Effects of drainage conditions and suction pressure on tensile response of bucket foundations: An experimental study

Suction buckets acting as supports for jacket structures may constitute a viable foundation solution for offshore wind turbines. While monopiles dominate the industry, suction buckets remain uncommon despite their advantages in transitional water depths. One of the reasons stems from challenges of achieving optimal design due to scarce experience and knowledge, as the mechanisms governing foundation response to different drainage conditions are poorly understood. This paper contributes with new insights into tensile behavior of suction buckets based on experimental evidence. A defining property of bucket foundations is the ability to withstand extreme uplift forces on account of suction, which represents the core subject of this study. All tests involved a medium-scale model installed in sand in a pressurized environment. A novel feature of this research consists of examining the relative importance of soil density. By varying the relative density (40–90%) and the uplift rate (0.05–500 mm/s), a full range of drainage and soil conditions was explored. Suction pressure generated during partially drained or fully undrained uplift tends to reach similar values regardless of initial relative density. This key finding demonstrates how the soil state is altered due to jacking installation and cyclic pre-shearing. Regression models are established to capture the dependency of tensile capacity and initial stiffness on uplift rate.