Centrifuge study on the cyclic performance of caissons in sand

Suction caissons are currently considered as an alternative to monopile foundations for met masts and offshore wind turbines. This paper presents the results of a series of centrifuge tests conducted on cyclically loaded suction caissons in very dense dry sand. Two representative caisson foundations were modelled at a 1200 scale in a geotechnical centrifuge and were subjected to a number of different cyclic loading regimes, for up to 12 000 cycles, both of which add to previous data sets available in the literature. During each test, changes in stiffness, the accumulation of rotation and settlement of the system were measured. It was found that the rotational caisson stiffness increased logarithmically with the number of loading cycles, but to a much lower extent than previously reported for monopiles. Similarly the accumulation of rotation was also observed to increase with number of cycles and was well described using a power relationship. An aggregation of rotation was also observed during two-way tests and is believed to be caused by the initial loading cycles that create a differential stiffness within the local soil. Predictions were then made as to the behaviour of a prototype structure based upon the observed test results and established influence parameters.