Comparison of the bearing capacities of composite foundations for offshore wind turbines
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摘要: 受到上部结构自重以及海洋环境荷载的影响，海上风电基础设计时应考虑竖向荷载、水平荷载以及弯矩荷载作用下基础的承载性能。本文通过有限元软件ABAQUS，对比研究了饱和黏土场地中大直径单桩基础、桩‒平台复合基础以及桩−筒复合基础在竖向荷载V、水平荷载H、弯矩荷载M作用下的承载性能。研究结果表明两种复合基础较单桩基础呈现出显著的承载性能优势。桩‒平台复合基础的竖向承载力、水平承载力以及抗弯承载力随着附加平台直径的增大呈指数型增加；桩−筒复合基础的竖向承载力以及抗弯承载力随着筒结构入土深度的增加先增大然后趋于稳定，桩−筒复合基础的水平承载力与筒直径以及筒入土深度为双参数线性增加关系。V‒H以及V‒M复合荷载加载条件下，两种复合基础比单桩基础的破坏包络线空间大，两种复合基础的稳定性相对单桩基础有显著提升。在一定承载范围内，附加平台结构或筒型结构可以减小桩的直径或入土深度。Abstract: With the aggravation of energy shortage and environmental pollution, the development and utilization of renewable energy have become the focus of research in countries around the world. As a green renewable energy source, offshore wind energy is one of the effective ways to solve these problems. The foundation form of built offshore wind farms is mainly large-diameter monopile. With the development of offshore wind farms expanding toward the deep sea, the applicability of the large-diameter monopile is confronted with some significant challenges. The exploration and research of a new type of foundation are important and meaningful. Affected by the weight of the superstructure and the load of the marine environment, the design of offshore wind turbine foundations should consider the bearing performance of the foundation under vertical load, horizontal load, and bending moment. The ABAQUS software was used to compare the bearing capacities of large-diameter monopile, pile–plate composite foundation, and pile–bucket foundation in saturated clay under vertical load V, horizontal load H, and bending moment M. Results show that the bearing capacities of the two composite foundations are better than the bearing capacities of the monopile foundation. The vertical, horizontal, and bending bearing capacities of pile–plate composite foundations increase exponentially with the increase in the diameter of the plate. The vertical and bending bearing capacities of the pile–bucket foundation increase with the increase in the buried depth of the bucket structure increasing, and the increasing trend gradually weakens parallel to the line. The horizontal bearing capacity of the pile–bucket foundation has a linear relationship with the diameter and buried depth of the bucket structure in the soil. Under the composited loading conditions of V–H and V–M, the failure envelope spaces of the two composite foundations are larger than those of the monopile, and the bearing performance of the two composite foundations is significantly better than that of the monopile.
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图 1 单桩、桩− 平台复合基础、桩− 筒复合基础示意图
Figure 1. Monopile, pile–plate composite foundation, and pile–bucket composite foundation
图 5 桩‒平台复合基础竖向承载特性。（a）v‒V图；（b）竖向极限承载力与平台直径的关系；（c）桩‒平台复合基础竖向极限承载力提高系数
Figure 5. Vertical bearing characteristics of pile–plate composite foundations: (a) v–V; (b) relationship between vertical ultimate bearing capacity and diameter of the plate; (c) improvement coefficient of the vertical ultimate bearing capacity of the pile–plate composite foundation
图 6 桩‒筒复合基础竖向承载性能对比。（a）v‒V图；（b）桩‒筒复合基础竖向极限承载力与筒直径的关系；（c）桩‒筒复合基础竖向极限承载力提高系数
Figure 6. Vertical bearing characteristics of pile–bucket composite foundations: (a) v–V; (b) relationship between vertical ultimate bearing capacity and diameter of the bucket; (c) improvement coefficient of the vertical ultimate bearing capacity of the pile–bucket composite foundation
图 7 桩‒平台复合基础水平承载特性。（a）h‒H图；（b）水平极限承载力与平台直径的关系；（c）桩‒平台复合基础水平极限承载力提高系数
Figure 7. Horizontal bearing characteristics of pile–plate composite foundations: (a) h–H; (b) relationship between horizontal ultimate bearing capacity and diameter of the plate; (c) improvement coefficient of the horizontal ultimate bearing capacity of the pile–plate composite foundation
图 8 桩‒筒复合基础水平承载性能对比。（a）h‒H图；（b）桩‒筒复合基础水平极限承载力；（c）桩‒筒复合基础水平极限承载力提高系数
Figure 8. Horizontal bearing characteristics of pile–bucket composite foundations: (a) h–H; (b) relationship between horizontal ultimate bearing capacity and diameter of the plate; (c) improvement coefficient of the horizontal ultimate bearing capacity of the pile–plate composite foundation
图 9 桩‒平台复合基础抗弯承载性能对比。（a）θ‒M图；（b）桩‒平台复合基础抗弯极限承载力；（c）桩‒平台复合基抗弯极限承载力提高系数
Figure 9. Bending bearing characteristics of pile–plate composite foundations: (a) θ–M; (b) relationship between ultimate bending capacity and diameter of the plate; (c) improvement coefficient of the ultimate bending capacity of the pile–plate composite foundation
图 10 桩‒筒复合基础抗弯承载性能。（a）θ‒M图；（b）桩‒筒复合基础抗弯极限承载力；（c）桩‒筒复合基础抗弯极限承载力提高系数
Figure 10. Bending bearing characteristics of pile–bucket composite foundations: (a) θ–M; (b) relationship between ultimate bending capacity and diameter of the bucket; (c) improvement coefficient of the ultimate bending capacity of the pile–bucket composite foundation
图 11 V‒H加载条件下基础的破坏包络线。（a）桩‒平台复合基础；（b）筒直径为10 m时桩‒筒复合基础；（c）筒直径为15 m时桩‒筒复合基础；（d）筒直径为20 m时桩‒筒复合基础
Figure 11. V–H failure envelopes of (a) pile–plate composite foundations; (b) pile–bucket composite foundations (the diameter of the bucket is 10 m); (c) pile–bucket composite foundations (the diameter of the bucket is 15 m); (d) pile–bucket composite foundations (the diameter of the bucket is 20 m)
图 12 V‒M加载条件下基础的破坏包络线。（a）桩‒平台复合基础；（b）筒直径为10 m时桩‒筒复合基础；（c）筒直径为15 m时桩‒筒复合基础；（d）筒直径为20 m时桩‒筒复合基础
Figure 12. V–M failure envelopes: (a) pile–plate composite foundation; (b) pile–bucket composite foundation (the diameter of the bucket is 10 m); (c) pile–bucket composite foundation (the diameter of the bucket is 15 m); (d) pile–bucket composite foundation (the diameter of the bucket is 20 m)
图 13 破坏包络线参数敏感性分析。（a）V‒H；（b）V‒M
Figure 13. Parameter sensitivity analysis of failure envelopes: (a) V–H; (b) V–M
表 1 荷载及位移符号规定
Table 1. Sign conventions for loads and displacements
Description of physical symbols Vertical loading Horizontal loading Bending moment Loading V H M Ultimate bearing capacity Vult Hult Mult Dimensionless loading V/(ASu) H/(ASu) M/(ADSu) Dimensionless ultimate bearing capacity Vult/(ASu) Hult/(ASu) Mult/(ADSu) Displacement v h θ 
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