Ratio of long-term settlement to immediate settlement for piled raft on soft clay

A simplified analytical approach based on the non-linear pile–soil interaction model under vertical load is employed to analyse settlement of piled raft foundations. The accuracy of the simplified method is verified through comparisons with the results from previous research. Furthermore, according to the calculation results of various pile configurations, a simple empirical equation for estimating long-term settlement of a piled raft foundation is proposed. The prediction equation is validated through comparison with published cases. The comparison results show that the ratio of long-term settlement to immediate settlement increases linearly with the square root of the number of piles (at the same pile spacing), whereas the influence of the length/diameter ratio of the pile is small. The settlement ratio is approximately 2 for a piled raft foundation, and 1·5 for a raft or box foundation, and this may be useful for preliminary assessment of the long-term settlement behaviour of piled raft foundations.