Effective control and performance measurement of solid waste backfill in coal mining

As an effective method of disposing of mining wastes, solid waste backfill mining not only permits longwall coal mining under sensitive surface structures such as buildings and roads, but also solves environmental problems caused by mining activities. This paper proposes ultimate control indices for the backfilling effect with regard to performance requirements under different conditions such as mining below buildings, water bodies or hard strata, with regard to surface deformation, height of the water-flow fractured zone and the pressure at the workface. It is found that mining height is the key factor influencing these indices. Based on equivalent mining height theory, the backfilling ratio is proposed as a theoretical control index of the backfilling effect. This is converted to the ratio of backfilled mass to mined mass (RBM) as a direct control index that is more convenient for field monitoring. A quantitative relationship between these two indices is established and a process for controlling the backfilling effect in solid waste backfill mining is established. Specific measurements for controlling the backfilling performance are given in terms of four parameters: workface layout, backfilling material, equipment and technical process. Field results obtained in the Wugou coal mine show that the RBM is a simple and reliable direct control index of the backfilling effect.