## 5 Analysis of the Combined Load-Bearing Characteristics of Piles and Soil in Composite Foundations
### Discussion  
Composite foundations are essential in engineering applications, and understanding their bearing mechanisms is crucial for effective designs. In this study, we investigated the internal force diffusion mechanisms of friction piles and end-bearing piles to provide guidance for pile foundation designs. Additionally, we explored the calculation of additional forces in piles and inter-pile soil to inspire solutions for uneven settlement treatments in composite foundations. To compare the effects of different parameters on the combined bearing capacity of composite foundations, finite element numerical simulation methods were employed. Specifically, we analyzed the variations in the additional vertical forces in the depth direction of pile lengths for single piles, inter-pile soil, and all piles. We also investigated the load-sharing effects between piles and soil. In order to study the influence of various parameters on the additional vertical forces of all piles and soil within the composite foundation, the maximum ratio \(\lambda_{\text{t}}\) (pile top) and minimum ratio \(\lambda_{\text{b}}\) (pile bottom) of the additional vertical forces to the top load were compared under different conditions. The increase in the \(\Delta\lambda_{\text{t}}\) and \(\Delta\lambda_{\text{b}}\) ratios after changing the parameters is presented in Table 3.  
Figure 16: Variation in additional vertical forces along depth direction for all piles and inter-pile soil with a pile length of 20 m: (**a**) sum of additional vertical force on piles and inter-pile soil; (**b**) ratio of additional vertical forces on piles and inter-pile soil to upper load. It was observed that variation in the parameters had a limited impact on the maximum ratio \(\lambda_{\text{t}}\) of the additional vertical forces of piles and soil to the top load, with \(\Delta\lambda_{\text{t}}\) consistently within 2%. However, the impact on the minimum ratio \(\lambda_{\text{b}}\) was significant after changing the parameters, especially when switching from friction piles to end-bearing friction piles, where the increase in \(\Delta\lambda_{\text{b}}\) reached 133.277%. This further demonstrates the significant advantage of end-bearing piles in improving the bearing capacity of pile foundations in composite foundations. In summary, the ratios of piles and soil to the top load vary under different conditions and are influenced by multiple factors. Further numerical simulations or experimental studies are needed to deepen our understanding of how these factors affect the joint-bearing capacity performance of pile-soil systems in composite foundations, and to validate the data and trends in the table. Additionally, the optimization of pile design parameters can be explored to enhance the stability and bearing capacity of structures. In order to validate the effectiveness of the results obtained in this study, a comparison was made with the computational method presented in [7]. The comparison results are shown in Figure 17. In [7], a finite element analysis was employed to investigate the influence of the cushion layer, pile length, soil modulus, and pile spacing on foundation settlement and stress distribution. Therefore, the same research object and computational parameters as those in [7] were selected for comparison. However, unlike [7], this study considered the negative skin friction on the pile and the end-bearing effect. The comparison of the calculated results for the pile stress along the depth is shown in Figure 17, which indicates a close agreement between the variations in pile stress. The discrepancies observed can mainly be attributed to two factors:  
1. Element type: Ref. [7] employed 20-node solid elements, while this study used 8-node solid elements. The difference in the displacement interpolation functions between the two types of elements arose from the incomplete quadratic polynomial interpolation functions of the 20-node elements, leading to certain computational errors. 2.