An Analytical Study of Piled Raft Foundations: Design and Applications | Original Article

ABSTRACT:

The design concepts given by various researchers on pile-raft foundation is reviewed and described in this paper. It was found out that connected pile raft foundation (CPRF) helps in reducing differential settlement and to some extent overall settlement by locating piles strategically beneath the raft. Unconnected pile raft foundation (UCPRF) as described by Al Ataa et al is also reviewed. He observed that cushion helped in distribution of load beneath the raft. Favorable conditions for UCPRF are similar to that of CPRF. But UCPRF was found relatively less effective (depending on different conditions) foundation system. Author proposes a future scope of combination of CPRF and UCPRF as effective and economical foundation system. In situations where a raft foundation alone does not satisfy the design requirements, it may be possible to enhance the performance of the raft by the addition of piles. The use of a limited number of piles, strategically located, may improve both the ultimate load capacity and the settlement and differential settlement performance of the raft. This paper discusses the philosophy of using piles as settlement reducers and the conditions under which such an approach may be successful. Some of the characteristics of piled raft behaviour are described. The design process for a piled raft can be considered as a three-stage process. The first is a preliminary stage in which the effects of the number of piles on load capacity and settlement are assessed via an approximate analysis. The second is a more detailed examination to assess where piles are required and to obtain some indication of the piling requirements. The third is a detailed design phase in which a more refined analysis is employed to confirm the optimum number and location of the piles, and to obtain essential information for the structural design of the foundation system. The selection of design geotechnical parameters is an essential component of both design stages, and some of the procedures for estimating the necessary parameters are described. Some typical applications of piled rafts are described, including comparisons between computed and measured foundation behaviour.