Stress Redistribution Mechanisms and Subsidence Control of Fluidized Gangue Backfilling in Underground Coal Mining: Integrated Experimental and Numerical Investigation

ABSTRACT Underground coal extraction creates extensive goafs leading to overlying strata movement and surface subsidence, threatening infrastructure and mining safety. While traditional backfilling methods exist, the specific mechanisms by which fluidized gangue backfilling reduces mining‐induced subsidence remain poorly understood, limiting optimization of design parameters. This study investigates these mechanisms through integrated experimental testing and numerical simulation. Laboratory compression tests on natural caved gangue and composite specimens with varying Talbot indices (0.2–0.8) characterized load‐bearing behavior under uniaxial compression up to 20 MPa. Results reveal that grouting with fluidized backfill slurry enhances initial compression resistance by 50%–70% during early loading phases while maintaining similar ultimate load‐bearing capacity. Numerical simulations using FLAC3D examined stress redistribution and deformation patterns under different backfill thicknesses (0–3 m) and mining advance distances. The primary mechanism identified is effective load transfer through stress redistribution, where composite backfill creates alternative load pathways for redistributing overburden loads across the entire goaf area rather than concentrating forces at discrete pillar locations. Fluidized gangue backfilling with 3 m equivalent thickness reduces maximum stress concentrations by 56.8% and limits surface subsidence to 0.60 m compared to 3.50 m under traditional caving methods. The composite backfill‐pillar co‐bearing system exhibits synergistic load‐sharing effects, with optimal performance achieved when backfill equivalent modulus approaches 60%–70% of coal pillar stiffness. These findings provide quantitative guidance for optimizing fluidized gangue backfilling design, offering a practical solution for subsidence control in underground mining operations.