Failure behavior and fracture evolution mechanism of layered backfill considering dip angles

The backfill with angles will be formed when using the backfill mining technique due to the flow and settlement of the slurry. The structure of a layered surface is loose, making it necessary to analyze its influence on the mechanical properties of backfill from macro, fine, and micro-scales. Standard specimens with four types of layered surfaces and four types of layered surface angles were prepared and tested by uniaxial compression and scanning electron microscopy. Based on the brittleness index, tensor crack hot spot, scalar stress cross, etc., the failure mechanism was investigated from the perspectives of strength, deformation, crack number, fabric anisotropy, cracking mode and microscopic morphology. The results showed that the strength and brittleness index decrease with the increases of layer parameters, and the influence of the layer angle is larger than that of the number of layers. The strain at each stage of the stress-strain curve varies regularly with the layer parameters. The simulation results are in good agreement with the experimental results. The cracks first appear at the layered surface, and then extend to all sides. The layer parameters are positively correlated with the number of total cracks, shear cracks, crack evolution rate, and the number of blocks, while the force between particles is weakened, and the direction of contact force chain and the total coordination number exhibit significant fabric anisotropy. The results indicated that shear cracks are more developed at the layered surface, and the bearing capacity of matrix between the layered surfaces is weak. The results can provide a theoretical basis for the design of the filling and mining processes in such mines.