Theoretical research and its engineering practice on critical backfill ratio in backfill mining

Good control on the backfill body’s compression ratio (BBCR) in backfilling mining technology is the key factor for guaranteeing the successful implementation of accurate control on strata movement and surface subsidence. In this paper,the multiple definitions of critical backfill body’s compression ratio (CBBCR) were given on the basis of strata movement and its control characteristics in solid-backfill coal mining,specifically including the CBBCR for the key stratum damage,the CBBCR for bending and sinking of the key stratum,the CBBCR for the bending and sinking of main roof,and the CBBCR for the overall bending and sinking. By using the roofs with periodic weighting as an exam- ple,a mechanical model for solving these CBBCRs with layer-by-layer breaking of different overlying rocks was estab- lished to analyze the relationship between layer-by-layer breaking and the corresponding tensile strength of the stra- tum,and solve the CBBCRs of the layer-by-layer breaking of the overlaying rocks. It was shown in the engineering practice at Zhaizhen Mine that the calculated CBBCR of the overall bending and sinking of the overlaying strata at 7203W backfill working face was 92. 0% ,while the actual control value was 92. 5% . All the overlying strata were not broken and controlled at the critical state of overall bending and sinking. Thus,the in-site measurement corresponded with the theoretical results. These results are expected to provide a theoretical direction for both qualitative and quanti- tative studies of the engineering design of implementing solid-backfill coal mining technology under different structures of overlaying rocks.