# 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
Additionally, the side friction of piles in the negative friction zone shows little difference under various loads. As the depth increases (beyond 2 m), the side friction of piles gradually becomes positive, entering the positive friction zone. In the positive friction zone, the side friction of piles shows significant differences under different loads and increases with increasing load. The interface between the negative and positive friction zones is called the neutral plane of the pile-soil interface. This plane is the critical location where the side friction of piles transitions from negative to positive. Figure 11b illustrates the distribution of the side friction of piles for permeable and impermeable piles under three different loading conditions. The figure shows that, for both pile types, the side friction of piles is higher at the pile head and pile toe (in opposite directions) and relatively lower in the middle part of the pile. The difference in side friction of piles between permeable and impermeable piles is slight in the negative friction  
Figure 11: Side friction of the piles of the pervious concrete piles: (**a**) distribution of side friction in pervious concrete piles; (**b**) comparison of the side friction of the piles. zone. However, in the positive friction zone, there is a significant difference in the side friction of piles between the two piles, with permeable piles exhibiting higher values than impermeable piles. Moreover, as the load increases, the difference in side friction of piles between permeable and impermeable piles becomes larger. When the load increases from 100 kPa to 300 kPa, the difference in the side friction of piles rises from 0.925 to 2.3, an increase of 148.65%. This result indicates that permeable concrete piles can more effectively transfer and distribute lateral loads under higher loads, thereby exhibiting better side friction of the piles. Figures 12 and 13 show the pile-soil stress ratio and pile load-sharing ratio for the two types of composite foundations under different loading conditions. As seen in Figures 12 and 13, when the load increases from 50 kPa to 150 kPa, both the pile-soil stress ratio and the pile load-sharing ratio show a clear upward trend. This indicates that the pile takes on a more significant proportion of the load in the initial stage. However, both ratios decline as the load rises from 150 kPa to 300 kPa. This suggests that the bearing capacity of the soil surrounding the pile increases, and the soil begins to take on more of the load. Specifically, under a load of 150 kPa, the pile-soil stress ratio and pile load-sharing ratio for the permeable concrete pile composite foundation reach their maximum values at 19.03 and 0.441, respectively. In contrast, under a load of 300 kPa, these ratios drop to 17.13 and 0.409, respectively. This change shows that the pile bears a larger share of the  
Figure 12: Comparison of pile–soil stress ratios. Figure 13: Comparison of pile load-sharing ratios. load in the initial loading stage. As the soil consolidates and its bearing capacity increases, the foundation soil gradually takes on more of the load, decreasing the ratios. The ratios for permeable concrete piles are lower under higher loads compared with impermeable piles. This indicates that permeable piles effectively accelerate the consolidation of the soil, thereby enhancing the overall bearing capacity of the foundation.