Dynamic response characteristics of an offshore, wind-power monopile foundation in heterogeneous soil
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摘要: 采用有限元分析軟件ABAQUS建立了非均質土中海上風電單樁基礎數值計算模型，將樁基礎受到的波浪、洋流及風荷載等效成雙向對稱循環荷載，對水平循環荷載作用下樁身水平位移、樁身剪力、樁身彎矩和樁側土抗力進行了研究，并對不同循環次數下樁身水平位移進行了對比分析。研究表明，樁身水平位移隨時間變化逐漸累積，隨著循環次數的增加，泥面處樁身最大位移發生的時間點滯后；樁身剪力出現負值；樁身彎矩最大值發生在淺層土體；樁身外壁土抗力曲線隨時間的變化在埋深約2/3處出現分界點，分界點上下范圍內土抗力變化規律正好相反，在淤泥土和粉砂土分界面處增加顯著；不同時間點樁身內壁沿埋深承擔的荷載基本不變。Abstract: Wind energy is a new kind of inexhaustible energy. It is gradually replacing the traditional energy as its pollution-free and renewable. China has a long coastline, abundant offshore resources, and vast offshore space. Offshore wind farms have gradually become the focus of wind-power development. Large-diameter single-pile foundations are being widely used in the field of offshore power generation because of advantages including convenient manufacture and installation, clearer stress conditions compared with pile groups, and affordable cost and economy. Therefore, it becomes significantly relevant to study the dynamic response characteristics of large-diameter single-pile foundations under horizontal cyclic loads to eliminate the dangers hidden in engineering and installation and ensure normal usage during service. A numerical calculation model of an offshore, wind-power monopile foundation in heterogeneous soil was established by the finite element analysis software ABAQUS. The wave, ocean current, and wind load on the monopile foundation were equivalent to a bidirectional symmetrical cyclic load. The horizontal displacement, shear force, and bending moment along the pile shaft, and pile-side soil resistance under the horizontal cyclic load were studied. Furthermore, the horizontal displacements along the pile shaft under different cyclic times were compared with one another and analyzed. The results show that the horizontal displacement along the pile shaft accumulates gradually with time, and with increase in the number of cycles, the time lag of the maximum displacement of the pile body at mud surface occurs. The shear force along the pile shaft appears negative. The maximum bending moment of the pile body occurs in shallow soil. The variation in the soil-resistance curve of the pile body vs time occurs at a cut-off point at approximately 2/3 of the buried depth. Additionally, the variation laws of soil resistance within the upper and lower boundaries of the cut-off point are just the opposite of each other. The soil resistance increases significantly at the interface between silt and silty soil. The load along the buried depth of the inner wall of the pile remains unchanged at different time points.
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圖 1 非均質土中海上風電單樁基礎數值計算模型
Figure 1. Numerical model of offshore wind power monopile foundation in heterogeneous soil
圖 4 第20次循環時樁身水平位移變化曲線。（a）前5 s；（b）后5 s
Figure 4. Horizontal displacement variation curves along the pile shaft during the 20th cycle: (a) first 5 s; (b) next 5 s
圖 5 第20次循環時樁身剪力變化曲線。（a）前5 s；（b）后5 s
Figure 5. Shear force variation curves along the pile shaft during the 20th cycle: (a) first 5 s; (b) next 5 s
圖 6 第20次循環時樁身彎矩變化曲線。（a）前5 s；（b）后5 s
Figure 6. Bending moment variation curves along the pile shaft during the 20th cycle: (a) first 5 s; (b) next 5 s
圖 7 第20次循環時樁身外壁土抗力埋深分布曲線。（a）前5 s順載側；（b）后5 s逆載側
Figure 7. Soil resistance distribution curves of pile outer wall along the buried depth during the 20th cycle: (a) forward side of the first 5 s; (b) reverse load side after 5 s
圖 8 第20次循環時樁身內壁土抗力埋深分布曲線。（a）前5 s順載側；（b）后5 s逆載側
Figure 8. Soil resistance distribution curves of pile inner wall along the buried depth during the 20th cycle: (a) forward side of the first 5 s; (b) reverse load side after 5 s
圖 9 第N次循環時泥面處樁身和樁底端水平位移。（a）泥面處；（b）樁底端
Figure 9. Horizontal displacement of pile shaft at mud surface and pile bottom at the Nth cycle: (a) at the mud level; (b) bottom end of pile
圖 10 第N次循環結束時泥面處樁身和樁底端水平位移。（a）泥面處；（b）樁底端
Figure 10. Horizontal displacement of pile body at the mud surface and pile bottom at the end of the Nth cycle: (a) at the mud level; (b) bottom end of pile
表 1 樁周土及樁端土參數
Table 1. Parameters of soil around pile and soil at pile end
Soil layer Thickness/
mElasticity modulus/
MPaPoisson’s
ratioEffective weight/
(kN·m?3)Cohesive force/
kPaInternal friction angle/
(°)Dilatancy angle/
(°)Mucky clay 28 6.6 0.3 7.5 17.6 12.8 0.1 Silt 16 6.4 0.3 6.2 19.8 11.6 0.1 Silty sand 56 39.5 0.3 9.1 4.5 31.3 15 
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表 2 樁的物理力學參數
Table 2. Physical and mechanical parameters of pile
Pile diameter/m Wall thickness/mm Burial depth/m Pile length/m Elasticity modulus/GPa Poisson’s ratio Effective weight/(kN·m?3) 5 70 50 66 210 0.3 68
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