Particle Size Effect on the Evolution of Stress and Fabric in Granular Materials under True Triaxial Conditions

Particle size significantly influences the macroscopic and microscopic responses of granular materials. The main purpose of previous works was to investigate the macroscopic response, but the influence of particle size on the evolution of microstructures is often ignored. The particle size effect becomes more complex under true triaxial stress conditions. Using the discrete-element method, a series of true triaxial numerical tests were carried out in this study to investigate the particle size effect. The mechanism of the particle size effect was elucidated from the perspective of similarity theory first. Then, the evolution of the stress and fabric for the whole, strong, and weak contact network was investigated. Meanwhile, the role played by strong and weak contacts in the particle size effect was discussed. The numerical results demonstrate that the peak stress ratio of the granular materials is enhanced as the particle size increases, which is caused by strong contacts. The peak stress ratio shows a linear relationship with particle size. The particle size effect on the strength is greater under the triaxial compression condition than under the triaxial extension condition. The proportion of sliding contacts within weak contacts gradually increases as the particle size increases. At nonaxisymmetric stress conditions, stress and fabric display noncoaxial behavior on the π-plane, and an increase in particle size enhances the noncoaxiality, which mainly originates from the weak contacts.