On the isotache viscous modelling of clay behaviour using the hyperplasticity approach

The thermodynamically based hyperplasticity framework is employed to develop a hyper-viscoplastic constitutive model describing clay's creep and rate-dependent behaviour. The proposed model complies with the concept of the isotache viscosity and the paradigm of the critical state soil mechanics that is the uniqueness of the critical state friction envelope. A versatile force potential or dissipation rate function is presented that provides adjustability of the location of the critical state while securing a unique critical state friction envelope. A non-associated flow rule as an essential property of frictional material is adopted by further development of the force potential. Adequacy of the proposed constitutive model is evaluated through the simulation of the triaxial tests conducted on Hong Kong marine deposits.