A numerical study of piled raft foundations

Abstract

This paper presents raft‐pile‐soil interaction for a vertically loaded flexible piled raft on layered subsoil using a two‐dimensional finite difference numerical tool. The subsoil is modeled as a linear elastic material and the raft is modeled as a beam structure under plane strain. In addition, the piles are simulated by a series of pile elements considering the pile/soil interface behavior. In the simulations, the required input parameters of soil, pile and interface are determined by back analyses of pile loading tests. Settlement, bending moment, both in pile and raft, as well as effects of raft flexibility for vertical uniform loading in the subsoil were examined. It is found that even though for vertical uniform loading, a relatively high bending moment may be induced in the piles due to lateral displacement of the stressed subsoil. For the case of a piled raft placed over a soft clay layer at ground surface the contact pressure at the raft‐soil interface is merely 4 ～ 6% of that developed in the unpiled raft. Nevertheless, the contact pressure may reach 15 ～ 25% of that of the unpiled raft if the piled raft is resting on a sand layer at the ground surface. This implies that the loading carried by the pile group could be reduced by almost 1/4 of the design load and it could eventually reduce the cost of pile group construction to a certain extent.