A Numerical Study of Performance of Large Piled Raft Foundation on Sand Under Vertical Loading

Abstract

3D finite element analyses were conducted to understand the performance of large piled-raft foundations on sand by considering the influence of geometric parameters like the spacing and length of piles, and thickness of raft on differential and average settlements, bending moment and load sharing ratio. The piled-raft with 4 × 4 pile configuration and pile length and pile spacing varying from 20 to 50 and 4 to 16 times the pile diameter, respectively, were considered for the study. The raft thickness was varied such that its stiffness ranged from extremely flexible to extremely rigid case. It is observed that for all the considered pile lengths, with increase in spacing of pile, differential settlement initially decreases and attains a minimum value, and thereafter, it increases. For any pile length, the change in average settlement with pile spacing is negligible. The increase in the load sharing ratio with increasing pile length is not found to be significant for higher pile lengths. For thicker rafts, the differential settlement becomes negligible at all pile spacing. However, for lower raft thickness, differential settlement initially reduces for lower pile spacing and then increases for higher spacing of pile. For lower spacing of pile, the average settlement increases with increase in thickness of raft, whereas for higher spacing of pile, there is no significant change in average settlement with variation in raft thickness. With increase in the thickness of raft, raft bending moment increases but it does not affect the load taken by piles significantly.