Numerical study on soil springs stiffnesses of laterally loaded monopiles

Abstract

Unlike traditional pile foundations, monopiles supporting offshore wind turbines usually have the characteristics of large diameter (D) and relatively low length-to-diameter ratio (L m /D). Accurate evaluation of the soil springs stiffnesses around the monopile is crucial for the design requirements and assessment of the dynamic response of offshore wind turbines. Over the past decade, a large number of initial stiffness models of lateral p-y spring have been proposed. However, limited research has been devoted to additional soil reaction springs, namely the rotational m-θ spring and pile base shear Q b-y b spring. Moreover, the contribution of these additional components is closely related to the pile-soil relative stiffness (K R), and it is a challenge to consider their relationship in the design. In this paper, a three-dimensional finite element analysis of elastic soil is performed to systematically investigate the effects of pile D, L m /D and soil elastic modulus (E s) on soil spring stiffness, and the effect of non-uniform soil is also discussed. The relationship between the initial load contribution ratio of each spring and the K R is clarified, and a new proposal for the soil springs stiffnesses considering the K R is put forward and verified for reasonableness.