Mechanical Behavior of Granular Materials under Continuously Varying b Values Using DEM

The influence of the intermediate stress ratio on the mechanical behavior of granular materials under generalized stress conditions is not well understood, particularly in regard to relationships between macroscale behavior and microscale response. The objective of this paper is to study the influence of the intermediate stress ratio, specified by b[=(σ2−σ3)/(σ1−σ3)], on the mechanical behavior of granular materials under generalized stress conditions, using the discrete element method (DEM). Selected b values were used to illustrate the influence of the intermediate principal stress σ2 on the major and minor principal stresses, σ1 and σ3, respectively. More-generalized stress conditions were identified by continuously varying b values. Specifically, 11 stress paths under truly triaxial conditions, following the stress-controlled method for a three-dimensional sphere, were simulated with continuously varying b values as well as constant b values. Differences in the stress–strain relationship results were studied, including the relationship among principal normal strains and principal deviatoric strains as well as the evolution of stress-increment and strain-increment vectors and the behavior of strain-increment vectors on the π plane. The DEM results were found to compare well with the experimental data qualitatively. The macro behavior and micro response data were described by the relationship between the stress ratio and the fabric structures representing contacts of all particles as well as strong contact regardless of varying b value.