为探究海上风力机液压锤击沉桩机理,通过采用光纤光栅（FBG）应变传感器和薄膜压力传感器等监测技术,在砂土中开展开口钢管桩（直径D=0.273 m）液压锤击沉桩的大比尺（1∶10）模型试验,砂土密实度为70%。研究沉桩过程中土塞高度、桩身残余轴力和侧摩阻力、桩土界面应力以及砂土中应力场变化规律。研究结果表明：FBG应变传感器能在高能的液压锤击沉桩中存活,并能有效监测动态荷载下的桩身应变;在沉桩过程中最大的冲击加速度达到100g,FBG应变传感监测到最大桩身应变为450×10-6;随着沉桩深度的增加,土塞率变化不大,土塞增长率（IFR）值接近1,土塞效应不明显;桩尖和桩侧处法向应力随h/R增加而降低（其中h为监测点离桩尖的高度,R为桩半径）,并且桩侧法向残余应力显著小于锤击时的法向应力;沉桩过程中,靠近桩尖的土体应力急剧增加,随后逐渐减小并趋于稳定,并且表现为“径向应力>竖向应力>环向应力”的应力分布特征,同一水平面,距离桩越远土体应力越小。在刚度和变形控制严格的海洋桩基中,需要考虑沉桩效应的影响。
Abstract
Offshore wind turbine pile foundations are primarily constructed using open-ended pipe piles, which are driven into the ground using hydraulic hammer, This construction method leads to changes in the stress and displacement fields of both the pile body and the surrounding soil. These changes occur due to the large diameter of the pile and the high energy used during the penetration process. In order to investigate the mechanism of hydraulic hammer driving of offshore wind turbine piles, a large scale （1∶10） model test of hydraulic hammer driving of open-ended steel pipe piles （diameter D=0.273 m） was carried out in sandy soils with 70% densification by adopting the monitoring techniques of fibre-optic grating （FBG） strain transducers and thin-film pressure transducers. The study focused on the variation of soil plug height, pile axial force, and lateral friction resistance, pile-soil interface stress, and stress in sand during pile driving. The results show that the FBG strain sensor can withstand high-energy hydraulic impact during pile driving, and effectively monitor strain changes in steel pipe piles under dynamic loading. The maximum impact acceleration reaches 100 g during installation, and the maximum strain of the FBG sensor was 450×10-6. With an increase in pile driving depth, there is little change in the Plug Length Ratio （PLR）. The Incremental Filling Ratio （IFR） value is close to 1, indicating that the soil plugging effect is not significant. The normal stress at the pile tip and the side of the pile decreases with the increase of h/R（where h is the height of the monitoring point from the pile tip and R is the pile radius）. Additionally, the normal residual stress at the pile side is significantly smaller than the normal stress during vibration. During the process of pile driving, the soil stress experiences a sharp increase as the pile tip approaches. This stress gradually decreases as the pile passes through the soil, and eventually stabilize. The principal stress distribution during this process follows the pattern of "radial stress > vertical stress > circumferential stress". At the same level, the farther away from the pile, the smaller soil stress. Therefore, it is necessary to consider the effect of pile driving on the marine pile foundation with strict stiffness and deformation control.
关键词
近海风力机 /
液压锤击 /
开口管桩 /
FBG应变传感器 /
土塞效应 /
桩土界面应力
Key words
offshore wind turbine /
hydraulic vibration /
open pipe pile /
FBG strain sensor /
soil plugging effect /
pile-soil interface stress
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基金
国家自然科学基金（52020105003; 52208343）; 江西教育厅科技项目（GJJ2205202; GJJ2905306）
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