Triggering of static liquefaction behaviour of undrained granular materials: A DEM study

Loose sandy soil subjected to undrained shearing manifests deviatoric strain softening and such a behaviour has been referred to as static liquefaction. The triggering of static liquefaction corresponds to effective stress ratio, referred to as instability ratio, ɳɪS. The ɳɪS for isotopically consolidated specimen exhibits a unique relation with the state parameter, Ψ which has significant potential in estimating liquefaction risk both static and cyclic liquefaction (instability type). However, most natural soils are anisotropically, K ≠ 1 consolidated (most like Kₒ) and ɳɪS-Ψ relation for K = 1 consolidation is not directly transferable. This study presents discrete element method (DEM) simulations for undrained tri-axial condition for K = 1 and Kₒ consolidated specimen which exhibited distinctly different ɳɪS-Ψ relation. The fabric anisotropy (and invariant of deviatoric stress and fabric tensors) was found to be the key factor that changes those relations. The fabric anisotropy has to be considered in constitutive relation for modelling such behaviour.