## 3 Results and Discussion
### Analysis of the Effect of Different Embarknment Fill Loadings  
The effects of half and full width loading filling heights of 0.3 m, 0.6 m, 0.9 m, 1.2 m, and 1.5 m, and construction intervals of 2d, 7d, and 15d on the FOS of the composite roadbed with PHC pipe piles are shown in Figure 7, where 2d, 7d, and 15d indicate the time intervals between two fill constructions. Half and full width loading refers to scenarios where either half or the entire road width is filled, respectively, exploring the impact of loading uniformity on the roadbed response.  
From Figure 7, it can be seen that the FOS of the PHC pipe pile composite roadbed decreases continuously as the filling height increases from 0.3 m to 1.5 m with the same interval, both for half-width loading and full-width loading. The FOS under half-width  
Figure 6: Settlement cloud of a composite roadbed with different pile verticality values under a pile/soil load ratio of 7:3. Pile verticality is (**a**) 1\({}^{\circ}\), (**b**) 3\({}^{\circ}\), (**c**) 4\({}^{\circ}\), (**d**) 6\({}^{\circ}\), (**e**) 7\({}^{\circ}\), (**f**) 8\({}^{\circ}\).  
Figure 7: Effect of different embankment fill loading methods on the safety factor of PHC pipe pile composite roadbeds.  
and full-width loading, at intervals of 2d, decreased by 9.35% and 12.50%, respectively. Similarly, at intervals of 7d, the FOS decreased by 8.84% and 11.60%, respectively, and at intervals of 15d, the FOS decreased by 16.34% and 16.38%, respectively. When the loading interval was extended from 2d to 15d, the FOS of the composite roadbed gradually increased, indicating that an increase in filling rate leads to a decrease in the FOS. Therefore, the loading method (half width or full width), loading rate (interval time), and filling height have varying degrees of influence on the stability of PHC pipe pile composite roadbeds. Although a fast construction rate may save cost and time, it can compromise the FOS of the composite roadbed during the construction process. This is because the soil layers of each stratum may not be sufficiently consolidated, resulting in a reduced stability of the composite roadbed. Especially during the rainy season, the intrusion of rainwater can make the composite roadbed heavier and more prone to accidents such as sliding and collapsing.  
The settlement rate and consolidation degree of the soft soil layer can be affected by the filling rate. These factors, in turn, impact the strength of the soft soil layer. Therefore, it is crucial to determine a reasonable construction interval in order to enhance the stability and safety of the composite roadbed. A smaller filling rate results in a longer settlement and consolidation time, which effectively compacts the soft soil and improves its strength to some extent. This helps prevent excessive overall settlement of the roadbed, which could affect the slope's stability. When piling and filling soft soil in a composite roadbed, it is important to consider that the strength of the soft soil layer may not be sufficient to bear excessive loads. Therefore, the initial discharge height should not be too high. As the soft soil layer settles and consolidates over time, its strength improves, allowing for an increase in the subsequent filling height. Considering the actual construction process, construction cost, and other factors, a slower loading rate is not necessarily better for PHC pipe pile composite roadbeds. A single filling height of approximately 0.6-0.9 m is relatively optimal.