Numerical study on settlement-dependent variation of raft-soil-pile interactions for large piled raft in clay soil

Abstract

In a piled raft foundation, the stresses applied on the soil from the raft and piles overlap, which leads to changes in the settlement and bearing capacity of the raft and each individual pile. In this numerical study, settlement-dependent variation of three interaction factors, namely piles-to-piles (P-P), raft-to-piles (R-P), and piles-to-raft (P-R) have been investigated for large piled raft in stiff clay. The unpiled raft is flexible, the piles are friction piles and the effects of pile number, spacing and length on these interaction factors are presented. The P-P factor increases and then tends to become constant at a certain settlement. In contrast, the R-P factor always shows an increasing trend with settlement. However, the P-R interaction factor initially decreases and then increases with settlement. At the final settlement equal to 0.35% of raft width, the P-P, R-P, and P-R interaction factors range from 0.95 to 1.10, 0.86–1.04, and 0.25–0.92, respectively. Predictive equations have been proposed for these interaction factors and thereby determine the load-sharing ratio and mobilized safety factor. Within the allowable settlement range satisfying the serviceability limit, a good agreement between the results obtained from predictive equations and the finite element analyses is demonstrated for different piled raft configurations.