Non-linear finite element analysis of piled-raft foundations

This paper presents the results of three-dimensional non-linear finite element analysis of raft and piled raft foundations that have been loaded until failure. The raft, pile and soil have been discretised as eight-noded brick elements. The soil has been modelled as a Drucker-Prager elasto-plastic medium. The analyses have been done for a raft, a piled raft, a group of piles and an individual pile. The load-settlement behaviour of all these foundations is presented. The effect of raft thickness and soil modulus on the load-settlement behaviour of rafts and piled rafts is also presented. The axial load distribution for piles in a piled raft foundation is shown, the development of contact stress with increase in loading intensity is presented for rafts, and curves of contact stress against settlement are shown for rafts and piled rafts. The addition of even a small number of piles has been found to increase the load-carrying capacity of a raft foundation. The axial load distribution shows that the piles in a piled raft foundation reach their ultimate capacity earlier than the raft does. The contact stress is found to be minimum at the centre of the raft and maximum at the corner. When the raft reaches its ultimate load-carrying capacity, uniform contact stress is found below the raft except for a very small zone at the corner of the raft. This uniform contact stress is found to be the maximum value that can develop below a raft and a piled raft. The finite element results compare well with the reported literature.