Chapter 14: Suction caisson foundations for offshore wind turbines subjected to wave and earthquake loading: effect of soil–foundation interface

Construction of off-shore wind turbines of massive dimensions has recently become a major activity in the field of civil engineering as a result of European Union (EU) demands to produce 20% of its electricity by means of renewable energy sources by 2020. Uniquely, the foundation design of wind turbines is characterised by the challenging combination of relatively low weight and large horizontal loading due to the wind and wave currents, which produce large overturning moment at their bases (Houlsby & Byrne, 2000; Byrne & Houlsby, 2003).

Currently, several types of foundations are implemented for offshore wind turbines, depending on the site conditions and water depth. In waters of medium depth, the monopile option dominates the industry, with the alternative being a recently introduced scheme termed ‘suction caisson’, which was originally proposed for the foundation of off-shore oil platforms. It comprises a shallow footing whose capacity is enhanced by means of peripheral embedded skirts which confine the internal soil, thereby creating a soil plug. Ease of installation is the main advantage of this foundation type. The process consists of floating the caisson to its location, where it is driven into the seabed under the action of its self-weight and pumping of water trapped within the skirts. The differential pressure due to pumping creates suction which attracts the caisson lid downwards until it attains full contact with the soil.