MICROSCOPIC DEFORMATION MECHANISM OF GRANULAR MATERIAL IN SIMPLE SHEAR

Abstract

The deformation of granular material was simulated by an assembly of cylinders (made of photoelastic material) packed at random in a two-dimensional simple shear apparatus. From the detailesd observations on the change of granular fabric due to shear, and from the analyses of interparticle contact force among grains, we obtained some experimental facts which must be taken into account in proposing a granular model of sand.With the increase of shear stress in the simple shear test and direct shear test, the normals N_i to the contact planes tend to concentrate toward the maximum principal stress axis. This tendency of the concentration of N_i is not determined by the magnitude of applied shear displacement but by the intensity of mobilized stress ratio τ/σ_N. The preferred direction of N_i gradually rotates with the rotation of principal stress axes during shear deformation. The sliding in microscopic scale at contact is, at any one instant, confined at some preferred contacts. According to the microscopic study of granular fabric of sand deformed in the direct shear apparatus, the similar characters are also observed.