基于透明土材料的沉桩过程土体三维变形模型试验研究

为了对沉桩过程中桩周土体内部的变形特性进行非插入式测量,利用正十二烷、十五号白油混合液和玻璃砂合成透明土,并在此基础上设计了沉桩模型试验系统；该系统包括激光器、线性发生器、CCD（charge-coupled device）相机、沉桩加载仪和计算机等。激光经线性发生器转化后将透明土样切分,形成土体内部颗粒切面,CCD相机连续拍摄沉桩过程中该切面的图像,并通过计算机中图像处理软件进行分析,得到该切面变形前后的变形位移场。通过与数值模型的对比分析,验证模型试验结果的可靠性。对多个切面变形前后的位移场进行分析,从而得到沉桩过程中土体变形的完整三维变形场。试验结果表明,试验条件下沉桩水平挤土位移影响范围为8R；与常规模型试验方法相比,方法实现了土体内部变形的三维测量,有助于了解土体在各种荷载条件下的变形机理。

Model tests on 3-D soil deformation during pile penetration using transparent soils

In order to meet the need for nonintrusively measuring the spatial deformation pattern in soils during pile penetration, the transparent soils made of glass sand and pore fluid with a matching refractive index are used. A small-scale laboratory modeling test system is designed. The system consists of a laser, a linear generator, a charge-coupled device (CCD) camera, a loading frame and a computer. A distinctive speckle pattern is generated by the interaction between the laser light and the transparent soils. A sequence of laser speckle images are recorded during pile penetration. They are then analyzed using the image processing technique, and the complete 2-D displacement field is obtained. By combining the multiple slices of 2-D displacement fields, a 3-D displacement field is obtained. The observed horizontal influence zone is 8R from the pile shaft. The results show good agreement with the theoretical predictions of numerical method. Compared with the traditional test methods, the proposed system is more suitable for more advanced 3-D soil deformation measurements and can be employed to study the deformation mechanism of soils.