Single surface hardening plasticity model for soft clays. Mathematical formulation and implicit numerical integration

The mechanical behaviour of soft natural clays is strongly affected by mechanical degradation processes which overlap the response shown by the corresponding reconstituted material. This is interpreted as an indication of the need of more complex hypothesis on the hardening of these soils then what typically done in the Cam-Clay family models, developed with reference to the reconstituted behaviour. In the first part of this paper a single surface constitutive model is presented, the main features of which are the capability of reproducing the dependency of the elastic stiffness on the current stress state by means of a hyperelastic formulation and the ability of simulating the plastic strain driven structure degradation processes by an appropriate isotropic hardening law. This is followed by the description of a return mapping algorithm which allows the model to be implemented in finite element codes, ensuring numerical stability and accuracy requirements to be satisfied. In the final part of the paper, the numerical simulation of single element tests are illustrated and discussed.