Therefore, by assuming the prearranged protective coal pillars in the SBBM working face, the backfill body and (m - 1) bed rock as independent springs, and the entity coal in the right part as semi-infinite elastic foundation, the mth rock beam can be treated as a semi-infinite long beam.
The detailed engineering parameters and the mechanical parameters of various strata, as displayed in Figures 2 and 3, were substituted into the mechanical model of the SBBM working face.
Because of the specificity of arrangement in the SBBM working face and the filling of gangues in the gob, SBBM differs from long-wall mining in roof management, thereby leading to different rules and mechanisms of mine pressure and fracture development.
Apparently, the prediction value according to the formula in the Regulations deviates greatly from the measured results, suggesting that the prediction formula is no longer applicable to the calculation of the height of the water flowing fracture zone in the SBBM; in contrast, the calculated height by the established mechanical model fits well with the measured result, validating high reliability of the proposed calculation model.
According to the provisions in the Regulation, the thickness of the protective layer can be determined by considering the structural characteristics and mechanical properties of the coal rock in the SBBM working face:
The thickness of the bed rock far exceeded the allowable minimum thickness of the waterproof coal pillar, indicating that the aquifer was not affected by the mining activities in the SBBM. In addition, the gangues were filled in the gob as the backfill body, which then cooperated with the coal pillar to bear the load of the overlying strata, thereby effectively decreasing the height of the mining-induced water flowing fracture zone.
(1) This study proposed the SBBM method for the recovery of corner coal pillars, industrial square pillars, and irregular blocks beneath the aquifer and simultaneously addressed the problem of massive stacking of gangues on the earth's surface.
(2) Based on the technological characteristics of SBBM and the theory of elastic foundation beam, a mechanical model for the calculation of the height of the water flowing fracture zone in the overlying strata using SBBM was established.
Therefore, it can be concluded that the aquifer was not affected by mining activities, and simultaneously the mining upper limit of coal seam as well as the recovery ratio of coal can be enhanced in the SBBM.
Furthermore, in contrast with the caving mining method, the SBBM method used the gangues as the backfilling materials and filled them in the gob.
Caption: Figure 7: Illustration of the short-wall block backfill mining (SBBM) system.
Caption: Figure 8: Arrangement in the SBBM working face and key equipment.