DEM Modeling of Grain Size Effect in Brittle Granular Soils

The size-dependent strength of individual particles controls several key aspects of the constitutive response of brittle granular materials. Capturing this factor in numerical analyses is essential to accurately model the mechanical behavior of assemblies with particles of different size. In this study, a three-dimensional discrete element method (DEM) model is proposed to reproduce the size dependence of the particle strength by means of a bonded particle framework. Particle fragmentation is modeled explicitly through the disintegration of agglomerates made of bonded elementary spheres. Diametric and oedometric compression tests performed on different sands are used for the calibration and validation of the model. The size effect and variation of the particle strength evaluated in terms of stress and energy measures are interpreted via Weibull statistics. The DEM model calibrated with a set of diametric compression experiments successfully captures the particle strength variability and the size dependence of the failure and yielding strength at particle- and assembly-scale, respectively. The degree of fragmentation during the confined compression of sand and agglomerate assemblies are compared by quantifying the evolution of particle size distribution and a relative breakage index. The satisfactory agreement between experiments and numerical results suggests that the proposed DEM approach can be used to simulate the comminution of crushable granular solids, thus being particularly useful to study size reduction processes in cases where direct testing is impractical.