A Numerical Study on the Behavior of Disconnected Composite Piled Raft, Composite Piled Raft, and Unpiled Raft under Axial Load

The unpiled raft foundation may not provide safe and economical design for highly compressible subsoil strata. The effectiveness of rafts is improved by the addition of piles as settlement reducers. However, the load distribution in piled raft is such that axial stress and bending moments are carried by the piles with minimum contribution from raft and subsoil. To mobilize the strength of subsoil in the load transfer mechanism, the concept of disconnected composite piled raft with cushion was considered. The present study aims at understanding the behavior of disconnected composite piled raft with cushion using 3D FEM analysis, by considering pile and raft as linearly elastic and non-associated Mohr-Coulomb elasto-plastic behavior for cushion and subsoil. In this study, the raft and piles were disconnected using a layer of granular material referred to as a cushion (load transfer platform). This cushion layer helped in the redistribution of the axial stress ratio amongst piles and subsoil as compared to the connected piled raft and unpiled raft. The results indicated that the bending moment, axial force, and settlements of disconnected composite piled raft were substantially modified by the cushion thickness under varying vertical pressure.