ON THE ROLE OF MICROSTRUCTURE IN THE BEHAVIOR OF SOILS - EFFECTS OF HIGHER-ORDER GRADIENTS AND INTERNAL INERTIA

The role of microstructure in the behavior of soils is outlined by considering two typical examples: fluid flow and shear banding. In particular, the modifications resulting on Darcy's law and flow rule of soil plasticity due to the development of high strain gradients and internal inertia are discussed. This is done by resorting to ''complete balance laws'' for the internal variables. In the case of Darcy's law, the ''internal'' variable is an interaction stress between the porous solid and the interpenetrating fluid phase, which is required to obey an internal momentum balance equation. In the case of flow rule, the ''internal'' variable is the so-called back stress which is also required to obey a complete balance law containing both a rate and flux term.