Finite element modelling of helical pile installation and its influence on uplift capacity in strain softening clay

Abstract

This study investigated the effect of helical pile installation in undrained softening clay using a coupled Eulerian-Lagrangian (CEL) finite element modelling approach. A previously published strain softening soil constitutive model was used to evaluate soil disturbance. The influence of two key strain softening parameters was considered to assess installation-induced soil disturbance. The CEL-predicted remoulded soil strength field was then imported into a finite element limit analysis (FELA) to evaluate the subsequent influence on uplift capacity. The CEL results showed that helical pile installation caused a significantly disturbed zone of soil that measured approximately 1.4 helix diameters in plan and extended the full length of the pile. When the disturbed soil strength field was imported into FELA calculation, it was found that the solutions reported in previous literature had significantly overestimated the ultimate uplift capacity for softening clay. The numerical output informed the development of a new closed-form analytical approach to predict uplift capacity considering the influence of the installation process. The design method was shown to provide a high-fidelity representation of the numerical results.