A hydraulic gradient similitude testing system for studying the responses of a laterally loaded pile and soil deformation

In this study, a newly developed hydraulic gradient similitude (HGS) test and the particle image velocimetry (PIV) technique were applied to a laterally loaded pile to simultaneously measure the responses of a laterally loaded pile and sand displacement fields in a high-body force field. A comparison of the stages in the HGS test indicated that the lateral displacement of the loading point was doubled and that the applied load increased by 54 %. These results indicate that the rate of load increase gradually decreases with the increased displacement due to the plastic behavior of the soil. In addition, soil deformation increased as the lateral load increased, the soil behind the pile moved downwards because the resistance of the pile decreased, and the soil near the ground in front of the pile moved upwards because the movement of the pile caused the soil to resist lateral movement. The authors provide an additional model test for saturated soils under hydrostatic conditions (i.e., 1 g) to study the effects of the hydraulic gradient on the response of the pile and sand deformation. This comparison indicated that the lateral load in the HGS test was 4.2 times greater than that in the 1 g model test with a displacement of 3.82 mm times the loading point. In addition, the magnitudes of the deflection were smaller than those in the 1 g model test when the self-weight stress was increased 11 times. The passive influence zone in front of the pile in the 1 g model test was 50 % greater than that in the HGS test. In addition, the sand displacement around the pile in the 1 g model test was greater than that in the HGS test. The main reason for the abovementioned results are that the relative stiffness ratio between the soil and pile increased as the hydraulic gradient increased. Ultimately, this study shows that the PIV technique can be used to accurately measure soil displacement and represent pile deflection under different body forces. This study increases our understanding of the responses of soil to a laterally loaded pile and of soil deformation in a high-body force field. The results of this study demonstrate that the developed HGS device and the combination of the HGS and PIV techniques are suitable for solving soil-pile interaction problems.