Constitutive cladistics: the progeny of critical state soil mechanics

Discussion of the historical context of the development of the Cam clay model is used as a vehicle for description of the characteristics required for membership of the family of critical state models and of the genus of Cam clay models. It is shown that quite different routes to generation of constitutive models can produce essentially equivalent results. The lasting significance and extensive penetration of the framework of Critical State Soil Mechanics is emphasised.