Influence of Low-Permeability Layers on the Installation and the Response to Vertical Cyclic Loading of Suction Caissons

Abstract

Offshore wind is a key part of the change toward renewable energy sources. Offshore wind farm developments are moving to sites that are characterized by increased water depths and layered soil profiles, e.g., in the North Sea. Suction caisson–based jacked structures are expected to be increasingly used to support wind turbines at such sites. Experience of suction caissons serving as foundations for offshore wind turbines is limited. The mechanisms governing the suction caisson installation in layered soils are poorly understood and no published data of the in-service performance of suction caisson jackets supporting offshore wind turbines in layered soils exists. This gap is addressed here through a series of centrifuge tests investigating the installation and the response of suction caissons in layered soils—sand over clay and clay over sand—subjected to vertical cyclic loading into tension. The results reveal the mechanisms enabling suction caisson installation in layered soils and the complex load transfer mechanisms governing the suction caisson response under vertical cyclic loading. The clay layer plays a key role: in sand over clay, it encapsulates the sand plug, which leads to predominantly undrained behavior. In clay over sand, the uplift of the clay soil plug is critical both in facilitating suction installation and in response to vertical cyclic loading in tension. These findings provide confidence for suction installation and caisson response under vertical cyclic loading into tension in layered soils.