Granular segregation of layered sand beds around vertical piles under cyclic lateral vibrations

Recent studies on noncohesive sediment bed deformation and granular segregation induced by localized vibration from embedded vibratory piles indicate that vibrating vertical piles in uniform noncohesive sediment beds cause subsidence and convective sand motion. In practical engineering situations, offshore wind turbine piles, typically installed in stratified soil conditions, are subjected to continuous dynamic loading throughout their service life. However, the response of layered sand beds and the evolution of granular segregation around vibrating piles under these conditions are still not well understood. This study addresses this gap by investigating granular segregation characteristics in layered sand beds surrounding vibrating piles using a sandbox experimental system. It examines how the particle size ratio, vibration amplitude and frequency influence bed deformation and granular segregation. The findings reveal that both vibration amplitude and frequency significantly affect granular segregation and particle distribution within convective zones. Coarse particles emerge more rapidly and occupy larger horizontal areas of the bed surface at the equilibrium stage with increasing vibration intensity. The convective zone’s segregation rate exhibits an almost linear relationship with vibration intensity, with coarse particles occupying 19.15%–66.58% of the zone after prolonged vibration. Furthermore, the critical vibration intensity triggering granular segregation on the bed surface and within the convective zone under the experimental conditions is identified as 0.00896 and 0.0086, respectively, indicating a threshold for granular segregation in layered beds around vibrating piles. These insights advance the understanding of noncohesive sediment deformation and particle segregation around piles in vibration environments and may facilitate the understanding of the bed deformation of layered sand beds around the pile foundations of offshore wind turbines subjected to cyclic lateral vibration.