Experimental Study On Mining Effect And Gangue Pillar Stability Of Cutting Backfilling Mining Method

Aiming at the problem of insufficient filling mining materials,starting from the perspective of controlling mining subsidence,based on the domestic"mining-dressing-backfilling+X",constructional backfill mining and highwall mining abroad,a new mining method called cutting backfilling mining is proposed.The cutting backfilling mining method resources the part roof of the goaf as in-situ filling material,scientifically arranges the cutting area and the filling area,and develops a complete set of cutting backfilling comprehensive equipment to adapt to the mining stress and realize the partial filling of the goaf.Cutting backfilling method can achieve the goal of controlling surface subsidence on the basis of self-sufficiency of filling materials,and has a good application prospect.In order to verify the effect of the proposed cutting backfilling mining method and provide base for cutting backfilling design,a shallow coal seam Yangjiacun coal mine is selected as the engineering background.The research is carried out by combining similar material simulation,numerical simulation,theoretical analysis and the compression test of broken gangue,the failure characteristics,displacement and stress evolution process,distribution of fractures in cutting backfilling mining are obtained,the size effect,plane filling rate effect and deformation characteristics of gangue pillar of cutting backfilling mining are revealed,the characteristics of chain instability,the load response of gangue pillar is quantitatively analyzed,and the formula for calculating the backfill body's compression ratio(BBCR)of cutting backfilling mining is obtained.From this research,the main conclusions are as follows:(1)Similar material simulation contrast test of cutting backfilling method and caving method showed that the vertical displacement of cutting backfilling mining is 8.29%of that of caving mining method,and the horizontal displacement is 6.67%of that of caving mining method.The stress concentration factor is 56.00%of the caving mining method,which verifies the surface subsidence control and mining pressure reduction effects of the cutting backfilling method.Through the numerical simulation contrast test,it is found that the reduction range of different kinds of mining cracks in roof is about 2/3,which verifies the effect in inhibiting the formation of mining fractures of cutting backfilling.Further,the damage control effect and energy controlled release effect are put forward.Cutting backfilling mining can form transverse continuous and longitudinal coordinated whole deformation of overburden,thus realizing the damage control of surrounding rock.Cutting backfilling mining can reduce energy accumulation,reduce the total amount of energy release and prolong the release time,so it has the advantage of preventing roof disaster.(2)The simulation test of similar materials of cutting backfilling with variable parameters is carried out.Under the premise of mining-filling volume balance,filling thickness is the key parameter to determine the mining effect and the roof-contacted filling should be guaranteed first.On the premise of mining-filling volume balance and roof-contacted filling,numerical simulation of variable parameters is carried out.The mining thickness and filling width effects of vertical displacement and stress in filling area are obtained.In theory,the smaller the thickness of coal seam,the larger the height of cutting roof,the larger the filling width,and the better the effect of cutting backfilling.The correlation degree between the width of the cutting roof area,the width of the filling area and the roof displacement,the stress in the filling area is small.The correlation degree between the thickness of the coal seam and the roof displacement,the stress in the filling area is the largest.(3)The model of the elastic foundation beam with equivalent section of the first fracture of the roof is established.According to the geological conditions of Yangjia village,the initial fracture distance,position,energy distribution and energy release of roof before and after initial fracture are calculated.Among them,the critical plane filling rate of roof without breaking is about 57%,and the ultimate breaking size is 37.8m under the condition of roof cutting backfilling.For the same plane filling rate,the shape of relevant energy index curve of goaf is consistent with the deflection of roof;The shape of correlation energy index curve in front of coal wall shows exponential change law.With the increase of plane filling rate,the upper and lower limits of energy release density in front of goaf and coal wall decrease.(4)The compression test of broken gangue under different side limit constraints and the numerical simulation of unconfined broken gangue compression are carried out.Under the condition of unconfined constraint,the variation law of the residual height ratio with the ratio of height to diameter presents a cubic function,and shows obvious piecewiseness,especially when the ratio of height to diameter is less than 0.4,the ratio of residual height to height increases rapidly.The supporting effect changes the compression process,and the residual height and residual height ratio increase.Under the condition of fixed side limit,under the influence of load mutation or water,the broken gangue with stable deformation will still increase in deformation.At different side limits,the stress and strain of broken gangue more accord with the Terzaghi model.Broken gangue rheology is suitable for PTh rheological model under unconfined condition.(5)The similar simulation test and numerical simulation study of overburden instability in roof of cutting backfilling mining are carried out.It is found that the roof is the most easily unstable in the middle and end of goaf,and the instability of ore pillar in roof cutting filling stope has domino effect.There are three types of overburden failure spatial structure in the cutting backfilling stope.The overburden stress above roof stope is characterized by composite stress arch.Combined with the theory of structural mechanics,the instability of gangue column in key area and the load response near gangue column are obtained.The formula for calculating the backfill body's compression ratio(BBCR)of cutting backfilling is obtained.When the gravity of the overlying strata is small(within 4 MPa),the plane filling rate is more than 0.5,and the preloading stress is about 2 MPa,the BBCR can be guaranteed to be about 0.8.According to the results of this paper,the measures to improve the stability of the cutting backfilling system are put forward.