To rapidly and precisely calculate the slender pile response and the soil resistance under lateral load in offshore wind power projects, the energy-based variational method was used to improve the calculation method of laterally loaded slender piles in layered elastic soil. Firstly, two cases were collected, the results were compared with that from the m-method, and numerical analysis or measured data were used to verify the accuracy of the improved method in this paper. Then, from the field test of a steel pipe pile in an offshore wind power project, the results from the improved method were compared with those from the numerical analysis and measured data, and the lateral soil resistance considering the layered shear effect and the distributed moment around the pile were discussed. The results show that the improved method in this paper can rapidly and precisely calculate the slender pile response under lateral load, and there is a 9~20% difference in the lateral soil resistance if the shear effect between each soil layer is considered. The ratio of the total distributed moment around the pile and the overturning moment at the pile head is less than 2%, and the resistance coefficient of m from this method provides the lower bound solution of the measured value.

The elastoplastic model can more accurately simulate the elastoplastic behavior of soil in the process of loading, so as to determine the soil resistance more accurately, which holds great significance in calculating the bearing capacity of pile foundations. However, the current study has not found that the elasticity of soil is taken into account to analyze the dynamic behavior of pile foundations. To study the dynamic response of pile foundation under horizontal cyclic load, theoretical calculation methods and model tests are applied. Based on the flexural differential equation of pile and considering the inertia force of the pile under harmonic load, the analytical solutions for the displacement and bending moment of pile foundation under horizontal cyclic load are obtained. The accuracy of the calculation method is confirmed through comparison with experimental results. An analysis is conducted to examine the impacts of harmonic load amplitude and frequency, foundation reaction coefficient, and pile bending stiffness on the plastic height. The changing rules of the pile bending moment and pile displacement with harmonic load amplitude, foundation reaction coefficient, and pile bending stiffness are studied. By comparing the theoretical and experimental results with numerical methods, it is found that the general trend of the experimental and theoretical results is consistent. It is found that as the harmonic load frequency increases, the foundation reaction coefficient decreases, and the harmonic load amplitude increases, there is a corresponding augmentation in the plastic height of the soil, pile displacement, and bending moment.

As one of the mooring foundation types for floating wind turbine platforms, research on the anchor pullout bearing characteristics of mooring pile foundations remains insufficient, and the underlying mechanism of anchor pullout bearing capacity needs further investigation and clarification. This paper conducts a numerical study on the bearing characteristics of mooring pile foundations under tensile anchoring forces with loading angles ranging from 0° to 90° and loading point depths of 0.2L, 0.4L, 0.6L, and 0.8L (where L is the pile length). The research findings indicate that the anchor pullout bearing capacity decreases as the loading angle increases from 0° to 90°, and exhibits a trend of first increasing and then decreasing with the increase in loading point depth. For rigid pile-anchors, the maximum anchor pullout bearing capacity occurs at a loading point depth of 0.6–0.8L, while for flexible piles, it appears at 0.4–0.6L. Both the bending moment and shear force of the pile shaft show abrupt changes at the loading point, where their maximum values also occur. This implies that the structural design at the loading point of the mooring pile foundation requires reinforcement. Meanwhile, the bending moment and shear force of the pile shaft gradually decrease with the increase in the loading angle, which is attributed to the gradual reduction of the horizontal load component. The axial force of the pile shaft also undergoes an abrupt change at the loading point, presenting characteristics where the upper section of the pile is under compression, the lower section is in tension, and both the pile top and pile tip are subjected to zero axial force. The depth of the loading point significantly influences the movement mode of the pile shaft. Shallow loading (0.2–0.4L) induces clockwise rotation, and the soil pressure around the pile is concentrated in the counterclockwise direction (90–270°). In the case of deep loading, counterclockwise rotation or pure translation of the pile shaft results in a more uniform stress distribution in the surrounding foundation soil, with the maximum soil pressure concentrated near the loading point.