A viscoplastic recoverable sensitivity model for fine-grained soils

Full-flow penetrometer testing in fine-grained soils indicates that undrained shear strength decreases due to remoulding induced generation of excess pore pressures and increases due to strain rate effects and dissipation of excess pore pressures. This paper presents a viscoplastic strain-softening-hardening constitutive model that captures this duality of behaviour via non-local regularisation, strain rate dependency, and consolidation induced recovery of sensitivity. The model is based on Structured Modified Cam Clay and Perzyna's overstress framework. Validation of the implementation is first demonstrated through simulation of constant rate of strain triaxial and oedometer compression tests performed on different clays. The model is then applied in large deformation finite element analyses of monotonic and variable rate T-bar penetration to demonstrate successful numerical implementation and its ability to simulate strain rate effects. Finally, the model is applied in the simulation of undrained cycles of penetration of a T-bar penetrometer in kaolin clay and a carbonate silt and compared with data from geotechnical centrifuge experiments. The results show that the model without sensitivity recovery significantly underestimates the consolidated-undrained resistance in both soils, suggesting that recoverable sensitivity is an aspect of behaviour that ought to be considered in the development of constitutive models for soft sensitive soils.