Abstract: Modified suction caisson is a new type of suction foundation for offshore wind power engineering. Model tests were carried out to investigate the variation of cumulative rotation angle and its influencing factors of the regular suction caisson (RSC) and modified suction caisson (MSC) under horizontal cyclic loading. The cyclic loading mode includes one-way cyclic loading and variable-amplitude cyclic loading. The experimental results showed that the cumulative rotation angle of the RSC and MSC under horizontal cyclic loading mainly occurs within the first 200 loading cycles. The cumulative rotation angle was found to increase with the increase of cyclic loading amplitude and the number of loading cycles. However, the increasing rate of cumulative rotation angle decreases with the increase of loading cycle number. The relationship between the cumulative rotation angle and the number of loading cycles can be well fitted by a power function. By using Leblanc method and Miner’s rule, the cumulative rotation angle of the suction caisson foundation under long-term variable-amplitude cyclic loading was transformed into that under constant amplitude cyclic loading and then can be estimated. It was found that when the loading amplitude increases step by step, the predicted cumulative rotation angle of the RSC and MSC obtained by using the Leblanc method and Miner’s law is slightly higher than the measured model test results, indicating that the sequence and amplitude of cyclic loading have a certain influence on the cumulative rotation angle of the suction caisson foundation. In addition, the influence of cyclic loading on the ultimate bearing capacity of suction caisson foundation was studied and it was found that the ultimate bearing capacities of the RSC and MSC after cyclic loading are higher than those before cyclic loading. The research results can provide a basis for the design of the suction caisson foundation of offshore wind power.

Key words: modified suction caisson (MSC), cyclic loading, loading amplitude, cyclic loading sequence, cumulative rotation angle