Comparison of monotonic and cyclic lateral response between monopod and tripod bucket foundations in medium dense sand

Abstract

The increasing trend of offshore wind turbines in deeper waters has necessitated the usage of alternative foundations such as the bucket foundation (including monopod and tripod). To investigate and compare the lateral monotonic and cyclic behaviour of the monopod and tripod, a series of centrifuge tests were carried out in medium dense sand, which were fabricated with an identical amount of material. The monotonic centrifuge tests were back-analysed using an advanced hypoplastic model to offer further insights into the test results. Under a monotonic lateral loading, the tripod exhibits a 78% higher initial lateral stiffness than the monopod, but it yields at a 71.4% smaller rotation, suggesting a more brittle response. While subjected to lateral cycling, the rotation of the monopod increases with number of cycles but at a decreasing rate, following a power function. Similarly, the dynamic stiffness of the monopod also increases with number of cycles. Differing from the monopod, the tripod exhibited a “self-healing” behaviour. Both the rotation and dynamic stiffness increases during the first few hundreds of cycling but decreases thereafter, leading to little variation. This unique feature in cumulative rotation and dynamic stiffness of the tripod makes it superior to the monopod.