Long-term behavior of piled raft foundation models supported by jacked-in piles on saturated clay

As the demand for using piled raft foundations (PRFs) on clayey grounds increases, so the need arises to understand their time-dependent behavior. This is because the stresses and strains in clayey grounds change for a long time after the completion of the construction work due to ground consolidation. For a better understanding of this behavior, the present paper used small-scale physical modeling to investigate the long-term behavior of two vertically loaded PRF models on saturated clay. In the experiments, the model ground was prepared by consolidating a slurry clayey mixture. Each of the model foundations comprised a square raft and four piles with different pile spacings. The applied load, PRF deformation, axial forces along the piles, pore water pressure (PWP), and earth pressure beneath the raft base were measured. The results show that the piles were effective at suppressing the PRF settlement when the applied load was less than 70% of the piles' ultimate estimated capacity. In the primary consolidation stages, the pile resistance increased with time especially at the top sections because of the PWP dissipation and the corresponding increase in the effective soil stresses below the raft base. In the secondary consolidation stages, both the raft and the pile resistances were stable even though creep settlement had continued. When the applied load was larger than 50% of the PRF predicted capacity, the PRF with the narrower pile spacing suppressed the settlement better than the PRF with the wider pile spacing. The study involved small-scale experiments; however, it emphasized the importance of considering the interaction among the piles, the raft, the ground, and the PWP. (C) 2020 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.