An elastoplastic-viscoplastic soil model for cyclic loading

Abstract

A mobile projection centre extension to an existing elastoplastic-viscoplastic soil model is presented in this work. In this formulation, the projection centre evolves according to the stress path experienced by the soil, approaching it during the loading process. In this way, the elastic (within which the behaviour is elastic) and the viscous (within which the behaviour is non-viscous) nuclei, will move with the projection centre. These nuclei may have reduced dimensions and reproduce more realistically the inelastic and time dependent soil response under a larger set of stress paths. The proposed formulation is based on the continuous plasticity model with a viscous mechanism proposed by Kaliakin and Dafalias. The observed occurrence of creep deformation in stiff clays at small levels of deviatoric stress was one of the motivations for this work. It is important to note that the majority of numerical and laboratory studies of the effect of strain rate on the behaviour of soils usually refers to normally consolidated soils, and, as already reported by Hashiguchi and Okayasu, further theoretical and experimental studies on the time dependent behaviour of overconsolidated soils are needed.