A micromechanics-based methodology for evaluating the fabric of granular material

Abstract

A micromechanics approach can successfully model the stress-strain-strength relation of a granular material once the microcharacteristics of the material have been obtained. However, it is usually difficult to determine the fabric of natural granular materials, Using a stress-dependent micromechanics model, the elastic properties can become a function of the geometric and kinetic fabric. Also, the wave velocity can be related to the elastic properties, Consequently, this paper proposes a methodology for evaluating the fabric of a granular assembly from a set of measured wave velocities. The methodology contains three elements: (a) stress-dependent micromechanics elastic model, (b) an anisotropic elastic wave propagation theory and (c) an optimization procedure. It is verified by calibrating available wave velocity data of a glass bail assembly and washed mortar sand, The methodology is further applied to study the microstructural evolution of the washed mortar sand under biaxial stresses. Two aspects of fabric change can be observed: (a) concentration of contact normals in the major principal direction and (b) a residual fabric after subsequent loading/unloading.