Experimental Investigation to Evaluate Impacts of Surface Asperities on the Shear Behavior of Granular Materials

Abstract Impacts of surface characteristics on the behavior of granular materials have been investigated experimentally. Manufactured granular materials produced by pelletization method are used to assess the relation of particle surface characteristics and overall behavior of granular materials. Surface characteristics of four different manufactured granular materials have been investigated using an optical microscope and image analysis techniques. A series of direct shear tests was conducted to investigate the development of particle crushing under shear stress of this manufactured granular material. A Plexiglas shear box was developed to reduce the friction at the boundaries of traditional steel shear box. Shear behavior of these granular materials was analyzed under three different confinement pressures to evaluate impact of stress level. The experimental study shows that asperities of grain surface give higher frictional behavior of the manufactured materials. However, higher confinement causes to crushing of asperities of the grains. Based on the grain size distribution of the sample obtained before and after the test, the abrasion of particle was most influenced by the confinement applied to the sample. The failure surface created by shear loading decreases the roughness of particle because this surface is much smoother than original. The observed evolution from strain hardening to softening with displacement is interpreted as being due to the change in the microstructures of grains. Strain accommodation from grain crushing to slip between adjacent grains is associated with the observed evolution of a fractal grain structure. The failure surface created by shear loading decreases the roughness of particle because this surface is much smoother than original.