Numerical Study of the Long-Term Settlement of Screw–Shaft Pile Reinforced Subgrade Under Cyclic Train Load

High-speed railways (HSR) set strict limits on subgrade settlement. Excessive settlement, especially the differential settlement at the transition part between viaduct lines and embankment lines, could lead to discomfort on HSR trains and even accidents like derailments. Thus, proper ground treatment measures are inevitably needed. Screw-shaft pile reinforced subgrade was adopted in the transition section of Yancheng–Nantong HSR. However, limited research has been done to investigate the performance of screw-shaft pile reinforced subgrade. In this paper, numerical models were established to analyze the performance, especially the long-term settlement, of the reinforced subgrade. It was found that shaft-screw pile reinforced subgrade could control the long-term settlement better than the traditional shaft pile subgrade. The advantage becomes greater when the train speed increases. Moreover, the application of shaft-screw pile reinforced subgrade could reduce the material usage by about 10%. Briefly, shaft-screw reinforced subgrade could satisfy the settlement control requirements and achieve greater cost efficiency in sandy subgrades.