Field test on the mechanism of composite bucket foundation penetrating sandy silt overlying clay

Abstract

Composite bucket foundation has been gradually applied in China, involving six tilting supports to connect an upper pillar with a lower suction bucket with even honeycomb components separated by bulkheads. However, there are limited field measurements for such new type of offshore wind turbine foundation structure currently. In this study, field test campaign is launched to investigate the evolution of critical parameters for composite bucket foundation during the penetration process in soils. Results indicate that the coefficient of lateral pressure on the exterior skirt increases dramatically when traversing a shallow sandy silt layer, and the maximum value is approximately 2.81 times the passive soil pressure coefficient; the presence of negative pressure within the bucket causes a coefficient of lateral pressure on the interior skirt within the range between active and passive pressure coefficients. Nonetheless, as the penetration depth increases, the muddy-silty clay layer inside the bucket prevents further generation of seepage channels. By comparing the volume of seawater discharged from the bucket with its penetration volume into the mud surface, it is found that the bucket is under an over-speed penetration state. This study serves to promote the understanding of self-weight and negative pressure penetration mechanism for composite bucket foundation.