Response of suction caissons for tidal current turbine applications in soft clay to monotonic and cyclic vertical loading

In soft marine clays, suction caissons provide a foundation system for tidal current turbines that further promote the sustainable nature of the system by allowing for their removal at the end of the structure’s design life. When configured as a multipod, the moment loads resulting from the horizontal flow of water will be transferred to the suction caissons as compression–uplift loads on opposing foundation legs. The behavior of a suction caisson in soft clay was investigated at aspect ratios of 1 and 2 under monotonic and cyclic vertical loading applicable to multipod-supported tidal current turbine design. Installation and solely monotonic vertical load tests indicated lower back-calculated adhesion factor, α, values and higher back-calculated bearing capacity factor, Nc, values than design standards recommend. The capacity and stiffness response of the foundation after undergoing cyclic loading was found to be largely dependent on the magnitude of displacement the foundation underwent during cyclic loading. Additionally, a threshold of elastic foundation response was observed during cyclic loading defined by a cyclic displacement amplitude. These results indicate serviceability constraints will be critical in the design of suction caisson foundations for tidal current turbine applications.