Helical Piles Installed in Cohesionless Soil by Displacement Method

Abstract

This paper presents a detailed investigation carried out for a helical pile installed in cohesionless soil by the displacement method. Laboratory experiments were conducted on models to study the various factors influencing the axial capacities of helical piles. The investigation showed that relative density of soil plays a significant role in the response of axial capacity of piles to geometrical variations in helical blade diameter and shaft diameter. Presence of a helical blade and its geometry (Dh) were found to influence the axial capacity significantly. The effect of method of installation on axial capacity of helical piles was investigated, and helical piles installed by the displacement method were found to show an improvement of axial capacity on the order of 1.1–1.4 times in compression and 1.8–3.0 times in tension from experimental observations. To augment the investigation, analyses were carried out using three-dimensional finite-element software (Plaxis 3D AE) on the numerical model calibrated using the results from the experimental investigation. Cavity expansion by volumetric strain was found to capture the effect of installation of helical piles by displacement method in cohesionless soil. The results of the parametric study accommodating the effect of installation by displacement method, considering different soil densities and geometric features of helical piles, were used to propose a set of semiempirical relations for predicting axial tensile and compressive capacities. A set of reduction factors were also proposed to accommodate the difference in end-bearing response of helical piles compared to a prismatic pile of identical toe diameter.