| With the gradual depletion of coal resources in the central and eastern regions,the coal energy in the west has a long-term development opportunity.Mine in Guizhou province as a typical region,mostly in low and medium ridges ridge landform,geologic structure is extremely complex,and coal seam occurrence layers,due to long-term extensive management mode of coal mining enterprises,it leads to a series of environmental problems such as surface subsidence or mountain slide and coal gangue pollution.Solid waste paste filling mining is a green mining method with high resource recovery,which can effectively control the migration of overlying strata and surface subsidence,and is a key technical means to realize the safe and efficient mining of"three under"coal pressing and other residual resources.At present,it is difficult to popularize backfill mining in Guizhou mining area,because the cost is too high.The demand for filling raw materials,the throughput of materials and the complex and inefficient filling process are the main reasons for the high filling cost.In view of the problems faced by the current coal mine filling mining,several scholars have found that local filling mining can reduce the filling cost in a disguised way.Guided by strata control and fracture evolution,this paper adopts two local filling mining methods to control the key stratum and the direct roof respectively.The former belongs to the"mining-leaving-filling"mining mode,the latter is Tai Yuan university of technology professor poems it puts forward the model of the structural formula of filling mining.The control of overlying strata and surface subsidence is realized through local filling mining.Meanwhile,the solid waste filling materials with gangue and fly ash as aggregate are studied by using local materials to further reduce the filling cost.Through field investigation,the paper simply analyzed the distribution of surface load and the principle of local filling technology,analyzed the optimized ratio of solid waste filling materials and the evolution law of mechanical strength through indoor test,and tested the mechanical parameters of coal rock mass and filling body.FLAC3Dnumerical simulation software was used to systematically analyze the influence of local filling mining scheme on the migration law of overlying strata under the local filling mining in Guizhou ridge landform,and the discrete element simulation software UDEC was used to analyze the space-time evolution law of surrounding rock stress and fracture during mining stage.The main contents and results are as follows:（1）According to the theoretical analysis,the surface load corresponding to the11071-filling face is"M"shaped linear load.In order to ensure the stable bearing of the carrier to the overlying rock,the compressive strength of the backfill body is preliminarily calculated to be 5.55Mpa～7.4Mpa.Through laboratory test analysis,the optimal ratio of paste filling material is A3B3C3,namely slurry mass concentration 80%,cement content 12%,fly ash content 25%,compressive strength 6.8～7.1MPa.SEM results showed that the hydration reaction was slow in the early stage.With the growth of the age,the hydration of cement gradually occurred,and the C-S-H gel crystals generated by the reaction gradually increased,which bonded the dense skeleton structure into a whole.Meanwhile,the active components of fly ash were gradually stimulated,which promoted the hydration reaction and improved the filling strength;（2）Based on FLAC3D numerical simulation,"mining strip 35m,retaining coal column 30m,replacement rate 25%～50%"is the most reasonable scheme in displacement strip coal pillar mining.There is no"wave-shaped"settlement on the central surface,and the secondary deformation of the surface is not obvious,which meets the building damage grade I standard.Affected by the surface load,the vertical stress borne by the underside of the mountain is the largest;（3）Based on FLAC3D numerical simulation,the direct roof subsidence of strip structure filling is slightly larger than that of full filling,presenting a"wave"subsidence,and the foot area is the largest subsidence area.With the decrease of the filling strip spacing,immediate roof subsidence decreased from 15 mm to 6 mm maximum,"wave"subsidence trend gradually stabilized,empty region of area above the stress of 0gradually disappear,pack on either side of the edge stress concentration degree decreases gradually,the vertical stress is gradually transferred to the central filling body,is advantageous to the"filling strip-direct roof"composite structure stability.Finally,"3m interval filling 3m"is determined as the optimal filling scheme in this paper,it is closer to the control effect of all filling on roof and surface.（4）Through UDEC numerical simulation,during the filling mining stage of No.7coal seam,cracks on both sides of the hollow roof area under the mountain are relatively dense,with a few cracks running through each other,and there is a risk of gangue falling on the false roof.The stress concentration of the front coal wall presents a trend of"increase-decrease-increase".The direct roof stress curve in the middle of the stope shows a gradual"cycle",and the stress peak curve changes from"increase-decrease"to"increase-decrease-increase-decrease".The maximum peak stress of the stope is3.4Mpa,located at the bottom of the mountain,45m and 255m away from the cutting hole.The stress valley values are in the range of 0.2-0.5Mpa,and there is no"0"stress zone.As the elevation of overlying strata increases,the strata tend to the stress state of original rock.（5）In order to further maintain"pack-direct roof"the stability of the composite bearing structure,control overburden migration of locally filled stopes under ridge landform,should be combined with"even pick even charge"technology to improve the original filling process,reasonable use of mine waste steel to improve the mechanical properties of solid waste filling body,at the same time,in view of the mountain area of stope part for special treatment. |
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