Finite Element Analysis of Piled Raft Foundation System

The piled raft foundation system, which combines raft and pile foundations, addresses potential excessive settlement despite sufficient bearing capacity by having piles control settlement. In contrast, the raft bears the superstructure's load. Settlement behaviors of these foundations were analyzed using a 15-noded plane strain model in PLAXIS 3D. Factors such as raft thickness, length of pile, spacing between piles, and number of piles were studied to determine optimal design parameters, including the best pile location. The soil and piles were modeled with solid finite elements, and the raft was represented using first-order shell components. Nonlinear soil behavior was modeled using a cap model with three yield surface segments. Contact zones between soil and raft, and soil and high-diameter drilled piles, were represented using thin solid continuum elements. The raft and piles have been assumed to act linearly and elastically. In-situ subsoil conditions comprised Frankfurt clay overlain by Frankfurt limestone, simulated using an elastoplastic cap model. Young's modulus distribution of Frankfurt clay with depth has been considered nonlinear in PLAXIS modeling, with parameters chosen from stacked raft system elements. It has been observed that increasing the concentration of piles around the center of a uniformly loaded piled raft foundation of a rectangular plan reduced differential settlement. While adding piles reduced settlement, increasing their number beyond a certain threshold had no effect in further settlement reduction. Stiffnesses of both raft and pile group elements significantly influenced total and differential settlement in piled raft systems. Additionally, increasing the raft thickness up to 2 m substantially reduced settlement compared to shallow raft foundations.