Inner frictional resistance of super-large-diameter steel pipe piles in sand
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摘要: 近年来随着海上风电装机容量的不断增加,超大直径钢管桩基础的应用越来越广泛。桩径增加导致了在小直径钢管桩中出现的土塞闭塞效应减弱或完全消失,准确计算管桩的内侧摩阻力变得尤为重要。开展了砂土中超大直径钢管桩竖向承载特性的离心机模型试验,采用了双壁桩形式重点研究钢管桩内侧摩阻力的发挥规律,与数值模拟方法相结合系统研究了直径大于4 m,不同径长比钢管桩内侧摩阻力的发挥规律,将计算结果与现行的API规范方法进行了对比,并提出了内侧摩阻力的计算方法。研究揭示,超大直径钢管桩内侧摩阻力的发挥呈现桩端大并沿桩身迅速减小的三角形模式,当径长比小于0.2时,API规范方法计算得到的钢管桩内侧摩阻力偏大。Abstract: In recent years, with the increasing installed capacity of offshore wind power, the super-large-diameter steel pipe pile foundation has been widely applied. As the effect of soil plug weakens or disappears with the increase of the pile diameter, accurately calculating the inner frictional resistance of super-large-diameter steel pipe piles is especially important. In this study, the centrifugal model tests on the vertical bearing capacity of super-large-diameter steel pipe piles in sand are carried out using the double-wall pile form to study the inner frictional resistance. Then the action laws of the inner frictional resistance under different diameter-to-length ratios of steel pipe piles with diameter larger than 4 m are studied using the numerical simulation method. The calculated results are compared with API standard, and a new formula for calculating the inner frictional resistance is proposed. The research reveals that the inner frictional resistance of the super-large-diameter steel pipe pile shows a triangular pattern with the pile end greatly decreasing along the pile body. When the diameter-to-length ratio is less than 0.2, the inner frictional resistance of the steel pipe pile calculated by API standard is too large.
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表 1 模型桩和原型桩的参数
Table 1 Parameters of model and prototype piles
桩型 直径D/m 入土桩长L/m 径长比D/L 壁厚t/mm 抗压刚度/(103 MN) 原型桩P1 4.00 50.0 0.08 84 217.0 原型桩P2 8.00 50.0 0.16 94 490.0 模型桩M1 0.04 0.5 0.08 7 21.7 模型桩M2 0.08 0.5 0.16 7 48.8 表 2 试验安排
Table 2 Test programmes
试验组次 模型桩 每级加载/N V-1 M1 300 V-2 M2 750 表 3 计算组次安排
Table 3 Arrangement of finite element calculation
编号 桩长D/m 桩长L/m 径长比D/L 壁厚t/mm P4-50-90 4 50 0.08 90 P5-50-90 5 50 0.10 90 P6-50-90 6 50 0.12 90 P7-50-90 7 50 0.14 90 P8-50-90 8 50 0.16 90 P6-25-90 6 25 0.24 90 P6-30-90 6 30 0.20 90 P6-40-90 6 40 0.15 90 P6-35-90 6 35 0.24 90 P6-60-90 6 60 0.10 90 P6-70-90 6 70 0.09 90 P6-50-70 6 50 0.12 70 P6-50-80 6 50 0.12 80 P6-50-100 6 50 0.12 100 P6-50-110 6 50 0.12 110 表 4 有限元计算结果与API计算结果对比
Table 4 Comparison between finite element and API results
编号 径长比D/L 有限元计算 API计算 承载力Qc/MN 内侧摩阻力Qfi,c/MN 外侧摩阻Qfe,c力/MN 端阻Qp/MN 承载力Qc/MN 内侧摩阻力Qfi,c/MN 外侧摩阻Qfe,c力/MN 端部阻力Qp/MN P4-50-90 0.08 78.11 15.81 53.08 9.22 81.61 37.17 38.92 5.53 P5-50-90 0.10 105.17 24.59 66.97 13.61 102.49 46.90 48.65 6.94 P6-50-90 0.12 137.09 36.43 81.11 19.55 123.36 56.63 58.38 8.36 P7-50-90 0.14 171.73 50.15 95.44 26.14 144.23 66.36 68.11 9.77 P8-50-90 0.16 207.64 64.89 110.68 32.06 165.10 76.08 77.84 11.18 P6-25-90 0.24 72.50 31.34 20.68 20.48 47.58 19.60 20.21 7.77 P6-30-90 0.20 81.26 31.00 29.72 20.54 63.20 27.01 27.84 8.36 P6-35-90 0.17 94.00 32.56 40.13 21.31 78.24 34.41 35.48 8.36 P6-40-90 0.15 107.12 33.80 52.06 21.26 93.28 41.82 43.11 8.36 P6-60-90 0.10 172.82 38.94 116.53 17.34 153.44 71.44 73.65 8.36 P6-70-90 0.09 211.24 37.58 157.90 15.76 183.52 86.25 88.91 8.36 -
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