Field trials of suction caissons in clay for offshore wind turbine foundations

A programme of testing of caisson foundations in clay at the Bothkennar test site is described. The tests are relevant to the design of foundations for offshore wind turbines, in the form of either monopod or tetrapod foundations. Records are presented for installation of the caissons, cyclic moment loading under both dynamic and quasi-static conditions, cyclic inclined vertical loading, and pullout of the caisson. Variation of stiffness of the foundation is observed, with high initial stiffness followed by hysteretic behaviour at moderate loads and degradation of response at high loads. Some implications for the design of wind turbine foundations are briefly discussed.