Numerical simulation study on the effect of delamination degree of waste rock cemented backfill on its uniaxial compression mechanical behavior

Delamination in waste-rock cemented backfill significantly weakens its load-bearing capacity and compromises underground stability. Understanding its effects on stress transfer and crack evolution under uniaxial compression is therefore critical for cemented backfill design and quality control in subsurface engineering. To investigate these effects, a particle flow model of waste-rock cemented backfill was developed to examine its mechanical behavior by combining laboratory tests with numerical simulations. The model incorporated aggregate particle size and distribution, multiple particle media, and contact interfaces to analyze crack evolution patterns, force-chain behavior, and energy variations from loading to failure at different degrees of delamination. The results show that: (1) a higher slurry mass concentration produced a more uniform aggregate distribution, reduced the degree of delamination in the backfill, and correspondingly increased the compressive strength of the backfill; (2) distinctly delaminated backfill exhibited layered failure, with cracks concentrated in the middle and lower layers, whereas non-delaminated backfill showed more uniform cracking; (3) the majority of cracks initiated at sharp aggregate corners during loading but propagated toward thinner cementitious matrix zones or nearby aggregate corners rather than along the original microcrack paths; and (4) severe aggregate delamination concentrated in the middle-lower layers, weakened the lower matrix, and generated extensive interfacial cracks that triggered rapid upward propagation into fine-aggregate zones, resulting in combined tension–shear failure and substantially reduced load-bearing capacity of the layered backfill. These findings enhance understanding of backfill behavior and provide practical guidance for mix design, placement, and reinforcement in underground backfilling applications.