## 3 Comparative Analysis of Working Performance of Pile-Raft System
### Results and Discussion
#### 3.3.2 Performance of Piles  
Based on the models in Schemes 1, 2, and 3, the embedded pile element was used to simulate the pile, and the axial force and lateral friction distribution of P1-P4 (shown in Figure 4) were analyzed, as shown in Figures 13 and 14.  
Figure 13: Distribution of the axial force of the pile: (**a**) raft + bored pile; (**b**) raft + cushion + bored pile; (**c**) raft + cushion + CFG pile.  
It is clear from Figure 13 that the distributions of the axial forces of the pile in the three simulation schemes were different. In Scheme 1, the axial force of the pile was larger in the shallow part of the pile and smaller in the deep part, which was approximately linear with depth. The axial force of the pile in Scheme 2 was represented by a broken line with depth, and the axial force in the middle of the pile was large and the axial force at both ends was small. In Scheme 3, the distribution of the axial force of the pile had an approximately arched shape, the axial force was larger in a certain range of the middle and upper parts of the length of the pile, and the axial force was approximately linear in the range of nearly one quarter of its length to the top or bottom of the pile. This result was consistent with the results of the analysis by [PERSON] et al. [21].  
By comparing the axial force of the pile in different positions (P1, P2, P3, and P4), it is clear that the distribution of the axial forces of the four piles in Scheme 1 was roughly the same, that of the central pile (P3) was slightly different from the side piles (P2 and P4) and the angular pile (P1). The axial force was larger from the top of the pile to a certain depth, and then decreased linearly with increasing depth. In Scheme 2, the distributions of the axial forces of P1 and P4 were similar, and those of P2 and P3 were similar, while the axial forces of P1 and P4 were higher than those of P2 and P3. In Scheme 3, the axial force of P1 was the largest and that of P3 was the smallest, while the axial forces of P2 and P4 were between those of the former two piles and had similar distributions.  
Figure 14 shows the distribution of the lateral friction of the pile in the abovementioned three simulation schemes. The lateral friction of the pile in Scheme 1 was significantly different from those of Schemes 2 and 3 with the cushion, and there was no negative friction along the length of the pile in Scheme 1 because of the synchronous subsidence of the bored pile and raft when they were rigidly connected. Because there was a certain thickness of the cushion on top of the pile in Schemes 2 and 3, the cushion was compressed and sunken due to the load applied by the raft, the top of the pile was pierced into the cushion, the soil between the piles was compressed and deformed under pressure from the cushion, and the displacement of the pile was downward. Therefore, negative friction appeared in a certain range below the top of the pile in Schemes 2 and 3, and then became positive as depth increased. It can be concluded that the presence of the cushion between the top of pile and the raft determines the differences in the mechanism of the pile-soil-raft interaction [21]. Moreover, the depth of distribution of the negative lateral friction of the pile in Scheme 2 was close to 6 m, which was approximately two times the distribution of the negative lateral friction in Scheme 3 in terms of depth. This indicates that the relative displacement between the pile and soil in the foundation stabilized  
Figure 14: Lateral frictional distribution of the pile: (**a**) raft + bored pile; (**b**) raft + cushion + bored pile; (**c**) raft + cushion + CFG pile.  
using the CFG pile with high stiffness was larger than that of the CFG pile with relatively low stiffness. From the point of view of the pile-soil-cushion-raft interaction mechanism, the above reasons also explain why the raft settlement in Scheme 2 was larger.