Effectiveness of rolling dynamic compaction with a three-sided compactor on unsaturated sand

As a widely applied ground improvement technique, rolling dynamic compaction (RDC) densifies the soil by imparting a combination of kinetic and potential energy into the ground. In previous studies on RDC, attention has been paid to the stress distribution, soil particle movements, depth of influence, density increases etc. beneath the soil surface. However, the influence of the moisture contents and water table in unsaturated soils on the effectiveness of RDC remains uncertain. To better understand the performance of RDC on unsaturated soils, 6 laboratory experiments were conducted on Sydney sand with a 1:10 scale 3-sided impact roller. The roller has a mass of 46 kg and was towed at a constant velocity of 1.5 m/s in each test. Settlements at different depths beneath the surface were measured by buried plastic plates and particle image velocimetry (PIV) was applied to track the movements of the soil particles. Penetration tests were conducted before and after each experiment to assess the increases in the soil density. Measurements show that the depths of influence (DOI) for unsaturated sand were from 200 mm to 300 mm, however, density increases of less than 2 % were reported in all cases below the depth of 100 mm. These results, after compared with results of dry sand, demonstrates a negative influence of the moisture and water table on the effectiveness of RDC. The results from PIV suggest that the translational motion of the roller is transferred to a deeper level due to the tensile strength developed in unsaturated sand.