Strength Design and Quality Evaluation of Cemented Backfill in Narrow and Long Stope

In response to the optimization problem of the strength of the cemented filling material in the narrow and long mining area of the Jinchanghe Lead–Zinc Mine using the empty backfill method, this study systematically carried out the design and quality evaluation of the filling material strength requirements through a combination of theoretical analysis, numerical simulation, and field experiments. Based on the mechanical parameters of the ore rock filling body, theoretical calculations were carried out using formulas from the BGRIMM Technology Group, the Mitchell formula, and the Anqing Copper Mine experience formula. Combined with FLAC3D numerical simulation analysis, the stability of the filling body under the two‐step mining and filling sequence was determined. The critical stable uniaxial compressive strength of the one‐step narrow and long mining field cemented filling body was determined to be 2.13 MPa, and a regional strength structure design was proposed (bottom 9 m strength of 3.0 MPa and middle and upper 41 m strength of 2.13 MPa). Through in situ coring experiments underground, the conversion coefficient (0.84) between the laboratory and in situ strength of different ash–sand ratio filling bodies was revealed, and the filling ratio parameters were optimized (bottom ash–sand ratio 1:3 and middle and upper part 1:5). The research results provide theoretical basis and engineering reference for the strength optimization design and quality evaluation of filling materials in narrow and long mining areas, achieving a balance between safety and economy.