A critical look at constitutive models for soils

A rough count shows that there are nearly 40-50 models published in the literature. It is useful to classify the various constitutive models in different categories depending on the fundamental theories on which they are based. The mathematical theory of elasto-plasticity is well established and has been used extensively in many branches of engineering. The framework of this theory has been a fertile ground for the development of soil models. Various permutations and combinations of yield functions, flow rules and hardening rules give rise to different models and with judicious choice, the theory has considerable flexibility to enable modelling the complex behaviour of soils in both monotonic and cyclic loading. The description of a model, therefore, from the standpoint of the solution of boundary value problems is incomplete unless the model also defines the constitutive relationships in the overconsolidated region as well.