Groundwater-Induced Settlements of Group Piles in Sand through Rising and Falling Phases of Groundwater Fluctuation

In this study, the settlement behavior of group piles installed in sand under various conditions of groundwater level (GWL) was investigated in comparison with that of a single pile. An experimental program with centrifuge tests was prepared, specifically designed to simulate fluctuating GWL, and adopted to investigate GWL-induced settlement of group piles. From the centrifuge tests, it was shown that the settlement of group piles caused by fluctuating GWL was 60.9 mm, which was larger than that of a single pile, 27.5 mm, indicating that the effect of fluctuating GWL was more significant on group piles. The GWL-induced settlement during rising GWL was larger than during falling GWL. The difference in settlements of group to single piles was largest during the first GWL fluctuation and decreased with repeated GWL fluctuation and increasing load level. From the particle image velocimetry analysis, it was shown that the effect of GWL fluctuation was significant in a highly loaded zone. The finite-element (FE) analysis was performed to investigate the group effect on the settlement according to the depth of GWL. The group effect was more significant at a lower load level and greater depth of GWL. The group-to-single pile settlement ratio for the condition of fluctuating GWL was larger than for that of a fixed GWL, while both decreased with increasing load level.