Validation and applicability analysis of a novel soft-shell contact model for coated granular materials: discrete element modelling and experimental study

Abstract

Natural granular materials are commonly multiphase, with a typical state being the combination of relatively rigid internal particles and an externally degraded or soft shell. Engineered granular mixtures are frequently in the state with soft shell, such as polymer-reinforced ballast, asphalt mixture, and methane hydrate sediments, etc. For a long time, soft-shell particles are treated as equivalent homogenized particles in both analytical and DEM simulation. Given this, a novel contact model was recently developed to refine the contact relationship of soft-coated spherical particles. In this work, the Soft-Shell (SS) contact model is embedded in EDEM via the API module to obtain the triaxial shear behavior of soft-coated spherical particles. Then experimental triaxial tests with silicone-coated steel balls are conducted to validate the SS contact model. It is shown that DEM modelling with the SS contact model closely matches the experimental results in both macroscopic strength and deformation before peak stress, whereas the contact model with modulus homogenization consistently yielded excessive volumetric contraction, deviating from the experimental observations. Since the shell-to-core thickness ratio and modulus ratio are two key parameters of soft-coated particles, the applicability parameter ranges were suggested when using the SS contact model.