Nonlinear lateral response of offshore large-diameter monopile in sand

Abstract

This paper presents a nonlinear analysis method for laterally loaded large-diameter monopiles. The method accounts for the effects of pile diameter and soil deformation on the modulus of horizontal subgrade reaction by considering a modified modulus of horizontal subgrade reaction. The solution considers the force and moment equilibrium of soil-pile system to calculate the response of the monopile to lateral loads. The influence of the soil side friction reaction on the ultimate horizontal resistance is evaluated considering the degradation of modulus of horizontal subgrade reaction due to large pile displacement. The predictions of the developed method compared favorably with the results obtained from full-scale field tests, centrifuge model tests and laboratory model tests as well as existing analytical methods. The developed analytical method is then applied to study the rigid rotation behaviour of offshore monopiles. The results demonstrated that under lateral loading at the pile head, the depth for rigid rotation point lies within 0.62L–0.73L (L is pile length), and the depth of the rotation point increases as the pile diameter increases. It was also found that the load eccentricity has a significant effect on the depth of the rotation point.