Bearing characteristics of pile–bucket composite foundations for offshore wind turbines
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摘要: 基于有限元軟件ABAQUS平臺，建立了非勻質飽和黏土場地的海上風電樁–筒復合基礎數值計算模型，對比研究豎向荷載V、水平荷載H和彎矩荷載M作用下不同筒結構尺寸的樁–筒復合基礎的承載力系數，并采用正交試驗法開展樁–筒復合基礎的各向承載性能的影響因素研究。結果表明，飽和黏土的非勻質特性系數K對豎向承載力系數NcV影響較小；K對水平承載力系數NcH和抗彎承載力系數NcM的影響呈指數型遞減。筒結構直徑D和入土深度L對各向承載力系數的影響存在交互作用。D對樁–筒復合基礎承載力系數的影響最大，可以通過增加筒結構直徑從而有效地提高樁–筒復合基礎的承載性能。研究結果為海上風電樁–筒復合基礎的設計提供了依據。Abstract: Offshore wind power has been the fastest-growing form of renewable energy for the last few years, owing to its effectiveness in achieving carbon neutrality through a reasonable and efficient utilization of wind power resources. With offshore wind farms gradually developing into the deep and far sea, greater attention is paid to the bearing characteristics of foundations for offshore wind turbines. Therefore, it becomes significantly important to explore new foundations, effectively promoting the development of offshore wind power. Numerous researchers have substantially investigated novel foundations for offshore wind turbines to help with offshore wind farm construction. Compared to other foundations, the pile–bucket composite foundation has obvious advantages in terms of bearing performance. In this paper, a series of numerical calculation models for pile–bucket composite foundations in heterogeneous saturated clay are established using the finite element software ABAQUS. Additionally, the undrained shear strength changes with depth are examined via field variables to explain soil heterogeneity in the finite element model. Next, the displacement control method is adopted to apply the vertical loading V, horizontal loading H, and bending moment M at the top of the foundation. Simultaneously, the ultimate bearing capacity of the foundations is obtained by the double tangent method, and the bearing capacity factors of each load direction are obtained by normalizing the ultimate bearing capacity in different calculations. To obtain the preliminary design method for the size of pile–bucket composite foundation, the priority of influencing factors is studied through the orthogonal test. The results show that the saturated clay coefficient K has a nominal effect on the vertical bearing capacity coefficient NcV. When K is different, NcV remains almost unchanged for a certain foundation. Concerning the impact of bucket shapes on the bearing capacity coefficient in three directions, great interaction is observed between the diameter D and the buried depth L of the bucket structure. The diameter of the bucket has the greatest influence on the bearing characteristics of the pile–bucket composite foundations, wherein increasing the former can significantly improve the latter. The research results provide a reference for the design of the pile–bucket composite foundation of an offshore wind turbine.
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圖 2 樁–筒復合基礎形狀、荷載加載條件及土體條件
Figure 2. Pile–bucket composite foundation geometry, load conventions, and saturated clay conditions
圖 5 樁–筒復合基礎水平承載系數NcH與K之間的關系. (a) D = 10 m; (b) D = 15 m; (c) D = 20 m
Figure 5. Horizontal bearing capacity factors of the pile–bucket composite foundations (NcH) with K: (a) D=10 m; (b) D=15 m; (c) D=20 m
圖 6 樁–筒復合基礎水平承載系數NcH與D(a)和L(b)的關系
Figure 6. Horizontal bearing capacity factors of the pile–bucket composite foundations (NcH) with D(a) and L(b)
圖 7 D和L對水平承載特性的影響
Figure 7. Effect of D and L on the horizontal bearing capacity factors
圖 8 樁–筒復合基礎豎向承載系數NcV與K之間的關系. (a) D = 10 m; (b) D = 15 m; (c) D = 20 m
Figure 8. Vertical bearing capacity factors of the pile–bucket composite foundations (NcV) with K: (a) D = 10 m; (b) D = 15 m; (c) D = 20 m
圖 9 豎向加載極限狀態基礎等效塑性應變云圖(a)和位移矢量圖(b)（D20L10K2-V）
Figure 9. Equivalent plastic strain distribution (a) and displacement vector diagram (b) under the ultimate vertical bearing state
圖 10 樁–筒復合基礎豎向承載系數NcV與D (a)和L (b)的關系
Figure 10. Vertical bearing capacity factors of the pile–bucket composite foundations (NcV) with D (a) and L (b)
圖 11 D和L對豎向承載特性的影響
Figure 11. Effect of D and L on vertical bearing capacity factors of pile–bucket composite foundations
圖 12 樁–筒復合基礎抗彎承載系數NcM與K之間的關系. (a) D = 10 m; (b) D = 15 m; (c) D = 20 m
Figure 12. Moment bearing capacity factors of the pile–bucket composite foundations with K: (a) D = 10 m; (b) D = 15 m; (c) D = 20 m
圖 14 樁–筒復合基礎抗彎承載力系數NcM與D (a)和L (b)的關系
Figure 14. Moment bearing capacity factors of the pile–bucket composite foundations with D (a) and L (b)
圖 15 D和L對抗彎承載特性的影響
Figure 15. Effect of D and L on the moment bearing capacity factors of the pile–bucket composite foundations
表 1 飽和黏土非勻質特性
Table 1. Inhomogeneous characteristics of saturated clay
K = kD/Sum Sum / kPa k / (kPa·m–1) 2 6.25 1.25 4 3.25 1.3 6 2 1.2 10 1.25 1.25 30 0.4 1.2 
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表 2 荷載及位移符號規定
Table 2. Sign conventions for loads and displacements
Parameter Vertical
loadingHorizontal
loadingBending
momentLoading V H M Ultimate bearing capacity Vult Hult Mult Bearing capacity
factorNcV = Vult/ASu0 NcH = Hult/ASu0 NcM = Mult/ADSu0 Displacement v h θ
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表 3 因素水平表
Table 3. Factors and levels
Levels d / m l / m D / m L / m K 1 5 25 10 2 2 2 6 30 15 6 4 3 7 35 20 10 6 4 8 40 25 14 8
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表 4 正交試驗方案及結果
Table 4. Orthogonal scheme and results
Case d / m l / m D / m L / m K NcH NcV NcM 1 5 25 10 2 2 6.94 11.27 1.13 2 5 30 15 6 4 3.67 7.21 0.48 3 5 35 20 10 6 3.50 7.31 0.37 4 5 40 25 14 8 3.44 8.24 0.33 5 6 25 15 10 8 5.10 10.75 0.72 6 6 30 10 14 6 10.02 16.46 1.65 7 6 35 25 2 4 1.89 4.16 0.17 8 6 40 20 6 2 3.76 7.17 0.36 9 7 25 20 14 4 4.35 10.80 0.54 10 7 30 25 10 2 3.65 8.44 0.34 11 7 35 10 6 8 10.26 18.29 1.83 12 7 40 15 2 6 5.35 9.83 0.66 13 8 25 25 6 6 2.80 7.09 0.28 14 8 30 20 2 8 3.09 6.85 0.34 15 8 35 15 14 2 7.69 12.86 0.86 16 8 40 10 10 4 12.18 21.36 2.14
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表 5 水平承載力系數NcH極差分析
Table 5. Range analysis of NcH
Coefficient d / m l / m D / m L / m K NcH(1) 17.68 19.26 39.57 17.49 22.13 NcH(2) 20.73 20.48 21.99 20.55 22.15 NcH(3) 23.79 23.41 14.71 24.48 21.84 NcH(4) 25.85 24.91 11.79 25.53 21.93 R of NcH 8.18 5.65 27.78 8.03 0.32 Priority of factors D>d>L>l>K
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表 6 豎向承載力系數NcV極差分析
Table 6. Range analysis of NcV
Coefficient d / m l / m D / m L / m K NcV(1) 34.66 40.32 67.70 32.11 40.41 NcV(2) 39.26 39.55 41.46 40.32 43.63 NcV(3) 47.40 43.33 32.54 48.51 41.54 NcV(4) 48.79 46.90 28.40 49.16 44.52 R of NcV 14.13 7.36 39.29 17.05 4.12 Priority of factors D>L>d>l>K
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表 7 抗彎承載力系數NcM極差分析
Table 7. Range analysis of NcM
Coefficient d / m l / m D / m L / m K NcM(1) 28.25 24.91 104.27 30.94 35.60 NcM(2) 36.86 35.04 36.70 42.98 49.91 NcM(3) 46.74 49.12 17.33 52.80 40.97 NcM(4) 57.82 60.59 11.38 42.96 43.19 R of NcM 29.57 35.67 92.89 21.86 14.31 Priority of factors D>l>d>L>K
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