Analysis of Piled Raft Foundations in Clayey Soils using Finite Element and Analytical Methods

Raft foundations are usually used as a foundation on soft or variable ground for commercial, industrial or residential building. They have the advantage of providing the adequate bearing capacity and also reducing differential settlements of structure. Unfortunately, raft foundation may cause excessive settlement although it has an adequate bearing capacity. Considering that foundation building must have adequate bearing capacity but the total or differential settlements of the foundation should not exceed the allowable value, the combination of raft and pile foundation as named piled raft foundation system may be considered as the good alternative solution for this problem. The contribution of a group of pile under raft could acts as a settlements reducer.
This study analysed the settlement of piled raft foundation by considering the various number of piles using finite element method and analytical method. In this study, the finite element method were conducted using a PLAXIS-2D software and the analytical method was carried out using simplified calculation method by Poulos and Davis.
In order to obtain the appropriate comparison of piled raft settlement for both methods of analysis, it might be used a parameter called settlement reduction factor, since a number of piles in piled raft system acts as a settlement reducer. Both methods also performed that addition of piles beyond the optimum number of piles does not have significant effect in the reduction of piled raft settlement. So, for economic design, it needs to determine the optimum number of piles based on the allowable settlement. In this case study, by considering the settlement reduction factor, both methods of analysis showed the optimum number of piles in this piled raft system is approximately 15 x 15 piles.