Theoretical research on mass ratio in solid backfill coal mining

The mass ratio is defined to describe the quantity ratio of solid materials backfilled into the stope and raw coal mined out when using solid backfill coal mining technology (SBCMT), and it is a direct control index guaranteeing the backfilling effect in this technology. Design of the backfill body’s compression ratio (BBCR) relies on goal of backfilling coal mining and corresponding equations, while BBCR is strictly controlled by mass ratio. Based on the mechanism that backfilling body controls the movement of overlying strata, the paper establishes the relation equation of mass ratio and BBCR. As for solid material directly affect the design value of mass ratio in SBCMT, tamping arm’s tamping force is the base of implementing index control on mass ratio and backfilling process is the approach of implementing index control on mass ratio, further study on functional relationships between mass ratio and key parameters of backfilling process shows that, with fixed solid backfill material and tamping force, more times of tamping, smaller natural repose angle and higher pile height contribute to a bigger mass ratio. On this basis, this paper establishes the method and design flow of mass ratio and proposes engineering control measures at last. The actual measurement of mass ratio at backfill working face in Zhaizhen Coal Mine shows that, when the solid backfill material is selected as gangues and tamping force is designed as 2 MPa, then the number of tamping times is 5–8, tamping angle is 5°–35°, natural repose angle is 35° and the pile height is 1.8–2.2 m, the mass ratio is controlled to the average value of 1.25, which is higher than designed value of 1.15; furthermore, a bigger mass ratio contributes to better BBCR control and backfilling effect.