Modeling anisotropic, debonding and viscous behaviors of natural soft clays

A new viscoplastic model is developed extended from overstress theory of Perzyna. A scaling function based on the experimental results of constant strain-rate oedometer tests is adopted, which allows viscoplastic strain-rate occurring wherever the stress state is inside or outside of the reference surface. The inherent and induced anisotropy is incorporated using the formulations of yield surface and its rotation of S-CLAY1. The bonds are progressively destroyed by plastic straining by incorporating the concept of an intrinsic yield surface. No additional test is needed for determining all model parameters compared to the Modified Cam Clay model, and the parameters determination is straightforward. The experimental verification is carried out with reference to the constant strain-rate and creep tests on two natural clays.