Large scale model testing to investigate the influence of granular cushion layer on the performance of disconnected piled raft system

Abstract

This paper presents the results of 1g model tests performed on instrumented model foundations, i.e., unpiled raft, single piled raft, single disconnected piled raft (DPR) and 3 × 3 DPR in sand under vertical load by using different granular materials and thickness of the granular cushion layer to investigate the effects of granular cushion on the performance of DPR system. The Settlement Efficiency (η) of the DPR which is nonlinear in nature is found to increase as the cushion thickness decreases and the mean particle size (d50) of the cushion material increases. A cushion thickness of two times the pile diameter and cushion material having d50 more than or, equals to 2 mm might serve as the suitable cushion material for the optimum performance of 3 × 3 DPR. The neutral axis and the zone of occurrence of maximum axial load of the pile in DPR are found to move downward with increasing cushion thickness. The piles in DPR are found to carry 35% of the total superstructure load within the settlement range considered in the study.