The use of backfilling to remediate sand motion issues around vibrating monopile foundations

Backfilling, as a common remedial countermeasure, is widely used in ocean engineering to address the scour or subsidence problem around offshore-structure foundations. However, the performance of the backfilling in solving subsidence problems around vibrating monopiles has not been studied, and the mixing mechanisms of the backfilling sand with the bed sand around the vibrating monopile remains unknown. To investigate these issues, an experimental study on characteristics of sand motions around vibrating monopile foundations after backfilling process is conducted. The experiments were designed in two-dimensional conditions and different particle sizes of backfilling sand were used. The time-dependent characteristic geometrical dimensions of the sand bed deformation around the vibrating monopile were measured, and the mean convective velocity around the vibrating monopile was measured by Particle Imaging Velocimetry (PIV) technology. The experimental results indicate that backfilling sand with a larger particle size can effectively reduce the depth of the subsidence hole and mitigate the sand convective velocity around the vibrating monopile, compared with backfilling material of smaller or the same size as the original sand bed. The findings of this study could help to develop effective remedial countermeasures to deal with the soil subsidence problems around the monopile foundations of offshore wind turbines.