Impact of backfill mining on mining subsidence under repeated mining conditions

Taking a coal mine in Shanxi Province as the engineering background, this study establishes a refined three-dimensional numerical model with a size of 900 m × 360 m using MIDAS GTS NX based on field geological data. Adopting the Mohr–Coulomb constitutive model, reasonable boundary conditions and only self-weight stress for calculation, the model is employed to analyse the characteristics of surface movement and overburden stress under single-seam and repeated mining conditions with and without gangue backfill in the No. 13 coal seam. Numerical results demonstrate that lower-seam backfill can restrain surface subsidence and along-strike horizontal deformation under repeated mining, yet its subsidence-control performance is inferior to that in single-seam mining; the preformed mining stress arch from upper coal extraction weakens subsidence reduction efficiency of backfill but strengthens its restraint on lower roof deformation. The research conclusions offer practical guidance for backfill scheme optimisation and mining subsidence control of multi-seam repeated mining in analogous coalfields.