Breakage behavior of sand under true triaxial stress based on discrete element method

A series of triaxial compression tests and true triaxial tests based on discrete element method are conducted numerically to investigate the particle breakage behavior of granular materials under triaxial stress conditions. The numerical investigation mainly focuses on the stress-strain behavior, the evolution of the particle-size distribution and relative breakage of the crushable granular assembly. As the confining pressure increases, it is found that the dilatancy and strain softening of granular assembly decrease, which is related to the increase in the particle breakage. Beyond a higher confining pressure, the volumetric dilatation starts to increase, caused by the increase of the particle breakage during consolidation. In true triaxial tests, the peak stress ratio decreases with the increasing intermediate principal stress ratio b. And the increase of b results in the decrease of dilatancy, which stems from the distinct increasing compaction caused by breakage with the increasing b. The internal friction angle φ decreases with the increasing confining pressure, which conforms to a logarithmic relationship, and φ increases first and then decreases with the increasing b, which conforms to the Lade-Duncan failure model. In addition, the increment of the increasing relative breakage declines with the increasing confining pressure and axial strain, which implies the existence of the optimum distribution of granular assembly. The relationship between the particle breakage and the total input energy during tests is found to conform to a unique hyperbolic correlation.