A contribution to optimum design of piled rafts

Abstract

The majority of piled raft foundations have been designed ignoring any contribution from the raft or pile cap, although it is well known that the raft plays an important role in the overall performance. In such conventional designs, the overall settlement of the foundation is likely to be very small, owing to the installation of more piles than are necessary. However, from an economical point of view, it is preferable that the foundation is designed in such a way that the average and differential settlements are limited to an acceptable level, but where the load-carrying capacity of the raft is taken into account. In this paper, a framework for a new design concept, in which piles are installed only beneath the central area of a relatively¯exible raft to minimize the differential settlement, is presented through the results of an extensive parametric study. The so-called`hybrid' approach, developed by Clancy, was used in the analyses. The study showed that piled rafts may be designed for negligible differential settlements by including a pile group over the central 16±25% (by area) of the raft, with the pile group stiffness approximately equal to that of the raft alone. The total pile capacity should be about 40±70% of the total applied load, depending on the pile group area ratio and the Poisson's ratio of the soil. The validity of the method is examined through the results of centrifuge model tests conducted by the authors.

Appraisal of nonlinear dynamic soil-structure interaction model for pile foundation supported structure: a probabilistic approach

“…Plan dimension of raft is considered as 10 m × 10 m which is discretized into 0.5 m × 0.5 m small elements based on a convergence study. A moderately rigid raft is selected in this study considering the relative stiffness of raft and soil (k rs ) as suggested by Horikoshi and Randolph (1998)…”

Pile Group Settlement Estimation: Suitability of Nonlinear Interaction Factors

“…The IFM is strictly not applicable to situations where the pile cap is in contact with the ground. However, given that the majority of piled rafts are designed ignoring any contribution from raft-soil interaction (Horikoshi and Randolph 1998), the analyses presented herein will be of interest to geotechnical designers. Moreover, a reliance on the contribution of the raft-soil resistance can lead to unconservative design in situations where the occurrence of ground surface settlement and/or scour by water current, for example, is possible.…”

Development of optimum design from static response of pile–raft interaction

“…In this section, the FE model of a circular raft is validated using centrifuge test data reported by Horikoshi and Randolph [37]. The purpose of this validation is to build confidence in the relevance and accuracy of the FEA for piled raft foundations.…”