Load sharing ratios and interaction effects for piled raft foundations in sands

Abstract

In piled raft foundations, the load shared between the piles and the raft is affected by a complex soil–structure interaction. However, the number of piles and their location can be optimised, thereby making piled rafts more effective and economical. In this study, the influence of three key design parameters (the number of piles, pile length and pile spacing) on pile–pile–soil and raft–pile–soil interactions was investigated; each of these parameters can lead to improvements in the performance and efficient load sharing of piled rafts. The results of small-scale model tests in sand showed that an increase in pile number or length proportionally decreased the load taken by the raft. A change in the pile spacing or compaction state of the sand bed also affected the raft's contribution, although to a lesser extent. Load sharing between the piles and the raft was found to be not only sensitive to the foundation size but was also dependent upon its settlement. Under favourable pile–pile–soil, raft–pile–soil and pile–raft–soil interaction effects, the combined load capacity of the piled raft increased. These interaction effects were non-linear and sensitive to settlement, which resulted in non-linear sharing of the load between the piles and the raft. The effect of pile inclusion and the number of piles on the shared load was also investigated using a simple hyperbolic model while considering the above interaction effects.