A numerical study of macro-mesoscopic mechanical properties of gangue backfill under biaxial compression

Based on the Particle Flow Code (PFC2D) program, we set up gangue backfill models with different gangue contents and bond strength, and studied the stress–strain behaviours, the pattern of shear band and force chains, motion and fragmentation of particles under biaxial compression. The results show that when the bond strength or contents of gangue are high, the peak strength is high and the phenomena of post-peak softening and fluctuation are obvious. When gangue contents are low, the shape of the shear band is symmetrical and most strong force chains transfer in soil particles. With an increase in gangue content, the shape of the shear band becomes irregular and the majority of strong force chains turn to transfer in gangue particles gradually, most of which distribute along the axial direction. When the gangue content is higher than 50%, the interconnectivity of strong force chains decreases gradually; at the same time, the strong force chains become tilted and the stability of the system tends to decrease. With an increase in external loading, the coordination numbers of the system increase at first and then decrease and the main pattern of force chains changes into columnar from annular. However, after the forming of the advantageous shear band, the force chains external to the shear band maintain their columnar shape while the inner ones bend obviously. As a result, annular force chains form.