Characterization of sand motions around vibrating vertical flat plates under saturated conditions

Monopile foundations of offshore wind turbines undergo continuous vibrations due to the cyclic lateral loads induced by waves and winds. To focus on the dynamics of sand behavior around vibrating foundations, researchers often conduct two-dimensional experiments using flat plates as representations of monopile foundations. This approach enables convenient observation of sand motions and bed deformation around the structure, facilitating a better understanding of how the sand responds to the cyclic vibrations. Previous studies have investigated sand motions around vibrating flat plates under dry conditions and found sand convective and subsidence motions around them. However, it remains unclear whether the same convective and subsidence motions occur under saturated conditions and if there are any differences in sand motions between dry and saturated conditions. Thus, this study with a simplified two-dimensional experiment is presented to further investigate the characteristics of sand motions under dry and saturated conditions. The experimental results indicate that the compacted sand surrounding the structure reduces the vibration amplitude of the monopile. But the vibration amplitudes are more significantly attenuated under saturated conditions compared to dry conditions. Moreover, the convective motions of sand under the saturated condition are weaker than those under the dry condition, which suggests that the viscous dissipation effect may weaken the convective motions around the vibrating monopile foundations.