Liquefaction-induced failure of pile foundations remains a critical challenge in seismic bridge engineering, particularly for large-diameter variable-section piles widely used in deep foundations. To address the limited understanding of their dynamic behavior in liquefiable soils, this study conducted large-scale shaking table tests on single and group pile foundations at the Xiang’an Bridge site in Xiamen. The model reproduced a stratified saturated sandy soil profile to examine pore pressure evolution, acceleration response, horizontal displacement, and bending moment under seismic intensities of 0.15 g, 0.25 g, 0.35 g, and 0.45 g. The experimental results validated the model’s reliability and revealed clear performance distinctions between the two pile types. As seismic intensity increased, the stable pore pressure ratio rose from 0.72 to 0.86, indicating progressive liquefaction. Compared with the single pile, the pile group exhibited 15–25% lower peak acceleration and displacement, and a delayed occurrence of maximum response by about 1.3 s. Damage occurred at 0.35 g for the single pile but only at 0.45 g for the pile group, accompanied by a more minor reduction in fundamental frequency (32.44% vs. 52.90%). These results demonstrate that the pile group effect mitigates the impact of liquefaction and enhances seismic resistance. The study provides experimental validation and quantitative insight into the dynamic response mechanisms of variable-section pile group foundations, contributing novel guidance for the seismic design of bridge foundations in liquefaction-prone regions.

A series of centrifuge model tests was performed to investigate the influence of subgrade surcharge loading on adjacent bridge pile foundations in soft soils, based on the Mingu Road project in Zhongshan City, China. Four surcharge distances (1D, 2D, 3D, and 4D, where D is the pile diameter) were examined to clarify the spatial–temporal evolution of pile–soil interaction. The results show that horizontal displacement, bending moment, and lateral soil resistance of the pile increase over time, exhibiting significant time-dependent behavior characterized by rapid initial growth followed by stabilization. As the surcharge distance increases, these responses decrease markedly, indicating a strong spatial attenuation effect. The bending moment along the pile depth follows a unimodal pattern with a peak at the soft soil layer. In contrast, the lateral soil resistance exhibits a similar trend of increase and decrease with depth. When the surcharge distance exceeds approximately 4D, the additional influence on the pile response becomes small. This study provides physical evidence and theoretical support for the safe design and construction of bridge pile foundations adjacent to road embankments in areas with soft soil.

To study the dynamic response characteristics of large-diameter step tapered group pile foundation under the condition of saturated sandy soil site under the action of different types of seismic waves, relying on the physical engineering of Xiang'an Bridge, through the shaking table test, the synthetic 5010 and 1004 waves, as well as Kobe and El Centro waves with the strength of 0.20g were selected to study the dynamic response characteristics of pile foundation group saturated sand around the pile, such as pore pressure ratio, pile shaft acceleration, pile top horizontal displacement, pile shaft bending moment, etc. The results indicate that, under earthquake conditions, saturated sand undergoes liquefaction, with a pore pressure ratio of about 0.6-0.8, which is linked to the spectral characteristics of the input seismic waves. The time-history response curve of pile end acceleration is more "dense" than that at the pile top and variable cross-section. Saturated sand has an amplification effect on acceleration, and the peak acceleration at the pile end, variable cross-section and pile top appears as a "lag" effect compared to the peak acceleration of seismic waves; The acceleration of the pile body reaches its maximum value under the action of 1004 waves; The relative displacement of the pile top produces the maximum value under the EL-Centro wave; Under the action of waves 5010, 1004, and Kobe, permanent lateral displacement occurs at the pile top; Under the action of 1004 waves, the peak bending moment of the pile body is the highest, and the moment when the peak bending moment occurs is the latest. Therefore, in the seismic design of group pile foundations on a saturated sand bottom, different types of seismic waves can be selected for checking calculations based on the specific characteristics of the pile foundations.