Three-dimensional analysis of pile groups subject to torsion

Abstract

A series of three-dimensional finite-element models was developed to investigate the non-linear behaviour of pile groups connected to rigid caps and subjected to torsion. Pile groups of sizes 1 × 2, 2 × 2 and 3 × 3 installed in sand were analysed to investigate group resistance as well as the variation of pile flexural and torsion deformation. Furthermore, the relative contributions of the pile cap, pile torsion resistance and pile lateral resistance to group torsion resistance were quantitatively evaluated. The influence of group size, pile spacing, pile length, cap condition and soil stiffness was thoroughly explored. Piles were assumed to behave in a linear elastic fashion, while soil was modelled by way of the non-linear hardening-soil model. The numerical results showed that the contribution of the torsion strength of individual piles to the group overall strength decreases with the increase in group size and pile spacing but increases with the increase in pile length and soil stiffness. Among these parameters, the torsion resisted by individual piles ranged from 20 to 45% of the external applied torque. Moreover, it is found that the pile cap contributes about 7% of group resistance for surface pile caps, while this contribution increases up to 53% for embedded pile caps.