Load-Transfer Mechanism of Helical Piles Under Compressive and Impact Loading

Helical piles are currently used to support large compressive loads, which requires accurate evaluation of their bearing capacity. High strain dynamic load testing is increasingly used to determine the capacity of helical piles. However, the load-transfer mechanism of helical piles under impact loading has never been thoroughly examined. In this study, the load-transfer mechanism and the interpreted ultimate bearing capacity at 12%, 10%, 8%, and 5% of helix-diameter failure criteria of helical piles installed in cohesionless and cohesive soils under both axial static and impact dynamic loading are investigated numerically. Three-dimensional nonlinear finite element models are developed and verified against two case studies. The verified models are employed to conduct a parametric study covering a range of helical pile configurations. The results showed that the load-transfer mechanism depends on the spacing ratio and the selected failure criteria. Furthermore, the limit equilibrium method overestimates and underestimates the bearing capacity for helical piles installed in cohesionless and cohesive soils, respectively, compared with the numerically predicted values.