Abstract: Based on one-dimensional consolidation-creep tests, comprehensively considering primary consolidation and creep effects, the one-dimensional Koppejan model was selected to characterize the time-dependent deformation of soft soils, and the model was extended to the three-dimensional stress space in incremental form, and the corresponding material subroutine was implemented in ABAQUS software. The subroutine was then applied to a numerical analysis considering pile-soil coupled interactions based on a field prototype test. The time-dependent variations of pile response, additional pressure acting on the pile shaft, and the soil-arching between piles under long-term surcharge loads were investigated, and the mechanism of time-dependent interaction between passive piles and soft soils was revealed. Results show that the additional load caused by the surcharge load is mainly distributed in the relatively soft-weak layer, and increases with increasing duration of loading, but its distribution range is unchanged. With increasing duration of loading, the soil plastic zone between the passive piles enlarges, the arch height of principal-stress decreases, and the soil-arching effect continues to weaken. The weakening law of the soil-arching effect changes with the change of surcharge conditions. The smaller the surcharge distance or the greater the surcharge load is, the longer the time for the pile response reach a steady growth stage, and the more significant the time-dependent influence of soft soil deformation on pile response is. For different thicknesses of soft soils, the distribution range of the additional load acting on the pile shaft is different, resulting in different influences of the surcharge load or the loading duration on the pile response distribution. The deduced extended Koppejan model well reflects the process of time-dependent interaction between the pile foundation and soft soils and provides reference for the prediction of the long-term lateral deformation of pile foundations.

Key words: adjacent surcharge load, pile-soil interaction, time-dependent deformation, extended Koppejan model, numerical analysis