to CP-5 and PC-6 to PC-7 specimens shifted downward with the increase of the reinforcement ratio, buried pile depth and prestressing level. The depths of the inflection point of the CP-3, RP-8 and HP-9 specimens were the same. The PHC specimens with a lower prestressed level had the same inflection point depth. As the reinforcement ratio of the piles increased, the inflection point depths also increased. The aforementioned analyses indicated that the reinforcement ratio, buried pile depth, prestressed level and cross-section size have significant effect on the depth of the inflection point of the pile. Therefore, the flexural and cyclic deformation capacity of the pile can be improved by increasing the reinforcement ratio, buried pile depth, prestressed level and cross-section size.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Specimen** & **CP-1** & **CP-2** & **CP-3** & **CP-4** & **CP-5** & **PC-6** & **PC-7** \\ \hline \(L_{ci}\) & 3.5 D & 3.6 D & 5.4 D & 3.4 D & 4.3 D & 4.4 D & 4.6 D \\ \(L_{ci}\)/\(L_{c1}\) & 100\% & 103\% & 154\% & 97\% & 123\% & 126\% & 131\% \\ \hline
**Specimen** & **RP-8** & **HP-9** & **PHC-1 [28]** & **PHC-2 [28]** & **PHC-3 [28]** & **PHC-4 [28]** & \\ \hline \(L_{ci}\) & 6.2 D & – & 4.5 D & 4.2 D & 5.2 D & 7.7 D & \\ \(L_{ci}\)/\(L_{c1}\) & 177\% & – & 129\% & 120\% & 149\% & 220\% & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of concrete crushing locations for all the specimens.  
Figure 9: Deformed shapes of all specimens. (**a**) The effect of different reinforcement ratio. (**b**) The effect of different buried pile depth. (**c**) The effect of different prestressing level.