Bifurcation Analysis in Sands under True Triaxial Conditions with Coaxial and Noncoaxial Plastic Flow Rules

Abstract

An important point of shear banding is that during the rotation of principal stress directions, out-of-axes deformation plays a significant role and leads to noncoaxiality between principal stress and principal plastic-strain-rate directions. Although many research works have dealt with the effect of noncoaxiality under plane-strain loading conditions disregarding the intermediate principal stress, here, the effect of noncoaxility on the onset of strain localization is investigated under true triaxial conditions because both noncoaxiality and intermediate principal stress are important factors in the investigation of shear-band formation. Therefore, a three-dimensional (3D) noncoaxial elastoplastic model is proposed and incorporated in the single hardening constitutive model to capture the stress-strain relationships and predict the onset of strain localization under true triaxial conditions for the studied dense sand. The numerical simulations illustrate that the bifurcation points comply well with the peak of the stress-strain curves observed experimentally in true triaxial tests. No bifurcation point is observed in the hardening regime by numerical simulations or experimental results near the triaxial compression condition.