Wave-Induced Liquefaction and Stability of Suction Bucket Foundation in Drum Centrifuge

Abstract

This paper discusses the instability of suction bucket foundations that are growing in importance for bottom-mounted offshore wind turbines in association with wave-induced liquefaction of sand beds. The instability of suction bucket foundations should be understood in light of fluid–soil–structure interactions. In this study, we investigated the instability using centrifuge wave testing in a drum channel with viscous scaling to match the time-scaling laws for fluid wave propagation and consolidation of the soil. This paper highlights the effects of loosening and heaving of the sand inside the bucket during the installation process, which is one of the onsite problems, on the overall stability and clarifies the stability of the whole system in light of wave–soil–structure interactions. The experimental results showed that the instability of the suction bucket is ascribed to the occurrence and progress of liquefaction of the sand bed around the bucket. The experimental results further demonstrated the effect of embedment of the bucket in a dense layer. An embedded depth of the bucket tip equal to one-third of the bucket skirt length prevented instability of the foundation, despite the spread of liquefaction in the loose sand bed. Even when the dense sand inside and underneath the bucket was loosened during the installation process, the foundation bucket remained stable against severe wave actions. The present study examined and summarized the overall stability of suction bucket foundations in sand beds under severe wave loading and clarified the importance of the progress of liquefaction around the foundations.