The piled-raft behavior installed in unsaturated collapsible soils

Abstract

Pile-raft foundation has been used to increase the bearing capacity of pile group. Most of the studies have been conducted on the pile group, and the effect of pile cap on the bearing capacity is largely neglected. The pile cap system plays an important role in increasing the bearing capacity of the cap group constructed on collapsible soils. In the present study, the collapsibility effect on settlement of pile-raft foundation based on water content and cap rigidity was taken into consideration using experimental procedures. These experiments were carried out on pile-raft, pile group, single flexible cap, and single rigid cap at different water contents. The results revealed that in unsaturated soils, increasing the water content led to decreasing the bearing capacity of the pile-raft system. Furthermore, in the saturation state, the portion of raft effect is negligible and the loads are completely tolerated by piles. The results also showed that decreasing the soil water content increased the efficiency of rigid and flexible cap, pile-raft, and free pile group. Moreover, the efficiency of the rigid pile-raft system is more than that of the flexible system, and the difference is insignificant when the water content reaches to saturation status. Finally, at similar water content and stress, the settlement of the flexible pile-raft system would be greater than that of the rigid pile-raft system.