An updated critical state model by incorporating inertial effects for granular material in solid–fluid transition regime

Abstract: The open question of granular solid–fluid transition plays an important role in both modeling natural hazards and industrial particulate process. The well-developed critical state plasticity theory for granular solids and μ(I) theory for granular liquids are limited in terms of solving this problem. Therefore, as a first study, an updated critical state model was mathematically formulated and proposed for granular material in the solid–fluid regime for its friction and dilatancy behavior. The proposed model is consistent with classical critical state plasticity theory for granular solids and μ(I) theory for granular liquids. The introduction of two indices in the updated critical state model extends the validity domain in modeling friction and dilatancy behavior in granular materials. The updated critical state model successfully predicted the critical states in q-p-I space and ϕ_s-p-I space from 96 discrete element method (DEM) simulations of triaxial loading cases with different initial porosities and confining stresses at various loading rates from slow to fast where the inertial number is from 10^–4 to 0.2. The proposed critical state theory is believed to provide a new approach toward developing a visco-elasto-plastic framework for granular material in solid–fluid transition regime. Graphical abstract: [Figure not available: see fulltext.]