基于PIV技术的沉桩过程土体位移场模型试验研究

MODEL TEST ON DEFORMATION CHARACTERISTIC OF PILE DRIVING IN SAND USING PIV TECHNIQUE

  • 摘要: 基于粒子图像测速(PIV)技术,利用自行设计的静压桩自动沉桩模型试验系统,对沉桩过程中桩周土体位移场进行测量。在沉桩过程中,利用CCD(charge coupled device)高速工业相机连续拍摄试验观测面上桩周土体变形的灰度图像,然后对初始点和峰值点进行分析,得到位移场分布。研究了不同沉桩深度、桩-土摩擦系数和桩尖形式情况下沉桩对周围土体位移场的影响规律;相应试验结果与圆孔扩张理论解进行对比分析,其径向位移变形的规律基本一致,验证了模型试验的可靠性。相对常规试验方法,该试验操作简便,对环境要求不高,可以进行非插入式全场测量。研究结果表明:在该文试验条件下,对于平底圆桩,沉桩过程对桩侧土体位移影响范围在8R附近,对桩端底部土体影响范围在4R附近;桩身摩擦的存在使得桩侧向土体位移影响范围增大2R左右,对桩端底部土体位移基本没有影响。当桩尖角度由0°变化为45°时,桩侧的水平和竖向位移均增大,桩端底部的竖向位移明显减小;而桩身摩擦对其水平位移和竖向位移影响不大。

     

    Abstract: A small-scale modeling test system based on particle image velocimetry (PIV) was developed for studying the movement of soil during a pile installation. During the whole process, a charge coupled device (CCD) camera was used to capture images of planar soil deformation. Using PIV, the displacement distributions during a pile installation were then obtained, considering different jacking depths, frictions and pile shoes. The observed displacements were compared with the theoretical predictions of a cavity expansion method, and the law of radical displacements were similar. Thusly, the test system is valid. Comparing with the traditional test methods, it is easy to operate and the non-intrusive technique has a low request to its environments. The test results showed that for a flat-ended pile, its influence zone was 8R around the pile shaft and 4R below the pile tip; when shaft friction was considered, the observed influence radius was 2R larger around the pile shaft but has little effect below the pile tip. Meanwhile, for a pile with a shoe angle of 45°, the displacement around the pile shaft was higher, but the vertical movement below the pile tip was much lower, compared with the flat-ended pile; when shaft friction was considered, the observed displacement was almost identical.

     

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