Seismic analysis of stone column improved liquefiable ground using a plasticity model for coarse-grained soil

Abstract

This paper presents the seismic analysis of stone column (SC) improved liquefiable ground using a three-dimensional (3D) plasticity model with unified description of coarse-grained soil (CGS). The model is a modification of an existing plasticity model for large post-liquefaction deformation of sand, with improvements on the formulation for strength characteristics exhibited by CGS. According to requirements of FLAC3D User-Defined-Model (UDM), the model is implemented into the finite difference code FLAC3D, for which a method synchronizing the mapping centres and sharing necessary internal variables of subzones is developed to resolve the computational stability issue caused by the mixed discretization technique of FLAC3D. The model is validated against monotonic/cyclic and undrained/drain laboratory tests under 8 different stress paths and initial states on a gravel material and Toyoura sand. A centrifuge shaking table test on SC improved liquefiable ground is simulated adopting the model. The results show that the constitutive model and analysis method are effective in reproducing the liquefaction behaviour of CGS ground under seismic loading. Parametric analysis for liquefaction mitigation effects of SCs is further conducted, highlighting the importance of densification and maintaining drainage efficiency of SCs. Results show that the SC’s effective improvement area is approximately 2–3 times its diameter.