Abstract

We performed series of numerical vertical compression tests on assemblies of 2D granular material using a Discrete Element code and studied the results in regard to the grain shape. The samples consist of 5000 grains made either of 3 overlapping discs (clump - grain with concavities) or of six-edged polygons (convex grain). These two types of grains have a similar external envelope, ruled with a geometrical parameter α. In the paper the applied numerical procedure is briefly described followed by the description of the granular model used. Observations and mechanical analysis of dense and loose granular assemblies under isotropic loading are made. The mechanical response of our numerical granular samples is studied in the framework of the classical vertical compression test with constant lateral stress (biaxial test). The macroscopic responses of dense and loose samples with various grain shapes comparison show that the shear resistance of a sample made of clumps increase with the grains concavity. Dense samples made of polygons are less dependant on the particle shape. This observation is not valid for loose samples made of polygons. The micromechanical origins of these results are explored by contact analysis, focusing especially on dense samples made of clumps: grain concavity furthers particles imbrications and increase shear resistance. Finally we present some remarks concerning the kinematics of the deformed samples. Whereas polygon samples submitted to a vertical compression present large damage zones (whatever polygons shape), dense samples made of clumps always exhibit thin reflecting shear zones caused by clump imbrications only, even if our granular model is cohesionless

Authors (3)