A viscoplastic constitutive model for unsaturated geomaterials

In this paper a viscoplastic constitutive model for unsaturated geomaterials is presented. The constitutive laws for the description of the time-dependent mechanical behaviour of saturated and unsaturated geomaterials generalise the isotach approach proposed by Å uklje [52] to the elastoplastic strain hardening based constitutive laws for unsaturated soils. The formulation encompasses strain rate effects and allows the description of the coupled effect of strain rate and suction on the viscoplastic behaviour of geomaterials. The model has been used to simulate tests involving variable stress and/or strain rate conditions, including creep phases and soaking tests. Numerical results demonstrate its reliability in reproducing the general features of the rate-dependent behaviour together with the dependency upon suction. Further tests are currently under consideration to extend model verification to others saturated and unsaturated geomaterials.