Lateral behavior of high-speed railway bridge pile foundation in soft soils under adjacent surcharge loads considering time-dependent characteristics

The adjacent surcharge caused by improper soil dumping and irregular backfilling poses a huge threat to the safe service of high-speed railway bridge pile foundations in soft soils. In this study, multiple-case field prototype tests including different surcharge distances and loading values and a numerical model embedded with a soft soil material subroutine were carried out to investigate the time-dependent lateral behavior of bridge piles. The time-dependent mechanism of pile-soil interaction was revealed by characterizing the variations of the additional lateral load acting on the pile shaft, the soil-arching stress between piles, and the plastic deformation in the soil around piles. The results show that with increasing load duration, the bending moment and deflection of the pile increase gradually, and their distribution is closely related to the thickness and location of the soft soil layer. Furthermore, the horizontal soil-arching between piles underwent the stages of stabilization, local damage, and plastic flow, in which the passive load acting on the pile side continued to increase until it stabilized, resulting in time-dependent lateral deflection of the pile foundation. Consolidation parameters and pile-soil stiffness ratios also have a significant effect on the time-dependent behavior of pile responses. The conclusions obtained can provide a valuable reference for engineering applications to predict the long-term behavior of bridge piles.