Suction caissons in dense sand, part I: installation, limiting capacity and drainage

Abstract

Suction caissons are a promising foundation concept for supporting offshore wind turbines. Compared to applications in the oil and gas industry, where most practical experience exists, significant differences arise in terms of load paths and magnitudes, soil type and caisson aspect ratio (skirt length to diameter). In a set of two companion papers, this contribution investigates the response of suction caissons in dense sand through a series of centrifuge experiments. The caisson was installed using suction, followed by sequences of cyclic loading and then extraction, all steps completed continuously in-flight. This first paper discusses installation, limiting capacities and drainage, whereas the second paper focuses on vertical cyclic loading into tension. The work demonstrates that suction caisson installation behaviour is well described by existing calculation methods. Tests performed at different installation rates demonstrate that careful assessment of the pumping rate is needed to ensure successful installation, with low pumping rates resulting in premature refusal. In the centrifuge tests, full skirt penetration was achieved without apparent loosening of the soil plug. The limiting capacity in tension, measured during the testing at both fast and slow uplift rates, was also well described by existing calculation methods.