Study On Overburden Movement And Gas Migration Law After The Destabilization Of Coal Pillar In The Goaf

After the coal mining,there is a large amount of gas resource in the goaf.Studying the overburden movement and gas migration law in the goaf is of great significance for the exploitation and utilization of gas.By comprehensive use of laboratory test and numerical simulation,research is carried out on the scientific problems such as overburden movement and gas migration law after the mining of adjacent working faces and after the destabilization of coal pillar.The main research contents and conclusions of the paper are as follows:(1)The similar material simulation test is carried out on the overburden movement after the destabilization of coal pillar in the goaf,and the evolution laws of stress,fissure and displacement of the overburden of the adjacent working faces before and after the destabilization of the coal pillar are obtained.At the stage of the stability of the coal pillar after the mining of adjacent working faces,the overburden above the coal pillar does not have a large overall movement,forming two goafs with close caving height.When the coal pillar is unstable,the upper overburden moves downward as a whole,partial fissures are compacted,the upper strata is broken,and the two small trapezoidal arch structures are combined into a large trapezoidal arch structure.(2)The characteristics of the overburden fissure in the goaf after the destabilization of coal pillar are analyzed.The change of crack ratio and fractal dimension is studied.The characteristic parameters(area,length,width,dip angle,et al)of overburden fissure are statistically analyzed.The areas with large changes in the characteristics of the overburden fissure before and after the destabilization of the coal pillar are mainly concentrated on the two sides of the overburden with inverted trapezoid above the coal pillar.The closure of the fissure in this area causes changes in the separation ratio,fractal dimension and characteristic parameters.(3)Based on the fissure field obtained from the similar material simulation test,Numerical simulation of gas migration is conducted respectively for the two cases after the mining of adjacent working faces and after the destabilization of coal pillar,and the gas migration law in the goaf is analyzed.As time goes by,the gas in the coal pillars and residual coal is desorbed and flows into the fissure field.The gas pressure in the coal pillars and residual coal decreases accordingly,and the gas pressure in the fissure field first increases and finally stabilizes.The reason for the different gas migration laws before and after the destabilization of coal pillar is that the fissures generated by the destabilization of coal pillar connect the two goafs.This paper has 65 figures,10 tables and 68 references.