Abstract: Long-pile groups of railway foundation undergo excessive settlements after groundwater reductions, which may exceed the settlement limit and threaten the safe operation of high-speed trains. However, the effect of groundwater reduction on a long-pile group (greater than 20 m in length) has not been fully understood, especially in respect of repeated reductions. In this study, a centrifuge test was conducted to investigate the responses of pile groups in silty soils subjected to repeated falls in the water table. The behavior of the piles was discussed based both on the test and on 3D numerical analyses. With the derived coefficient β for the axial force evaluation of the pile, the effect of lowering the water table on the railway pile foundation could be seen. Results of the tests and numerical analyses indicated that the water table decline significantly increased the down-drag and axial force of the pile, causing significant settlement. A longer pile presented a larger axial force at the neutral point. Nevertheless, the incremental percentage of the axial force decreased with increasing pile length with the same water table reduction. Because of group effect, the displacement of soil next to the center pile was smaller than that near the corner piles and showed a similar trend as the axial force of the pile. As the water table fell, the static load ratio affecting the progress of pile settlement increased disadvantageously, possibly inducing excessive pile settlement. A design method for railway pile foundations taking account of lowering groundwater was proposed with an example application, which provided a reference for similar projects.

Key words: High-speed railway; Pile foundation settlement; Centrifuge testing; Numerical modelling; Groundwater declining; Drag load

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