Study On The Layout Of Drilling Holes Of Grouting Backfill Into Isolated Areas Within Overburden For Mining Under Villages On Stopping Line

Village-overlaid coal zone on stopping line refers to the coal resource that cannot be excavated due to the overlaid villages only on stopping line. The technique of grouting backfill into isolated areas within overburden, which combines the filling body and isolated coal pillar to control the bending of key strata and subsidence of surface,is a useful method for partial-backfill mining. For this kind of grouting backfill mining,the key strategy is how to select the position of the first grouting boreholes,which determine the starting grouting time and control area of grouting backfill and even the final control effect of grouting. Since the caving mining method was applied in the early mining process of the working face on stopping line,the advanced surface subsidence of village-overlaid coal zone has occurred ahead of the working face,which made the layout method of the first grouting boreholes different from complete-backfill mining. In order to find the layout method and deformation law during the mining process of the first grouting boreholes,the thesis carried out the research by comprehensive use of theoretical analysis,physical simulation and field measurement.Theoretical research has suggested that for grouting backfill on stopping line,the main principle of the layout of the first grouting boreholes is that the primary key stratum block which is next to the village-overlaid coal zone should be protected from being rotated by the posterior broken block after the first grouting boreholes produce the effect of backfilling, thus ensuring the overburden stability of village-overlaid coal zone,controlling the surface subsidence effectively and protecting the village.Analogous simulation experiment showed that changes in the distance of the first grouting boreholes and stopping line respectively from village-overlaid coal boundary have different influence on surface subsidence. When the first grouting boreholes are arranged on the boundary of village-overlaid coal zone or inside,the village zone would not be protected effectively due to the very late starting grouting time. When the first grouting boreholes are arranged outside the boundary,the effect of reducing subsidence will be reinforced as the distance from the first grouting boreholes to the boundary is added,but will tend to be no increase as the distance is over the critical value(150 m). In addition,since the supporting effect of backfilling body limits the movement and deformation of overlying strata over the grouting horizon,along the overall length of grouting borehole,the horizontal deformation appears to be high in both ends and low in the middle, and tensile deformation and compressive deformation appears alternately.The layout principle of grouting borehole under the guidance of the technology of grouting backfill into isolated areas on stopping line has been successfully carried out in working face 7226 of Huaibei Mining Area. By arranging the first grouting boreholes 178 m and 147 m respectively away from the village-overlaid coal boundary,the coal mine has successfully implemented the project of grouting backfill into isolated areas without the removal of the village. The maximum horizontal deformation of village zone is 0.091mm/m,which is far less than the critical value(2mm/m) of Class I damage regulated by "Mine Regulations in three special condition". Besides,560 thousand tons coal have been safety excavated, and expected effect of subsidence control was achieved.