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在桩基负摩阻力的研究中桩土位移需重点关注。作为一种成熟的流场测试手段,颗粒图像测速(paticle image velocimetry,PIV)技术已逐步推广至岩土研究领域,将该技术运用至桩基负摩阻力模型试验,可以弥补传统位移测试方法无法获得位移场分布等缺点。基于试验特点,设计由钢板和有机玻璃壁组成的试验箱,采用千斤顶配合置于土表的载荷板实现对土体加载。试验中,对不同土表超载作用下的土体分层沉降、桩身沉降及轴力进行测定,采用PIV技术对桩端处砂土的位移场实施了采样分析。试验表明,PIV所测位移数值与传统方法测得值吻合较好,PIV分析结果能够直观反映桩基受负摩阻力作用而产生的附加沉降;并且可以判断桩端沉降的影响范围,深度方向基本不超过1.75D(D为直径),水平方向则基本在桩底边界范围内。最后,总结了PIV技术在模型试验中的运用,提出了几点在今后试验中可待改进的地方。
In the study of negative friction of pile foundation, the displacement of pile and soil should pay more attention. As a mature method of flow field testing, the technique of particle image velocimetry (PIV) has been gradually extended to the field of geotechnical research. Applying this technique to the negative friction model test of pile foundation can make up for the failure of traditional displacement testing methods Obtain the displacement field distribution and other shortcomings. Based on the characteristics of the test, a test chamber composed of a steel plate and an organic glass wall is designed, and a jack is used to load the soil with a load plate placed on the earth surface. In the experiment, soil subsidence, pile settlement and axial force under different soil surface overloading were measured. The PIV technique was used to carry out sampling analysis on the displacement field of sand at the pile tip. The experimental results show that the measured values of PIV are in good agreement with the values measured by the traditional method. The results of PIV analysis can directly reflect the additional settlement caused by the negative friction resistance of pile foundation. And the influence range of pile settlement can be judged. The basic depth direction Not more than 1.75D (D is the diameter), the horizontal direction is basically within the boundary of the bottom of the pile. Finally, the application of PIV technology in the model test is summarized, and some points that can be improved in the future test are put forward.