Laboratory Analyses of Noncoaxiality and Anisotropy of Spherical Granular Media under True Triaxial State

Abstract

Anisotropy of the soil is responsible for its noncoaxial response. In simple shear and hollow cylindrical torsional shear tests, considerable noncoaxial responses were detected as a result of the stress-induced anisotropy caused by the rotation of the principal stress axis, while true triaxial tests on the noncoaxial and anisotropic response of perfectly spherical particles have seldom been reported. In consideration of the influence of the three principal stress orientations, true triaxial tests were conducted on uniformly sized spherical glass balls using the stress path of fixed-axis shear with constant values of p′ and b in the deviatoric plane. Samples with inherent anisotropy were prepared to study the evolution of noncoaxiality and anisotropy as a result of the loading process across the entire deviatoric plane. Test results indicate that the glass bead samples exhibit minor deformation and strength anisotropy in various sections of the deviatoric plane. The noncoaxial behaviors exhibit apparent orientation-dependent and b-dependent properties. This study would provide a valuable reference for granular materials with different shapes and gradations in nature that are subjected to true triaxial stress conditions.