Contribution to the design methodologies of piled raft foundations under combined loadings

Abstract

Although simplified design methods for piled raft foundations have been proposed to allow for the group effect and soil–pile–raft interaction, most of them are concentrated on one type of loading, rendering the applicability of these methods limited to cases under such loads. In the case of a combined pile raft foundation (CPRF), the structural loads are carried partly by the piles and partly by the raft as a function of the foundation settlement, rendering the CPRF a complex soil–structure interaction issue. Despite the recent development of computational resources and advances in numerical expertise, a detailed three-dimensional (3-D) numerical analysis, accounting for soil nonlinearities, nonlinear behavior of the interfaces between the soil, piles, and raft under various combinations of loadings remains impractical. The objective of this paper is to provide a rather simplified and straightforward design methodology for pile foundations under combined loadings. To achieve this goal, previous research works on the group effect under axial and lateral loading have been evaluated and the piles–raft interaction effect has been considered. The proposed procedure is fully compatible with structural software codes and can be straightforwardly applied to the design of the structural members, as it is able to effectively solve a CPRF under the numerous combinations of loadings required by most design codes.