Key Parameter Optimization for Longwall Paste Backfill Based on Time-Dependent Backfill Strength

Paste backfill strength exhibits obvious time-dependent growth, which directly determines the supporting effect and parameter design in longwall backfilling mining. To optimize key parameters for roof stability and surface protection, this study carried out laboratory tests, numerical simulations, and field validation on the E1302-B working face in Gaohe Coal Mine. Results show that the strength of paste backfill increases logarithmically with curing age. The optimal backfilling step distance is 2.4 m, the recommended final cured strength is 4.01 MPa with significant marginal effects, and the backfilling ratio should be no less than 92% to meet Grade-I surface protection requirements. Field applications demonstrate that under these parameters, roof deformation is controllable without fracture, and all surface deformation indexes are within 50% of the standard limits. This work provides a reliable method and practical guidance for parameter optimization in longwall paste backfilling mining.