Macro- and micro-behaviors of granular materials under different sample preparation methods and stress paths

Abstract

A series of numerical drained tests have been performed to study the macroscopic and microscopic behaviors of granular materials prepared by three different techniques (isotropic compression, tamping, and dry pluviation). The samples consist of two kinds of ellipsoids with 1170 particles. The two kinds are equal by weight. The aspect ratios (major axis length/minor axis length) of these two kinds are 1.2 and 1.5, respectively. All samples were subjected to an isotropic confining pressure of 100 kPa before loaded along 11 different stress paths. The shear strengths of these drained tests were compared with two published yield models. Good agreement was found in general. One model showed an error of less than 5% for 90% of the time. Two microscopic parameters, the unit contact normal and the contact normal force, were examined for all specimens during axial compression loading. The principal stress ratio was found to correlate better with the contact normal force than the unit contact normal. The evolution of this microscopic descriptor was further investigated for all drained tests. The result showed a unique relationship between the strength descriptor of the contact normal force and the principal stress ratio. Excellent correlations were found for the drained tests with various intermediate stresses.