This paper presents an improved solution algorithm based on Finite Element Method (FEM) to analyze piled raft foundation. Piles are modelled as bar elements with soil springs. Finite element analysis of raft is based on the classical theory of thick plates resting on Winkler foundation that accounts for the transverse shear deformation of the plate. Four node-isoparametric rectangular elements with three degrees of freedom per node are considered for the development of finite element formulation. Independent bilinear shape functions are assumed for displacement and rotational degrees of freedom. The effect of raft thickness, soil modulus and load pattern on the response is considered. Significant improvement in the settlements and moments in the raft is observed.

Piled raft foundations for important high-rise buildings have proved to be a valuable alternative to conventional pile foundations or mat foundations. The concept of using piled raft foundation is that the combined foundation is able to support the applied axial loading with an appropriate factor of safety and that the settlement of the combined foundation at working load is tolerable.

In a piled raft foundation, the total load coming from the superstructure is partly carried by piles through skin friction and the remaining load is taken by raft through contact with the soil. In conventional piled foundation, it is assumed that the raft does not carry any load even if the raft is in contact with the ground. Also, in conventional piled foundation, as the contribution of raft is ignored, long piles are provided, which extend up to the deep hard strata. On the other hand, if raft only has to carry the total load coming from the superstructure, very thick raft is needed, which increases the cost of the foundation. Such raft foundation undergoes excessive settlement. In such a condition, piled raft foundation can be considered a best solution in which shorter piles and raft of lesser thickness can be provided.

Structural Engineering Journal, Piled Raft Foundation, Finite Element Method, FEM, Four Node-Iisoparametric Rectangular Elements, Conventional Pile Foundations, Mat Foundations, Finite Element Analysis, Winkler Foundation, Raft Foundation System, Finite Element Formulation, Soil Modulus.