Particle-to-Particle Interaction during Shearing of Granular Materials

The constitutive behavior and deformation characteristics of uncemented granular materials and aggregates are to a large extent derived from the fabric or geometry of the grain structure and interparticle friction resulting from normal forces acting on particles or particle groups. The shear strength of such materials is mainly attributed to the true friction, particle rearrangement/interlocking (dilatancy effects), and crushing. During shearing, particles will slide and/or roll as they interact with each other. In this paper, Computed tomography (CT) was used to acquire high-resolution 3D images of a cylindrical specimen composed of spherical plastic particles. The specimen was tested under axisymmetric triaxial loading condition. Post CT analysis included conducting a comprehensive digitization of particle coordinates at 3 sequential loading stages. Particle-to-particle interaction and visualization in 3D space is presented and discussed. Compared to particle sliding, rotation plays a major role in the shearing resistance of granular materials. The cumulative vertical rotation angles can be as high as 38° and the horizontal rotation angles have values as high as 60°.