Model tests on pipe pile penetration by using transparent soils

The squeezing effects of open-ended and closed-ended pipe piles are obviously different because of “soil plug”. However, the researches focused on this problem are relatively little. One small-scale model test system is developed to study the non-intrusive measurement of the soil deformation during pile penetration using the transparent soils and PIV (particle image velocimetry) technique. The transparent soils are manufactured by baked quartz with a pore fluid which has the same refraction index. The test system contains a line laser light, a CCD (charge-coupled device) camera, a loading machine and a computer. The whole displacement field during the pile penetration can be obtained as follows: a distinctive laser speckle pattern can be generated by the interaction between the laser and the transparent soils when the light goes through the transparent soils. Then a sequence of speckle pattern images are captured consecutively during the pile penetration by the CCD camera. Finally these images are analyzed by using PIV. The model tests on the penetration of an open-ended pipe pile and a closed-ended pipe pile are both carried out, and the data are compared with the results obtained by the cavity expansion method and strain path method. The results show that, for the closed-ended pipe pile, the radical displacements obtained by the model tests are smaller than those by the cavity expansion method, and are close to those obtained by the strain path method; for the open-ended pipe pile, the “soil plug” obtained by the model tests is larger than that obtained by the cavity expansion method.