Study On The Development Characteristics Of Overburden Water Flowing Fracture Zone In Shallow Coal Seam Group Of Hongliulin Coal Mine

The shallow coal seams of the Jurassic coalfields in northern Shaanxi are abundant.With the consumption of coal resources,the coal mines in the Shennan mining area gradually used the mining of multiple coal seams method.The mining poblems for example roof pressure,air leakage,water inrush and surface damage of the coal seam group are highlighted.The laws of overburden caving and fissure development are the basis for revealing the mechanism of roof weighting and safe-green mining,which needs to be studied.This paper based on the mining conditions in shallow coal seam group of 4^-2?upper seam?and 5^-2coal seam of Hongliulin Coal Mine.Through the field measurement,physical simulation,numerical simulation and theoretical analysis methods,studied the development law and characteristics of overburden water flowing fracture zone?WFFZ?in shallow coal seam group of Hongliulin Coal Mine.The development height of the WFFZ is restricted by the key stratum of the overburden rock,and it is related to the tensile strength of the key stratum,the resistance of the soft rock stratum,the free space height of the lower part of the rock layer and the propulsion distance of the working face.Using the key stratum theory to determine key stratum and analyse the limited distance of different rock layers,giving a computational formula of the height of the WFFZ.According to site observation of drillhole SK1 and SK2,the WFFZ was obtained,and the overburden caving height was observed through various site observation methods.The results show that the fractures develop in bedrock and soil layer after 4^-2coal seam mining,according to observation of drilhole SK1,the height of caving zoneis 16.4m,the ratio of which to mining height is 5.7.According to observation of drilhole SK2,the height of caving zone is 15.5m,the ratio of which to mining height is 5.4,and the average ratio is5.5.According to site observation,the first weighting intervalof 4^-2coal seam faces is55⁶6m,and the average periodic weighting interval is 16.13m,the periodic weighting strength of main roof is 35⁴1.7MPa.The first weighting interval of 5^-22 coal seam faces is63⁶8m,and the periodic weighting interval is 14.03m,the periodic weighting strength of main roof is 28.5⁴6.4MPa.The weighting interval of lower coal seam faces decreases,the difference of weighting strength are increased.The law of overburden collapse caused by physical similarity simulation and numerical calculation is basically consistent with the field measurement.The research shows that the height of the caviing zone of the 4-2 coal seam is 14.5¹5.8m,the ratio of which to mining height is 5.05⁵.5.After the overburden is stabilized,the height of the fracture zone is 91m,the ratio of which to mining height is 31.7.The height of the caviing zone of the 5-2 coal seam is 26.4m,the ratio of which to mining height is 4.4;the development height of the fracture reaches the surface,the ratio of which to mining height is 31.7.Through the research,the law of overburden caving in coal seam group mining is mastered,and the development height of water flowing fracture zone is obtained,which provides a theoretical basis for high-efficiency green mining of coal seam group in Hongliulin coal mine.