Formulation and implementation of an elastoplastic constitutive model for sand-fines mixtures

Sand-fines mixtures are commonly used engineered materials, and their mechanical behavior is significantly affected by density, confining pressure, as well as fines content. Although many laboratory tests have been performed on sand-fines mixtures, few works have been conducted on its constitutive law. To adequately describe the mechanical behavior of sand with different fines content, a novel elastoplastic constitutive model was developed for sand-fines mixtures by incorporating an equivalent granular state parameter into Rowe's stress-dilatancy equation, plastic modulus, and in conjunction with the correlation between the critical state and fines content. Subsequently, the Runge-Kutta schemes with automatic error control are adopted for the proposed model and implemented in a finite element code. The performance of the fines-state-dependent model with the Runge-Kutta schemes, in terms of accuracy, efficiency and convergence, is verified by analyzing element scale tests and boundary value problems. The comparisons of simulated and experimental results demonstrate that the fines-state-dependent model can effectively capture the strain hardening (or softening) and contraction (or dilatancy) behaviors of sand-fines mixtures under drained conditions. In addition, the key features under undrained conditions, such as flow, limited flow, and non-flow behaviors can also be reasonably reproduced.