A generalised Modified Cam clay model for clay and sand incorporating kinematic hardening and bounding surface plasticity

This paper proposes a simple non-associated Modified Cam clay model suitable for clay and sand. The yield surface is taken to be that of Modified Cam clay, which is a simple ellipse. The modified model reduces the amount of shear strain predicted, and for clay requires no new parameters because the flow rule uses a well established empirical result. For sand, the critical state frictional dissipation constant is required in addition to the stress ratio at the peak of the yield surface. This permits realistic modelling of the undrained behaviour of sand in states looser and denser than critical. The model resembles more sophisticated models with yield surfaces of more complex shapes, but is much simpler. More realistic behaviour could be obtained by assuming a yield surface with the same form as the potential if required. The model is suitable for incorporating kinematic hardening for the modelling of cyclic loading of clay. In addition, bounding surface plasticity can be included to distinguish between compacted and overconsolidated sand. The contribution in this paper is therefore to provide a generalised simple model based on Modified Cam clay.The authors are grateful to Mr C.D. Khong for discussions on the bounding surface formulation of the CASM model.