Study On Instability Mechanism Of Floor Coal And Rock Pillars In Upward Mining Above Goaf In Yuanbaowan Coal Mine

There are coal and rock pillars in the room-and-pillar mining goaf,although the coal and rock pillars can control the surface subsidence and restrain themovement of the strata,the existence of the coal and rock pillars in the room-and-pillar mining gob of the lower coal seam may reduce the safety of the upper coal seam fully mechanized upward mining above goaf working face.In this paper,No.6 coal seam in the study area No.6107 fully mechanized upward mining above goaf working face has the threat of flight.The mining of No.6107 fully mechanized upward mining above goaf working face will not only destroy the surrounding rock structure of the coal seam,but also destroy the stability of the coal and rock pillars in the room-and-pillar mining goaf of the lower No.9 coal seam,once the coal and rock pillars in the room-and-pillar mining goaf is unstable,it will inevitably affect the safety of No.6107 fully mechanized upward mining above goaf working face.In this paper,based on upward mining above goaf in Yuanbaowan Coal Mine,Shuozhou,Shanxi Province,the methods of similar material simulation,field measurement and UDEC numerical simulation are used to study the stability of coal and rock pillars in the room-and-pillar mining goaf and the influence of the failure and deformation of the coal and rock pillars in the room-and-pillar mining goaf on the No.6107 fully mechanized working face.Based on the study of the instability mechanism of the coal and rock pillars in the lower coal room-and-pillar mining goaf caused by upward mining above goaf in No.6 coal seam,this paper explores the instability law of the coal and rock pillars and the specific methods to solve the instability of the coal and rock pillars.The main research results are as follows:(1)By using UDEC numerical simulation software,the influence of No.9 coal seam on No.6107 fully mechanized face under different mining width and filling height is simulated.The results show that: before No.6 coal seam mining,when the room-andpillar mining width is 12 m,the coal and rock pillars is stable;after No.6 coal seam mining,compared with the mining width of 13 m,12m,11 m,when the mining width is 10 m,the coal and rock pillars in the room-and-pillar mining goaf is the least damaged,the coal and rock pillars tends to be stable,and the maximum advance distance of coal seam 6 working face is 85m;after No.9 coal seam goaf is filled,through the effect comparison between different schemes,it is found that when the filling height is 7m or above,the coal and rock pillars in the room-and-pillar mining goaf is the least damaged The stability is good.(2)Through the simulation test of similar materials,the influence of No.9 coal seam on No.6107 fully mechanized face of No.6 Coal seam is simulated under the condition of a certain mining width and a certain filling height.The results show that under the same test conditions,the coal and rock pillars width is smaller and more prone to failure and instability.When the No.6 Coal seam is mined to 65 m and 75 m respectively in model 1 and model 2,the coal and rock pillars is damaged,and when the filling height is 7m,the coal and rock pillars in the room-and-pillar mining goaf of No.9 coal seam is stable.(3)The peep results of grouting and drilling in the upward mining above goaf working area of No.6107 fully mechanized working face,it shows that the filling effect of No.1,No.2,No.3 and No.6 holes is good.The filling height of the old goaf near hole 5 is about 2m,indicating that the filling effect of the old goaf is general.There are nearly 4m filling cavities not connected to the top near the No.13 hole in the old goaf,which indicates that the filling effect here is not good,which will inevitably have a certain degree of impact on the safe mining of the No.6107 working face,so prevention and control measures should be taken in advance.(4)The comprehensive analysis of UDEC numerical simulation,similar material simulation and field test results shows that when the filling height is up to 2m and below,the No.6107 fully mechanized working face will not cause the instability of coal and rock pillars in the No.9 coal room-and-pillar mining gob,and the old goaf is basically stable.There are 59 figures,9 tables and 98 references in this paper.