Plastic instability of sand specimen in the form of strain localization has been explored in this paper with particular emphasis on the effect of loading condition. Simulations are carried out for drained true triaxial experiment with varying intermediate principal stress ratio and biaxial test configuration. A non-associative constitutive relation has been employed to represent the stress-strain response of sand. The instability analysis has been posed as a bifurcation problem from a uniform stress-strain condition and the onset of localization is identified as the acoustic tensor loses its positive definiteness. A detail analysis has been carried out to examine the influence of loading condition on the emergence of localization, i.e., onset shear strain and shear band orientation angle.

Keywords: Plastic instability, Localization, Shear band, Non-associativity & sand.