Study on the Soil–Pile Interaction of Slender Piles in Multi-Layered Soil by the Variational Analysis Method

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.