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试验在长×宽×高=2 m×2 m×1 m的模型试验土槽中进行,自升式安装船试验模型由上部船体、桩腿以及桩靴3个部分组成。试验模型尺寸具体参数如表1所示。
表 1 自升式安装船试验模型尺寸
Table 1. Specific dimensions of the test model of the jack-up installation vessel
参数 尺寸/mm 参数 尺寸/mm 船体型长 945 桩靴高度 30 船体型宽 433 桩靴宽度 118 船体型深 76 桩靴长度 129 桩腿长度 867 桩靴中心圆孔直径 4 自升式安装船的模型实物如图1所示,为保证每次试验土样达到充分饱和状态,土箱内部设置进排水系统。如图2所示,水流从土体底部灌入渗流而上直到淹没整个土体并达到指定的水深,为减小对土体扰动,进水过程中尽量减小水流速度。图3为桩靴结构示意图,图3(a)为桩靴实物模型图,图3(b)为桩靴的尺寸示意图。
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本次试验采用福建标准砂,通过一系列室内土工试验得到基本砂土参数,如表2所示,颗粒级配曲线如图4所示。
表 2 砂土参数
Table 2. Parameters of the sandy soil
参数 数值 相对密实度 0.58 弹性模量/MPa 18 粘聚力/kPa 13.2 内摩擦角/(°) 32.5 最大干密度/[g·(cm)−3] 1.50 最小干密度/[g·(cm)−3] 1.28 比重/% 2.42 渗透系数/(cm·s−1) 0.039 筛分试验采用2 mm、1 mm、0.5 mm、0.25 mm、0.1 mm和0.075 mm的细筛对试验砂土开展了筛分试验。将各粒组含量百分比绘成如图4所示级配曲线,通过级配曲线判定该试验用土为砂土。由级配曲线可知,试验砂土D10=0.09 mm,D30=0.15 mm,D60=0.175 mm,通过公式(1)和公式(2)分别计算得到砂土的不均匀系数为1.94,曲率系数为1.43,由此判定试验砂土为级配连续性较好的均质砂土。
$$ {C_{\rm{u}}} = \dfrac{{{D_{60}}}}{{{D_{10}}}} = \dfrac{{0.175}}{{0.09}} = 1.94 $$ (1) $$ {C_{\rm{c}}} = \dfrac{{D_{30}^2}}{{{D_{60}}{D_{10}}}} = \dfrac{{{{0.15}^2}}}{{0.175 \times 0.09}} = 1.43 $$ (2) -
图5为试验加载测量装置布置情况,试验过程通过水平推杆在重心位置施加水平方向的外荷载,直至模型倾覆达到极限状态,在加载过程中,通过船体顶部的倾角仪读数确保各工况下模型的加载角度相同。
采集设备采用威肯德WKD3840应变采集仪,采样频率为10 Hz。用到的传感器主要有:
1)土压力盒:用于测量桩靴表面不同位置的土压力分布,量程为0~50 kPa。
2)激光位移传感器:用于测量模型加载过程中的位移,量程为±200 mm。
3)拉线位移传感器:测量静力触探试验中桩靴的贯入深度,量程为0~500 mm。
4)倾角仪:用于确认在加载初始阶段自升式安装船的水平度,灵敏度为0.01°。
5)力传感器:量程0~300 kg,精度0.03%,用于测量加载过程中的水平荷载。
为监测自升式安装船在水平荷载作用下桩靴周围土压力变化,在桩靴模型表面对称布置了16个土压力盒,具体布置以及测点编号如图6所示,依次将桩靴命名为A、B、C、D号桩靴,其中1号和3号位于同侧,2号和4号位于同侧,每个桩靴上嵌有X-1、X-2、X-3、X-4(X为桩靴编号)4个土压计,其中,X-1和X-2位于底部,X-3和X-4位于顶部。由于自升式安装船具有对称性,文章仅对A号和B号桩靴表面土压力进行对比分析。
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为研究桩靴在不同的贯入深度下自升式安装船的极限水平承载力以及桩靴周围土压力的分布情况,设置了4种不同的贯入深度工况,如表3和图7所示。首先进行试验用土制备养护,采用落砂法将砂土均匀地洒落在土槽内,后续试验展开前需要对土槽内的砂土进行翻动,确保每次试验砂土的密实度保持相同。砂土平整后从注水管内向土槽内自下而上注水,使得水从砂土下部逐渐渗透直至越过砂土表面,注水结束后对砂土进行超过24 h的静置养护,得到完全饱和的试验砂土。为了确保每次试验的砂土相对密实度在允许的误差范围内,试验前需要对砂土进行CPT测试。
表 3 试验工况
Table 3. Test conditions
工况 贯入深度/cm 1 4 2 6 3 8 4 10 试验过程中通过水平加载杆沿船体横向进行加载,加载速度为0.27 mm/s,加载点设置在模型重心位置,试验过程中监测倾角仪读数,当安装船产生了10°倾角时,模型基本失稳,终止加载。
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文章采用ABAQUS有限元软件建立自升式安装船的三维有限元模型,如图8所示,模型与试验采取1∶1的比例建立。地基土体采用Mohr-Coulomb本构模型,其参数设置与物理模型试验保持一致。地基土体采用长×宽×高=2 m×2 m×1 m的长方体,可以忽略边界条件对试验的限制,土体底面和侧面分别施加全固定约束和水平约束,设置桩靴与土体的接触时选择刚度大的桩体作为主面、土体作为从面,桩靴与四周土体的接触方式设置为摩擦接触,基础面砂土与桩靴的摩擦系数根据参考值0.25~0.45,选择设定为摩擦系数为0.3。
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采用位移控制法来对自升式安装船进行水平加载,加载点与试验相同均位于船体模型下方8 cm处,水平加载直至基础处于极限状态。
文章参考Villalobos[20]的极限承载力确定方法来计算有限元结果。如图9所示,在位移荷载曲线弹性阶段起点和塑性阶段终点处分别作切线交于一点,然后过交点作1条水平直线与曲线相交于一点,则水平直线与曲线的交点即为基础极限状态对应的点,其对应的荷载即为自升式安装船的极限承载力。
Model Test Study on the Influence of the Spudcan Penetration Depth on the Horizontal Bearing Characteristics of Jack-Up Vessel for Wind Turbine Installation in Sandy Soil
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摘要:
目的 自升式风电安装船作为海上风电开发中的重要施工设备,研究其在位状态下的承载性能对于保障风电安装船作业安全尤为重要。 方法 文章以自升式安装船为研究对象,结合室内模型试验和有限元法开展了均质砂土中4种不同的桩靴贯入深度下的水平承载性能以及周围土压力变化规律研究。 结果 研究表明:随着贯入深度的增加,自升式安装船的水平承载力呈近似线性增长趋势,贯入深度为10 cm较贯入深度4 cm水平承载力增加了38.02%,其对应的水平位移同样呈现增加的趋势,在水平荷载作用下,桩靴的承载模式表现为临载侧桩靴受压,背载侧桩靴受拉。桩靴表面同侧土压力变化规律一致,当贯入深度为10 cm时,临载侧桩靴底的土压力变化最大值为38.37 kPa,较贯入深度为4 cm时增大了126.2%。且临载侧桩靴下表面和背载侧桩靴上表面的土压力变化较大。 结论 水平荷载作用下自升式安装船的受力模式为拉压模式,且砂土中桩靴贯入深度的增加,能显著提高水平承载性能,为保障风电安装船的安全和作业能力,需保障桩靴的贯入足够的深度。 Abstract:Introduction As an important construction equipment in the development of offshore wind power, studying the bearing performance of the jack-up vessel for wind turbine installation in the in-situ state to ensure its operation safety is of great significance. Method In this paper, taking the jack-up installation vessel as the research object, the horizontal bearing performance of the jack-up installation vessel and the variation law of the surrounding earth pressure at four different penetration depths of spudcans in homogeneous sandy soil were studied by combining with the indoor model tests and finite element method. Result The results show that with the increasing of the penetration depth, the horizontal bearing capacity of the jack-up installation vessel is on an approximate linear growth trend. The penetration depth of 10 cm led to an increase of the horizontal bearing capacity by 38.02% compared with 4 cm penetration depth, and the corresponding horizontal displacement also show an increasing trend. Under the action of horizontal loads, the bearing mode of spudcans is characterized by compression of spudcans on the loading side and tension of spudcans on the non-loading-side. The pressure change law of the soil on the surface of spudcans is the same. At the penetration depth of 10 cm, the maximum variation in soil pressure at the bottom of spudcans on the loading side is 38.37 kPa, which increased by 126.2% compared to the penetration depth of 4 cm. In addition, significant variations in soil pressure are observed on the lower surface of the loading-side spudcans and the upper surface of the non-loading-side spudcans. Conclusion Under the action of horizontal load, the force mode of the jack-up installation vessel is the tension-compression mode, and increasing the penetration depth of spudcans in sandy soil can significantly enhance the horizontal bearing capacity. Therefore, in order to ensure the safety and operational capability of the wind turbine installation vessel, it is necessary to ensure sufficient penetration depth of spudcans. -
表 1 自升式安装船试验模型尺寸
Tab. 1. Specific dimensions of the test model of the jack-up installation vessel
参数 尺寸/mm 参数 尺寸/mm 船体型长 945 桩靴高度 30 船体型宽 433 桩靴宽度 118 船体型深 76 桩靴长度 129 桩腿长度 867 桩靴中心圆孔直径 4 表 2 砂土参数
Tab. 2. Parameters of the sandy soil
参数 数值 相对密实度 0.58 弹性模量/MPa 18 粘聚力/kPa 13.2 内摩擦角/(°) 32.5 最大干密度/[g·(cm)−3] 1.50 最小干密度/[g·(cm)−3] 1.28 比重/% 2.42 渗透系数/(cm·s−1) 0.039 表 3 试验工况
Tab. 3. Test conditions
工况 贯入深度/cm 1 4 2 6 3 8 4 10 -
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