Experimental study on current-induced local scour and pre-embedded protective measures of multi-bucket jacket foundation for offshore wind turbines

The multi-bucket jacket foundations (MBJF) have been extensively applied in offshore wind farms in China. Scour significantly affects the in-situ stability of wide and shallow MBJF, but existing scour protection methods fail to adequately account for the structural and construction characteristics of wide, shallow buckets and their suction installation. Thus, their applicability to MBJF in harsh marine environments is limited. This study has proposed a pre-embedded protection method (referring to the placement of the bucket lid below the seabed to enhance the stability and safety of the foundation under scouring conditions) and designed detailed experiments. A 3D structured light depth measurement technique was employed to capture terrain morphology, and high-resolution elevation images were generated using point cloud reconstruction for scour analysis and statistics. This study has revealed the influence patterns of the lid elevation, inflow angle, flow intensity, and water depth on the current-induced scour characteristics and protection efficiency of MBJF with pre-embedded protection. Based on model test results, predictive formulas for maximum scour depth and scour extent under pre-embedded protection were derived and refined. The results indicate that pre-embedded protection measures are highly efficient under various lid elevations, inflow angles, flow intensities, and water depths. Notably, flow intensity is the most sensitive factor influencing scour characteristics. An increase in embedded depth reduces both maximum scour depth and scour extent, with protection efficiency reaching up to 52% and 70.1%, respectively, in certain cases. An extreme angle that generates the greatest scour depth is identified, which is 30° under the current experimental conditions. Moreover, an increase in flow intensity and a decrease in water depth both lead to an increase in scour depth, especially under live-bed scour conditions. These findings are of great significance for enhancing the stability and long-term operational safety of offshore wind turbine foundations, providing methodological and theoretical support for scour protection of similar foundations.