The Effect of Raft Size and Pile Length on Load-Settlement Behaviour of Axisymmetric Piled Raft Foundation


D. K. Maharaj

Birla Institute of Technology and Science, Pilani, Rajasthan, India
Assistant Professor, Civil Engineering Group, BITS, Pilani, Rajasthan, India


Birla Institute of Technology and Science, Pilani, Rajasthan, India
Lecturer, Civil Engineering Group, BITS, Pilani, Rajasthan-333031, India


Nonlinear finite element analyses have been done to see the effect of raft size and pile length on the load settlement behaviour of axisymmetric piled raft foundation. Analyses have been done by NLAXIFEM-Nonlinear axisymmetric finite element software. The piles in the piled raft foundation have been represented as an equivalent annulus of same volume. The raft, pile and soil have been discretized into four noded isoparametric finite elements. The soil has been modeled as Von Mises elastoplastic medium. The load carrying capacity of raft foundation is found to increase with increase in size of the raft. This increase is not proportional to the increase in size of the raft. The effect of pile of length even equal to the diameter of the raft is found to reduce settlement of raft foundation significantly and also to increase load carrying capacity. Such piles of smaller length can be used successfully as settlement reducing piles in a piled raft foundation. The range of settlement reduction varies from 0 to about 50 percent. For the same size of raft and length of pile , with proportional increase of the two has been found to increase the initial overlap of the two load settlement curves. The effect of increase in length of pile is to increase the load carrying capacity of piled raft foundation. For the same length of piles below raft, the improvement is more for smaller raft than that of the larger raft.

Keywords: Piled raft foundation, raft, settlement, load carrying capacity, pile


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