In order to investigate the influence of the defective piles with stem enlargement on the working behavior of pile foundations under vertical loadings

a numerical model was set up for the analysis of group piled foundations. A series of contrastive analyses were made to a group piled foundation including a pile with defect of stem enlargement in a shallow or a deeper depth and a pile foundation with normal piles with a three dimensional nonlinear finite-infinite element method. The basic working behavior of the pile foundation with a defective pile of stem enlargement was initially revealed by the results of the analyses; and the basic rules of the affects of pile stem enlargement defects on the distribution of axial forces among piles and the bending moments in pile caps were obtained. The results of this research are not only helpful for the understanding and rational judgment of the working mechanism

but also of practical important significance in the assessment of the bearing behavior of pile foundations including defective piles with stem enlargements and in the structural designs of piles and pile caps.