Effect of non-coaxial plasticity on onset strain localization in soils under 3D stress condition

The non-coaxality of constitutive relationship has strongly influenced the predictions of the inception of strain localization for soils. It was shown that since the classical non-coaxial theory was built only on the basis of 2D coaxial stress space, here a 3D non-coaxial constitutive framework was proposed based on 3D coaxial stress space and employed for predicting the onset of strain localization in soils. Comparisons between numerical predictions and experimental data were also provided. The analytical results showed that a non-coaxial plastic flow theory needed to be incorporated in the classical constitutive model to describe the bifurcation, which would lead to a correct prediction of the state of bifurcation. It was also concluded that because of considering the influence of the third stress invariant on the non-coaxality, the bifurcation analysis based on 3D model would get more precise results than that based on 2D model under plane strain conditions.