Numerical analysis of post-cyclic ultimate bearing capacity of helical anchors in clay

Helical anchors, serving as foundations for floating offshore structures on clay seabeds, experience cyclic loading that significantly impacts their ultimate bearing capacity. However, accurately assessing this post-cyclic loading capacity remains challenging. To address this, a 3D finite element model incorporating the E-R model is developed to investigate the effects of cyclic loading patterns and soil parameters of clay on the ultimate bearing capacity. The underlying mechanisms driving capacity changes are explored through the lens of soil strength evolution and failure mechanisms. Results indicate that increases in cyclic amplitude markedly reduce the horizontal bearing capacity by up to 43% at 0.5q_ref. Additionally, greater horizontal loading angles and higher soil sensitivity diminish capacity, whereas the capacity reduction by only 4% as the loading period increases from 2s to 6s. This reduction is associated with localized soil strength degradation near the shaft and helix edge, as well as changes in failure mechanisms under cyclic loading, both of which contribute to the observed decrease in bearing capacity. Consequently, a predictive expression for estimating post-cyclic ultimate bearing capacity is developed through a polynomial nonlinear least square fitting, providing a practical tool for design optimization and enhanced industrial guidance.