A Numerical Study on the Behaviour of Piled Raft Foundation

Author(s): Dr.M.Heeralal, Dr. Rakesh J. Pillai, Sona Gokuldas and Athira Gopinath
Paper category: Proceeding
Book title: International Conference on Advances in Civil Engineering and Sustainable Construction
Editor(s): T.Ch. Madhavi, G. Prabhakar, Santhosh Ram, and P.M. Rameshwaran
Print-ISBN: None
e-ISBN: 978-2-35158-161-2
Publisher: RILEM Publications SARL
Publication year: 2016
Pages: 117-125
Total Pages : 9
Language : English

Abstract: The increase in urbanization over the past few decades led to a decrease in the availability of useful land and a rapid increase in the number and height of buildings on problematic subsoil. Piled raft system proves to be more effective in such cases. In conventional piled foundation it is assumed that pile cap doesn’t take any load even if it is in contact with the soil. Therefore piles have to be longer to extend to deep harder strata. In case of raft foundation to take full load, very thick raft have to be provided which increases the cost and settlement of the structure. Hence Piled Raft Foundation (PRF) in which the load is shared by raft through contact with the soil and piles through skin friction is the best solution where shorter piles and raft of lesser thickness can be provided. PRF increases the bearing capacity by load sharing and improves serviceability by decreasing maximum, differential settlement and tilting of structures. It also decreases internal stresses and bending moment in raft by strategically arranging piles beneath the raft. They have a complex soil structure interaction. This often requires numerical methods which help validate these problems using least computational effort. Behaviour of PRF is influenced by a variety of factors such as the thickness of raft, diameter of piles, length of piles, spacing of piles, number of piles etc. These factors influence the economical, effective and safe design of PRF. Here, numerical analyses have been carried out using Geotechnical Finite Element Software Plaxis-3D to investigate the effect of above said factors on the settlement, bending moment and load sharing of PRF. The study has been conducted on a hypothetical model in soft soil. The standard raft size used was 10mx10mx1m and the pile diameter and length were 0.5m and 16m respectively. A 4x4 pile group with 1.5m spacing was considered. The foundation was acted upon by a load of 120MN. Later the behaviour of piled raft under lateral and vertical load is studied on another model. The settlement of the central pile is expressed as nominal displacement and it is plotted with pilestiffness ratio for both the loading conditions. The study shows that the length of piles, spacing and number of piles has a significant effect on thesettlement, bending moment and load sharing of piled raft.

Online publication: 2017
Publication type: full_text
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