Study On Optimum Thickness Of Covering Layer During Turning Open Pit Into Underground Mining

At present, the majority of our medium and large-scale open-pit mine has been the advanced stage of mining, due to the different conditions of the ore bodies buried, part of the open pit mining method will be converted into a depressed mining, underground mining. Throw buried ore bodies at the bottom of the open pit, and this part of the ore body Sublevel caving mining from open pit to underground mining mine, to cover a layer of gravel in the bottom of the pit overburden, from the better weatherization put air leakage, stagnant water, the formation of extrusion blasting ore and the end conditions, and anti-shock pressure. Thickness of Covering Layer study from open pit to underground mine production safety is important.Combined with the function of the cover layer, the thickness of the cover layer According to the characteristics of the Shibao iron ore from open pit to underground mining, ore process, use loose ellipsoid theory, calculated analysis of the structure and thickness of the cover layer change with the release of the changes in the amount of ore, its sphere of influence depends on the ore loose ellipsoid height, the height of the cover layer is about release2.5times the height of the ellipsoid. Shibao iron ore from open pit to underground development Sublevel caving method in the design of ore a height of10m, Shibao iron ore from open pit to underground lowest overburden thickness should not be less than25m.The the PFC2D software on the Shibao iron ore process simulation, the covering layer down process, the moving velocity of the rock in the the ore discharge funnel in the axial direction, the moving speed is less than the coarse particles covered rock fine particles covered rock mobile speed. Therefore, if the cover layer and the ore body at the junction between the block of rock is too small, in the process of ore will lead ahead of dilution of the ore. Caving ore than underground mining stopes in the cover layer and the ore body interface between the overburden rock block average block, to prevent ahead of ore dilution occurs. In addition, the study of30m,40m thickness of the cover layer ore overlay interface changes30m thickness of the cover layer interface changes in the process of ore larger, smaller40m thickness of the cover layer interface changes, both formed a fall funnel and ellipsoid, loose the ellipsoid theory.Finally, to verify thickness of30m and40m thickness of the overburden pressure of the anti-shock capacity, by derivation, the impact of the fall by30m thickness of the overlay buffer pressure3.37MPa than the ore layer can withstand the maximum stress value of3.16MPa large, so the ore layer can not withstand the pressure of a huge impact arising damage. Overburden thickness of40m buffer the impact pressure of2.25MPa, compared with the ore layer can withstand the maximum stress is small, the ore layer does not occur destroyed, to ensure the safety of underground production.40m thickness of the cover layer can play the role of anti-shock pressure.Shibao iron ore from open pit to underground Covering Layer thickness of40m is recommended. In order to improve the balance of the rock slope mining waste rock in the mining process continue to backfill the space formed covering layer down, keep the top elevation of the cover layer is always greater than1476m above sea level, in order to enhance the slope rock mass support to prevent slope sudden large range of slip.