Constitutive modelling of non-cohesive soils under high-strain rates: a consistency approach

Abstract

Rapid loading of sands is a common issue in geotechnical engineering problems such as projectile or free-fall impact. At high strain rates (HSR), soils show more strength and enhanced dilation (viscoplastic behaviour) compared to the response at low rates (inviscid behaviour). However, few constitutive models account for the viscoplasticity of sands. Hence, the development of viscoplastic models is highly desired. Usually, viscoplasticity is modelled using overstress methods. However, overstress methods impose an overall modification of the constitutive equations, which prevents control of the evolution of internal state variables and the enforcement of the consistency condition. In this study, a generalised consistency-viscoplasticity method is proposed and applied to a non-associative modified Mohr-Coulomb model with coupled stress-dilation relation. The influence of strain rate is incorporated using a work-energy approach by way of an inertial coefficient. Two explicit integration strategies are proposed and compared, and guidelines for their implementation are shared. The numerical response of the model is tested by using drained triaxial simulations under constant axial strain rate, relaxation and impact loading. The results indicate that the consistency-viscoplasticity is a feasible alternative to simulate soil behaviour under HSR, capturing reasonably well the observed experimental responses.