Study Of Mining Subsidence Of Shallow Buried Coal Seam Under Different Mining-filling Methods

The in-situ rock mass stress is destroyed by underground mining,and the stratadeformation is transmitted to the surface in some way.The surface subsidence has becomeincreasingly seriously in recent years, which has an effect on people who lives in mining area.Surface subsidence not only can reduce the cultivated land, but make the buildings lean,evendamage. For shallow coal seam, this phenomenon is particularly prominent.At present, thepaste filling mining, strip mining and the replacement mining are gradually becoming aneffective way to ease the surface subsidence.Paste filling is not only an efficient solution of mining subsidence and surfacedamage,but also can effectively reduce the coal waste piling. The controlling effect of thesurface subsidence and filling are determined by mechanical properties and deformationcharacteristics of paste filling material. The surface deformation and the long-term stability ofpillar are depend on the suitable mining width in strip mining.Replacement mining which isbased on the theory of load displacement can not only ensure the surface deformation withinthe building level I,but can maximize the coal pillars in suitable packing material ratio.Therefore, paste filling materials with swelling properties,theoretical analysis on reducingsubsidence mechanism of each sink reduction method for shallow coal seam and thenumerical simulation abut the three methods research are researched systemically.The main contents and results are as follows:(1) The paste filling materials with swelling properties are prepared in the lab. The ruleon the expansion ratio,compressive strength, shearing strength, tensile strength, angle ofinternal friction and the cohesion of paste material changed with the bentonite content areanalyzed.The experiment show that adding some bentonite in the paste material can improve the expansion rate of filling body.However bentonite can reduce the compressive strength ofpaste material.When the quality ratio between bentonite and cement is0.6,the rate ofexpansion is2.25%and the compressive strength of the paste material in28days is4.85Mpa.(2) Based on the geological conditions of the western mine, the completely fillingmining of18112working face is researched by numerical simulation in different mechanicalparameter.Results show that the influence of the rate of backfilling-body-height tomining-height in controlling surface subsidence is greater than the strength of filling body.With the increasing of the ratio between bentonite and cement,the surface deformation, thevertical stress of strata and the overburden rock damage area all decrease.When the qualityratio of bentonite to cement is60%, the strata stress is the closest to the in-situ rockmass stress and the surface deformation is within the building grade I.(3) Different strip mining schemes are designed based on the theory of strength on thecoal pillar. The simulation results show that when the surface subsidence are no waves andthe deformation is within the building grade I,the mining width and the leave width areseparately30m and35m.Meanwhile,the safety coefficient of coal pillar is the biggest,and thecoal pillar can maintain the long-term stability,and the extraction rate reaches53.8%.Thestrata height above30m of model is in the original rock stress state.There exists increasedstress zone on the coal pillar and reducing stress area above the goaf.The range of the originalrock stress is bigger with the leave width.Edge of the pillar has been destroyed, and the stressis0Mpa. From the edge of pillar to the distance of5m, the coal pillar only has residual stress.The maximum stress of coal pillar is on the edge of the distance of5m,and the pillar hasminimum stress in the center,even the yield zone of coal pillar does not change along with themining width.(4) The replacement mining show that when the packing height is4.5m,that is the fillingbody can completely meet the top, the coal pillar of30m can be fully replaced coal pillar. Thevalue of surface subsidence is almost equal to strip mining.When the filling body can’tcompletely reach the roof, the surface deformation is greatly increased after replacementmining.When there leaves5m coal pillar in each side, the filling height add from4.3m to4.4m,meanwhile the vertical stress’s distribution law is similar to strip mining.The value of surface deformation is larger to strip mining,but it still less than the building level I,whichshows that the roof falling is effectively controlled by the small coal pillar.