Experimental assessment of the performance of cushioned disconnected piled raft system

This paper presents an experimental investigation revealing the effects of key design parameters on the behavior of disconnected piled raft (DPR) system. Large-scale model tests are conducted on instrumented foundations by varying the pile spacing, pile length, and the cushion thickness. From the test results, the load capacity improvement (LCI) factor of 3 × 3 DPR is found to increase with increasing pile spacing and length and decreasing cushion thickness. Interestingly, this factor is found to be higher at lower settlement of the raft irrespective of the length and spacing of the piles. The maximum axial load in a pile is found to occur 0.25 m below the pile head due to the generation of negative skin friction in the shallow depth. A significant downward shift of the neutral axis of the pile is observed with increasing cushion thickness resulting a higher difference between the pile head load and maximum axial load. The average load proportions of the piles and the raft in a DPR system are found 31% and 69%, respectively, when the raft settlement reaches 10% of its width. Based on the quantitative impact of these design parameters, recommendations are also provided regarding the design of the DPR system.