Comparative Analysis of Axial Load Capacity for Piled-Raft Foundation with Changes in Groundwater Level

Groundwater affects the load carrying behavior of foundations as the effective stress changes with the location of groundwater level (GWL) where the non-linear variations in stiffness and strength and the GWL influence zones below the foundation are involved. In this study, the load-settlement curve and the axial load capacity of piled-raft foundation with changes in GWL was investigated based on the results obtained from the finite element (FE) analyses. The full depth range of GWL from the top soil surface to the depth of well-below pile base was considered in the FE analyses. Changes in the effective stress and state-dependent soil stiffness with GWL were quantitatively evaluated and considered. It was found that the axial load capacity changed most significantly for GWL depths from 0 to 1.0 times the raft width, indicating that the GWL influence depth for piled rafts is controlled by raft size. The GWL effect factors for the load capacity (C_w) and settlement (S_w) of piled rafts were proposed. It was found that the values of S_w were larger than for unpiled rafts. The maximum value of S_w for piled rafts was 1.55 for GWL at the top surface, which decreased logarithmically with increases in the depth of GWL. The correlation of S_w to GWL was proposed.