Experimental study on the performance of a model piled raft foundation under various suction conditions

Groundwater level fluctuations caused by seasonal variation or climate change modify soil suction, affecting the performance of foundations in unsaturated soils. However, their influence on the bearing capacity and load-sharing behaviour of pile raft (PR) foundations remains insufficiently understood. This study conducted model tests on PR foundations in sand under different initial suction conditions and during suction reduction under a dead load. Soil suction was uniformly controlled using the hanging water column technique with a microporous membrane filter. Vertical load tests were performed on unpiled raft (UR), pile group (PG), and PR models under different initial suction conditions, followed by suction reduction tests on UR and PR under a dead load. Results show that although initial suction affected each foundation differently, PR foundations exhibited greater robustness to suction changes, and the PR efficiency factor converging to approximately 77%. These findings highlight the need to consider both suction-induced soil strengthening and collapse effects when evaluating PR performance in unsaturated ground.