Influence of particle shape on the frictional strength of sediments — A numerical case study

Numerous direct and ring shear tests supply that composition and texture of sediments are crucial for shear and frictional strength. We simulate particle interactions on a micro-scale level during shearing with a numerical shear box using the Discrete Element Method (DEM). Based on the granular model approach detailed information about slip localisation and rates, forces at particle contacts, as well as particle rotation can be quantified as function of particle shape, stress conditions, and shear rate. Our numerical experiments show that the deformation behaviour of ‘clay’ is largely controlled by their particle shape. Two key factors, sphericity and roughness, could be identified as relevant for frictional strength, shear zone development, and particle rotation with sphericity dominating over roughness.Decreasing sphericity leads to complex initial microfabrics whose breakdown with increasing strain is caused by particle rotation. Preferred particle orientation favours low friction, decreasing volume strain, and the evolution of particle domains of similar orientation. Decreasing roughness results in particle interlocking of different degrees which obstructs slip and rotation to preferred orientations so that friction is high and volume strain positive.Spatial and temporal shear zone development depends on the roughness of particles. Increasing roughness precludes shear zone development and particle domain evolution. Shear zone localisation depends on particle sphericity. Increasing sphericity leads to more localised but vertically dilated deformation.