Cyclic moment loading of suction caissons in sand

Suction caissons are being considered as a foundation option for offshore wind turbines. One configuration involves use of the caisson as a mono-foundation, in which case the moment-rotation response of the caisson must be well understood by the designers. The monotonic response has been the focus of recent research work and there is some guidance now available for engineers to use. However, less focus has been applied to the cyclic response and particularly to the long term response under cyclic loading. Over the lifetime of the turbine the foundation is likely to be exposed to many millions of cycles, of varying amplitude and period. One of the key issues that must be addressed by a designer is whether the accumulated rotation, over the life of the turbine, is acceptable. This paper presents experimental data from long term cyclic loading tests on caisson foundations. These tests can be used to develop a framework of response for long term cyclic loading. This paper describes the small scale cyclic loading rig used at Oxford and presents some typical results that give insight into the caisson response to a range of cyclic moment loading patterns. © 2011 Taylor and Francis Group, London