Analysis of interaction of piled raft and foundation considering both effects of soil rheology and foundation consolidation

It has been clarified that the time-dependent behavior of soil results from both rheological properties of soft soils and consolidation of foundations which display a certain nonlinear characteristics and will play an important role in performance of major structures on soft soil grounds. In this paper, the time-dependent effects of soil deformation on interaction behavior of piled rafts and soil are considered. In the proposed procedure, the Biot's fully coupled equations of consolidation are numerically solved by finite element method; and an elasto-viscoplastic (EVP) model of soils is employed to consider the rheology of soils. The variations with time and distribution in space of excess pore pressures in foundation soil underlying the piled raft and reactions as well as deformations or settlements of raft and piles during loading are examined through numerical analysis. It is shown that the coupled behaviour of rheology and consolidation of soils remarkably affect time-dependent performance of interaction of piled rafts and soils and the dissipation of excess pore pressures not only displays the Mandel-Cryer effects, but also is intimately associated with rheological deformation of ground especially in poor drainage condition. The pore-water pressure predicted considering rheological effect in addition to consolidation displays different patterns from those obtained by conventional consolidation analysis without consideration of soil rheology. While both effects of rheology and consolidation are taken account, the rigidity of piled raft plays a significant role in governing variation modes of reactions and deformations of piled raft with time. Furthermore, the edge pile displays different time-dependent behavior of internal forces and deformations from those of the central piles. The skin friction of pile may also display the nature of time-dependency. During loading, negative skin friction may occur in the pile segments near ground surface under soft soil condition and cannot be negligible in engineering design. The coupled analysis of rheology and consolidation gives rise a more rational evaluation of overall performance of interaction of piled raft and subsoil and conventional analyses which overlooks time-dependency of soil deformation may cause a certain inaccuracy in evaluation of interaction behavior and unreliability in design of structures on piled raft and foundation.