Numerical Modeling Load Displacement Behavior of Screw Piles under Seismic Loading in Soft Soil

Abstract

Steel screw piles are deep foundations made of a square or circular shaft with one or more screw-bearing plates. This study focused on numerical modeling of pullout behavior of screw piles installed in layered soil and subjected to seismic loading. Six models of screw piles (HPT1, HPT2, HPT3, HPT4, and SPT2) were analyzed numerically using PLAXIS 3D software. All screw piles were subjected to a static uplift load, but the screw piles (HPT1 and HPT3) are subjected to additional seismic loading. The seismic loading represents the range of peak ground acceleration (0.25g and 0.47g) of earthquakes that hit Baghdad city in the last few years. The pullout failure load was assumed corresponding to a displacement of around 5% of the helix diameter obtained from numerical analysis, which gives quite similar values to those recorded experimentally. Individual plate bearing was the failure pattern for a screw pile with a spacing to diameter ratio of (S/D=3), while cylindrical shear failure was the failure pattern for a screw pile with (S/D=2). The numerical simulations revealed that the number of helices has a substantial impact on the axial displacement and failure pullout capacities of the screw pile when subjected to seismic loading. While the number of screw-bearing plates has a very slight effect on the lateral displacement.