During mudflows, geomaterials evolve in a very specific manner as, initially behaving as solids, they turn to flow as viscous fluids. The present paper proposes an original approach to simulate-within a single numerical framework-this transition between a solid-like and a fluid-like behavior. The model used is based on the association of an elasto-plastic and a viscous constitutive relation to describe both phases of the behavior. The transition between the two is assumed to correspond to a failure state, and the transition criterion considered is thus based on the general second-order work stability criterion. Because of their suitability to describe respectively soils and granular suspensions, Plasol elasto-plastic model and Bingham's viscous one have been considered. In this preliminary study, the global model is tested for two homogeneous loading paths with drained and undrained conditions. For these cases, it results that the radical transformation of the material behavior at failure is captured and both the solid-to-fluid and the fluid-to-solid transitions are consistently enabled, making possible a future application of this approach to gravitational flow modelling.