Study On Character Of The Piled Raft Foundation

As a new philosophy of using piles as settlement controller, Piled raft foundation provides an economical foundation option for circumstances where the performance of shallow foundation doesn't satisfy the design requirement. As limited cognitive level, civil engineers still use traditional methods to design piled raft foundation. However, some engineers begin to analyse the pile-soil-raft interaction recently. This paper gives some research on the analysis of piled raft foundation subjected to vertical loadings.The character of some piles, maybe all the piles, in piled raft foundation is nonlinear, so elastic theory can not be used to calculate the settlement of piled raft foundation. Poulos-Davis-Randolph (PDR) Method is a empirical calculation method. It is easy to compute the relation between the number of piles and the average settlement of the foundation. A new design method is brought forward based on the PDR methods. The modified PDR Method develops a tri-linear load-settlement curve. The non-linearity of the foundation can be analysed by the factor of the raft-pile interaction. Moreover, a factor behaviors of over consolidated soil is used.The piled raft foundation belongs to large spacing pile foundation. Each pile works similarly as single pile. A complete three-dimensional analysis of a single pile is carried out by finite element analysis. The contact element will be used in order to model the pile-soil interface. The three-dimensional model of piled raft foundation is created. The result of analysis can be used to show the effect of the raft thickness, pile stiffness, Young's modulus of soils and the number of piles.The modified PDR method is used to design a practical projects. Although the calculated average displacement of the building is less than the actual measurement. It is acceptable.