Lateral behavior of monopiles in sand under monotonic loading: Insights and a new simple design model

This paper presents a synthesis of recent and new research conducted by the authors on laterally loaded monopiles in drained sand. The research involved reduced-scale field tests, centrifuge model tests, finite element (FE) simulations and comparisons of design approaches with published experimental data. The influence of the monopile base on lateral response is first discussed by drawing on field tests and numerical simulations and it is shown that the base generally provides a negligible contribution. The applicability of the API p-y formulation is then investigated through systematic FE analyses. The results show that this formulation leads to inaccurate predictions largely due to the assumption of a high initial stiffness varying linearly with depth and an unrealistic hyperbolic tangent back-bone function. Based on new insights into pile-soil interaction together with elastic simulations of laterally loaded rigid piles and new observations based on 26 pile tests, a simple rotational spring model is proposed to allow rapid quantification of the non-linear response of rigid monopiles in uniform sand. The effect of monopile flexibility is then added through a new straightforward correction factor based on 80 extra FE simulations. Finally, an example application of the proposed approach for a typical monopile design is presented.