Constitutive Modeling of Coarse-Grained Materials Incorporating the Effect of Particle Breakage on Critical State Behavior in a Framework of Generalized Plasticity

Coarse-grained materials (CGMs), including gravel, ballast, and rockfill material, exhibit a complicated stress-strain-volume change behavior, which is state dependent and influenced by considerable particle breakage even under relatively low pressure. A generalized plasticity model with a multiaxial formulation is developed for CGMs based on the critical state concept. The effect of particle breakage on their critical state behavior, including the nonlinear variation of both shear strength and void ratio with the mean effective stress, is fully incorporated with an implicit form in the current model. Two state functions and the corresponding virtual stress ratios are proposed to construct the new formulation of dilatancy, plastic flow, loading direction, and plastic modulus in the present model. The numerical analyses are performed for a series of true triaxial tests on CGMs, and model predictions are in good agreement with experimental results of true triaxial tests over a wide range of pressures. In summary, the proposed model is capable of accurately characterizing the highly nonlinear shear behavior due to particle breakage of CGMs, particularly including their strain softening/hardening and plastic dilation/contraction in various load paths.