Helical Anchor Pullout Using a Semifluidized Bounding Surface Plasticity Model

The ultimate vertical pullout capacity of single-helix anchors in sand was explored using the coupled Eulerian–Lagrangian (CEL) technique to account for large deformation processes. A semifluidized bounding surface plasticity model was incorporated in a novel manner to improve the continuum representation of highly disturbed sand around the anchor, particularly under very low confinement. The model was shown to be necessary for reproducing the soil backflow beneath the helix and the experimentally measured load-displacement response. A series of CEL analyses was conducted to investigate the effects of helix pitch size, embedment depth, sand relative density, and helix-to-shaft ratio on the pullout behavior of single-helix anchors in sand. The pitch size was found to have little influence on the ultimate pullout capacity, consistent with available centrifuge observations. Increasing sand relative density contributes to greater capacity but changes the relative contributions of the shaft and helix. The helix resistance becomes more dominant in dense sand, whereas the shaft and helix provide nearly equal contributions in loose sand. The numerical results were used to extend an analytical solution for estimating the ultimate pullout capacity. The proposed solution provides excellent predictions across different sand densities and anchor geometries, suggesting its potential use in practical design.