Research On Structural Backfill Mining And Roof Stability Control At The Terminal Mining Period

Due to the severe dynamic pressure during the terminal mining period,the surrounding rock deformation and damage are serious.It is necessary to keep a large end-mining coal pillar to ensure the smooth progress of withdrawal the powered supports at working face,by recovering end-mining coal pillar and constructing the space during the terminal mining period,not only can it improve the stress environment during withdrawal the powered supports at working face,but also can realize the use of underground space.Taking the Dengmaotong Mine as the engineering background,this paper uses theoretical analysis and numerical simulation to analyze the roof stability,breaking mode,abrupt instability law,and parameters of the isolated body for space construction,the reasonable parameters of the isolated body reserved are determined,And analyzing the economic benefits of recovering end-mining coal pillar and underground space utilization during the terminal mining period,The following conclusions are drawn:(1)Analyzing stability and breaking rules of the roof,and combining with the geological conditions of Dengmaotong Coal Mine,it is concluded that the roof strength is moderately stable and the breaking method is "O-X".At the same time,a mechanical model of inclined isolated body is established.Based on the analysis of the stability of the roof,the calculation formulas of the support strength and cutting resistance of inclined isolated body were derived,It was found after analysis that the change law of the cutting resistance and support strength of the inclined isolated body with the length of the flap top and the width of the isolated body.Considering factors such as the filling material of inclined isolated body and the safety factor,it is concluded that the inclined isolated body is arranged in a range of 3-6 m of flap top,and the width of the isolated body is 3m,and the water-cement ratio of the filling material is 1.5: 1.(2)Based on the analysis of catastrophe theory and strength reduction method,defining the reduction factor when the catastrophe instability of the suspending roof is the safety factor of the suspending roof,establish a cusp catastrophe model,and use the displacement catastrophe of the suspending roof to indicate the catastrophe instability of the suspending roof.The relationship between the reduction coefficient and the maximum displacement function of the center of the suspending roof and the criterion equation for the sudden instability of the suspending roof are deduced.Combined with the geological conditions and numerical simulation of the Dengmaotong coal mine,the safety factors of different suspending roof lengths are obtained.By analyzing the change law of the safety factor of the suspending roof with the length of the suspending roof and considering the influence of factors such as mining,a reasonable length of suspending roof was determined to be 6m.(3)Through numerical simulations,the effects of the strength,width,and spacing of theisolated body on the bearing capacity and deformation failure of the isolated body and roof when the structural isolated body are oriented and inclined are studied.It is concluded that as the strength and width of the isolated body increase,As well as the decrease of the spacing,the bearing capacity of the isolated body and the roof is continuously enhanced,and the deformation failure are reduced,which is beneficial to the stability of the underground space;Considering the utilization rate of the underground space at the same time,when the structural isolated body are oriented and inclined,determine the water-cement ratio of the separator is 1.5: 1,the width is about 3m,and the spacing is about 3-4m.(4)Based on the geological conditions of Dengmaotong,Two schemes were designed to stop coal mining pillar recovery and underground space construction within 60 m of the stopping line.Through analysis of the economic benefits of the two schemes,It is concluded that scheme1 and scheme 2 achieve total economic benefits of 746.182 million yuan and 771.624 million yuan respectively.The value of recover the end-mining coal and underground space utilization during the terminal mining period is significant.The paper has 47 pictures,18 tables,and 90 references.