Discrete element modeling of shear band in granular materials

Abstract

Numerical biaxial tests using discrete element method (DEM) were carried out to study the shear band formation in granular materials and the microstructures of the specimen at different strain levels were carefully examined. The effect of initial density and confining pressure on the characteristics of shear band were investigated. It was found that the progressive formation of the shear band was successfully captured by the DEM simulation with flexible lateral boundaries. During the shearing, several potential shear bands are formed at the peak deviatoric shear stress. With further shearing, the potential shear bands enlarge and softening behavior happens. Finally, a persistent shear band forms and other potential shear bands deteriorate. Generally, loose state and high confining pressure “delay” the onset of shear banding. The simulation also showed that the shear band thickness decreases with increasing confining pressure and density. Meanwhile, the inclination angle of shear band in dense specimen is generally higher than that in loose specimen. The void ratio of shear band is significantly larger than other parts of the specimen. At microscopic level, the overall coordination number of the specimen decreases significantly. The coordination number in the shear band is significantly lower than that outside the shear band, which is consistent with the large porosity in the shear band. The formation of shear band is due to the bulking of lateral confining force chains and the shear band is characterized by large void ratio, low coordination number, and high particle sliding and rotation compared with other part of the specimen.