Finite element modelling of pile penetration in sand considering the effect of fabric anisotropy

Pile penetration in sand is strongly affected by initial soil fabric and fabric evolution, but these effects are often neglected in conventional numerical analyses. In this study, an explicit Lagrangian finite element framework was developed in Abaqus/Explicit to simulate large-deformation pile penetration in Fontainebleau sand. An anisotropic critical state sand model was implemented through a VUMAT subroutine to capture the evolution of sand fabric and anisotropic behaviour during penetration. The numerical results were first validated against centrifuge test data and then used to investigate the effects of relative density, bedding plane orientation, and non-coaxial strain increment on pile resistance. The results show that the anisotropic model provides better agreement with the experimental data than the isotropic model, while the isotropic model overestimates pile resistance. The anisotropic model shows volume contraction near the pile shaft in loose sand and localised volume expansion in dense sand. The initial bedding plane orientation significantly affects pile resistance, with the resistance trend varying with penetration depth due to fabric rotation and the evolution of anisotropy variables. In addition, neglecting non-coaxial behaviour produces only a slight local increase in pile resistance at greater penetration depths. These findings highlight the importance of incorporating sand fabric anisotropy in numerical simulations of pile penetration in sand.