Study of Scale Effect of Piled Raft Foundations in sand under compression load

Raft foundations usually have a high bearing capacity in sand, but the amount of settlement limit the allowable bearing pressure. Nowadays, the employment of piled rafts foundations as a solution for decrease of settlement is common. In such cases, the raft usually carries a high portion of structural loading, and the piles are as the settlement reducer elements. The number of piles and their configuration are determined that settlement of the foundation decreases to an allowable value. In these situations, the configuration of piles is determined in optional manner and strategically. In a piled raft foundation, pile-soil-raft interaction is complicated. Although several numerical studies have been carried out to analyze the behaviors of piled raft foundations, very few experimental studies are reported in the literature. This paper concentrates on study of behavior of piled raft in sand by physical modeling and finite element analysis method. The piles and raft models were made of cast-cast-in-place concrete. The physical models consisted of single pile, single pile in group, unpiled raft and piled raft foundation. The size effects of the models were investigated. The results showed that with installation of the single pile in the group, the pile bearing capacity and stiffness increase. Due to increase of the number of piles beneath the raft, the bearing capacity of raft increase and its settlement decrease, significantly. With the use of finite element method and the critical state theory, one can predicate behavior of test model in the full scale dimensions.