Behaviour of piled rafts with piles of different lengths and distributions under vertical loading

The pile-raft foundation is a combination of a raft foundation with piles. Pile-raft foundation has been widely designed, assuming all structure loads to be transferred to piles without considering contribution of the load taken by contact surface between raft and soil. Methods of analysis currently used in practice are based upon relatively conservative assumptions of soil behaviour or on the less realistic soil-structure interaction. In this study, a nonlinear three dimensional finite difference analysis was carried out to model the piled raft problems using the commercial software FLAC3D. The validity of the numerical modelling procedure performed by the authors was checked by making back-analysis for an actual case study. A comprehensive parametric study was performed on a hypothetical square piled raft over clay soil profile. The variation was made in number of piles, length of piles and distribution of piles over the raft area. The variables were studied in terms of their effect upon the average settlement, differential settlement, and load sharing between piles and raft. Finally, some selected cases from the parametric study were resolved using different type of link between the pile tip and the soil. The results of the resolved cases were compared with those of the original cases to assess the effect of changing link type at the pile tip on the different variables.