Size Effect of Gangue Backfill Structures on Overburden Deformation and Stress Evolution in Cut-and-Fill Mining

Traditional underground backfill mining generally faces persistent bottlenecks such as insufficient filling material supply, high transportation costs and low filling efficiency. As an emerging green mining technology realizing in situ backfill material self-sufficiency, cut-and-fill mining provides an effective solution to the above problems, but the influence mechanism of its key geometric parameters on engineering performance remains unclear, restricting standardized parameter design and field promotion. Taking a shallow-buried coal mine in Ordos as the engineering background, this study carries out physical similarity simulation tests to systematically investigate the evolution laws of overburden displacement and stress distribution under three controlled scenarios: a baseline condition (4 m mining thickness, 10 m filling width), reduced mining thickness (2 m, 10 m), and increased filling width (2 m, 15 m). The results show that mining thickness acts as the dominant factor governing the strata control effect: when mining thickness is reduced from 4 m to 2 m, the maximum vertical displacement at the 10 m survey line decreases by 53.8%, the coal pillar stress concentration factor drops significantly, and the main roof maintains structural integrity without large-scale fracture. Increasing filling width enhances the bearing capacity of gangue pillars and restores filling zone stress closer to the in situ level, but tends to induce separation fractures in higher strata. Overall, the strata behavior of cut-and-fill mining presents distinct zoning characteristics, with high-position strata movement transitioning to coordinated integral deformation instead of severe separation and fracture. The findings provide an experimental basis and design reference for geometric-parameter optimization and engineering application of gangue backfill materials in underground mining.