Generalized Solutions for Lateral Bearing Behavior of Large Diameter Monopile Foundation for Offshore Wind Turbine Considering Double Additional Moment Effects

Abstract

To examine the influence of double additional moment effects on lateral response of large diameter monopile foundation, this work firstly establishes analytical constitutive relation of additional moment versus pile slope (Ms-θ) induced by vertical shaft resistance and constitutive model of additional moment to slope (Mg-θ) subjected to the gravity of soil core inside steel pipe pile, respectively. Furthermore, the analytical model and differential expressions of pile element are developed with consideration of the presented double additional moment effects. By means of transfer matrix method and Laplace transformation, this work deduces the analytical solutions of transfer matrix coefficients for pile in elastic and plastic state and obtains the responses of larger diameter monopile foundation. The proposed methodology is validated via comparing its predictions with the literatures results. Success of proposed methodology is illustrated, which implies that the proposed method can be used to evaluate the pile response under actions of vertical shaft resistance and axial force along pile shaft effectively. Finally, parametric study of additional moments is performed and the results reveal that, for the influence of vertical shaft resistance, decreasing ratio of pile responses will increase with increasing limit skin friction τu, pile diameter d or decreasing equivalent critical displacement su,eq, in which d and su,eq have more notable influence. In other word, the influence of vertical shaft resistance cannot be ignored for monopile foundation with large diameter and for stiff soil mass around pile. Although factors, including stiffness, gravity, length of soil core, diameter and embedded length of pile, as well as the stiffness of soil mass around pile, have impact on the lateral bearing capacity of pipe pile when considering soil core effect, the influence of additional moment Mg due to soil core is too small (within 0.1%) to be neglected.