Load transfer mechanism for connected and disconnected piled raft: a comparative study

This paper presents a comparative experimental study highlighting the differences in load transfer mechanism between the connected and disconnected piled raft systems. Scaled physical model tests are performed on instrumented foundations embedded in sand under vertical load. Results suggests that the connected piled raft (CPR) shows higher settlement efficiency than disconnected piled raft (DPR) system. The thickness of the cushion layer in DPR is found to play crucial role in defining the load transfer mechanism that is different from the CPR. Unlike CPR, the maximum axial load on pile in DPR does not occur at the pile head but at a depth equals to 10 times the pile diameter below from the pile top due to the generation of negative skin friction in the upper part of the pile. In DPR, the raft takes the majority of load initially and then the pile load proportion increases gradually which is exact opposite to the CPR phenomenon. A progressive reduction in the axial load on the pile in DPR is observed with increasing cushion thickness. The piles in CPR basically act by reducing the raft stiffness, whereas, in DPR, settlement-reducing disconnected piles act primarily as soil reinforcement by enhancing the raft stiffness.