An investigation on reinforcement of cushion with geogrid in non-connected pile raft foundation resting on loose sandy soils adjacent to the coastal area

In the coastal areas and especially in the harbors, due to the presence of loose sandy sediments and structures under high lateral and vertical loads, the use of pile raft is a suitable choice for the foundation of these infrastructures. In this system, raft and piles are separated and a cushion is used in the distance between the raft and the piles. The existence of reinforcement layers in the cushion such as the geogrid changes the behavior of the pile raft system. In this paper, the behavior of reinforced nonconnected pile raft with geogrid under vertical loading in sandy soils has been investigated by a laboratory studies. An automatic hydraulic jack were used in the load application and LVDT is used to measuring the settlement. The strain gages are installed at the tip of the piles to calculate the force applied to the piles. Tests were carried out under reinforced and non-reinforced condition. In non-reinforced case, the optimum thickness and pile spacing of the cushion and in the reinforced case, the optimal location of the first and second layer of the geogrid and the effect of the geogrid layers length on the load-settlement behavior and the share of the piles from the total load were evaluated. The results shows that the thickness of the cushion and the pile spacing have a significant effect on the behavior of the pile raft. The presence of geogrid layers in the cushion increases the bearing pressure and the share of piles from loads.