Large deformation finite element analyses of axially loaded helical piles in cohesive soil

Abstract

Large deformation finite element (LDFE) analysis is suitable for research on soil-pile interaction. The objectives of this study were to develop an LDFE model for axially loaded double-helix piles and to examine the factors that control their failure modes. The model was implemented with the re-meshing and interpolation technique with a small strain approach. Three types of helical piles in clay modeled as a Tresca material were simulated in an axisymmetric setup. The model was calibrated against the results of centrifuge model tests. Analyses show that the failure mode changed gradually from a cylindrical shear mode (CSM) to a transitional failure mode and then an individual bearing mode (IBM) with increasing inter-helix spacing. Current results suggested that there might not be a unique inter-helix spacing ratio that distinguishes CSM from IBM. Further, the effects of helix embedment depth, inter-helix spacing, and undrained soil shear strength on the failure modes were assessed by parametric analyses. Finally, the failure modes and helix-bearing factors, shown to depend on these parameters, were summarized in several charts for potential practical applications. Results suggested that the lower helix's bearing factors remained unchanged, but the upper helix's bearing factors changed with the embedment depth and failure modes.