Investigation of hybrid monopile foundations for offshore wind turbines under lateral cyclic loading in sand

Monopile foundation have been widely used for offshore wind projects. With growing size of offshore wind turbines and their deeper water depth, stronger foundations are needed. The hybrid monopile foundation, which combines a monopile with a friction wheel, is investigated in this study. A series of centrifuge tests was performed on foundation models under cyclic loadings in sandy soil. The tests were conducted on a monopile, a monopile with solid wheel, and a monopile with crashed stone wheel. The cyclic responses of the three models are described. Accumulated lateral displacements and lateral stiffnesses are investigated: the lateral displacement increases continuously with cycles but at a lower rate, and the stiffness tends to be larger during the cycles. The hybrid monopile foundation shows a better lateral capacity comparing to the original monopile foundation. The theoretical analyses of monopile foundations were introduced and compared with the experimental results. The results are aiming to optimize the design of offshore wind foundation and provide better in-service behaviors.