Microscopic calibration of rolling friction to mimic particle shape effects in DEM

Abstract

Much work has been done to characterize granular shape and to understand its influence on overall soil behavior. Thus, Wadell (Wadell 1932) introduced the concept of “sphericity” that quantifies how a particle differs from a sphere, in terms of surface area. Krumbein (Krumbein 1941) presents the first chart to visually estimate shape from the grain lengths ratios. There is much evidence showing that particle shape is relevant for mechanical responses of soils. Andò (Andò 2013, Andò et al. 2012) tested in triaxial conditions different sands with shape ranging from very angular to rounded. Using Digital Image Correlation, he showed that angular sands exhibited a larger shear band thickness compared to rounded sands. Rorato (Rorato et al. 2019b) demonstrated that a rounded sand (Caicos ooids) exhibits higher grains rotations compared to an angular sand (Hostun sand). In this work, we propose a new procedure for an optimal calibration of the DEM contact model parameters that is able to mimic the effect of particle shape without dramatically increase the computational time. In particular, our approach aims to (1) limit the number of free parameters requested, (2) respect the mechanical and kinematic triaxial responses of the sheared granular materials and (3) maintain low the computational time. The Particle Flow Code (PFC3D) developed by Itasca Consulting Group, Inc. (Itasca 2014) has been used in this work.