# Study on the Bearing Characteristics of Composite Foundations with Permeable Concrete Piles
## 4 Results and Discussions  
### Comparison of Bearing Characteristics of Permeable and Impermeable Piles  
Figure 9 shows the settlement curves of the two types of composite foundations under different loading conditions. In the initial loading stage, the difference in settlement between the permeable concrete pile and the impermeable concrete pile composite foundations is slight. The load-settlement curves show an approximately linear relationship. As the load increases gradually, the difference in settlement between the two foundations becomes larger. The settlement of the permeable concrete pile composite foundation is significantly less than that of the impermeable pile composite foundation. When the load reaches 300 kPa, the settlement of the impermeable concrete pile composite foundation is 24.91 mm, while the settlement of the permeable concrete pile composite foundation is only 12.74 mm. This represents a 50.13% reduction in settlement compared to the impermeable pile. This is because the interconnected pores within the permeable concrete piles form vertical drainage channels. These channels enhance radial and vertical seepage in the foundation, accelerating consolidation and reducing settlement. Figure 10a illustrates axial force distribution in permeable concrete piles under different loads. As the foundation depth increases, the axial force in the pile initially increases  
Figure 8: Pore pressure contour map of pile composite foundation (Pa): (a) head differences in radial and vertical directions; (b) hydraulic head difference in the vertical direction. Figure 9: Load–settlement curve of composite foundation. and then decreases. Specifically, the axial force increases at depths less than 2.7 m and gradually decreases at depths greater than 2.7 m. Comparing the axial forces at the same depth, it is observed that as the load increases, the axial force in the upper part of the pile significantly rises. In contrast, the increase in the lower part is relatively small. This is due to the increasing influence of the side friction of piles with depth. For example, at a load of 50 kPa, the top axial force is 23.16 kN, and the bottom axial force is 18.11 kN. When the load reaches 300 kPa, the top axial force increases to 96.37 kN, while the bottom axial force is 35.71 kN. This indicates that as the load increases, the effect of side friction of piles becomes more pronounced, leading to a better attenuation of axial force. This phenomenon reflects the varying influence of the side friction of piles on axial force distribution at different loading stages. Figure 10b shows the axial force distribution of permeable and impermeable concrete piles under three different loading conditions. The figure indicates that the difference in top axial force between the two types of piles is relatively tiny. However, this difference increases with depth. This suggests that the axial force attenuation in the depth direction is more significant for permeable piles than impermeable piles. This is attributed to the porous structure of permeable piles, which facilitates soil drainage and consolidation, thereby effectively enhancing the pile's load-bearing capacity. Additionally, as the load increases, the difference in axial force between permeable and impermeable piles becomes  
Figure 10: Axial force in pervious concrete piles: (**a**) axial force distribution along the pervious concrete pile; (**b**) comparison of axial forces in piles. larger. This further highlights the structural advantages of permeable piles under different loading conditions. Figure 11a shows the distribution of side friction of piles of permeable concrete piles under different loads. The figure indicates that when the soil depth is less than 2 m, the side friction of the piles of the pile is negative. This occurs because, within this depth range, the settlement rate of the pile is lower than that of the surrounding soil. As a result, downward frictional resistance is generated between the pile and the soil, creating a negative friction zone.