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.