Natural disasters like landslide, mudflow and debris flow often cause catastrophic failures in civil
infrastructure and may give rise to high rates of strain (102-104/sec) in soil. Rate of induced strain (or
stress) plays a significant effect on the strength and stiffness of soil. In this paper, we investigate the
high strain-rate behavior of sand by developing a rate-dependent, multi-axial, viscoplastic two-surface
constitutive model. The model is based on the concepts of critical-state soil mechanics. Perzyna’s
overstress theory is incorporated in this model to reproduce viscoplastic behavior of sand under high
loading rate. Nonassociated flow rule is considered. The rate-dependent model parameters are determined from experimental data of split Hopkinson pressure bar test under high rate loading.
Model performance is demonstrated for different sands.