Critical states and soil modelling

Critical states play a central role in many constitutive models. Traditionally critical states have been defined as asymptotic states in which shearing continues without further change in stresses or density. However, such asymptotic states may not be easily observed in practice and devices in which part or all oldie sample can be sheared to large deformations are required. Laboratory tests combined with discrete element modelling show the effects of journeys towards the critical state and show that a steady mobilised strength is reached at a modest shear strain whereas other parameters, such as grading and density are still changing slowly at very large strains. A grading state index is defined and introduced into a constitutive model to demonstrate how changing grading can affect the response of geotechnical systems.