The Gas Migration Law And Extraction Method Of Close-distance Coal Seam Mining In Hexi Coalmine

As the close layer is mined, large number of crack developed in adjacent rock.Then, pressure relief in protected layer, plenty of gas desorb and goes into theunderlie layer through cracks. Due to leakage, air in workface get overrun of gas,threatening the safety of mining of protective layer. Taking Hexi coalmine geologicalconditions as background, this paper do some research on layer stress distribution andthe gas concentration distribution, under different ventilation modes and extractionmethod. Applied Y-type ventilation in engineering, combined with the gas controleffect, this paper provides an example for coalseam with similar conditions.During the mining of overlying layer the change of the vertical stress of nearbyrock obtained by numerical simulation. After overlying layer mined, bottom stressdistribution law is compression-unloading expansion recovery, and it revolves as faceforward. Be overlying layer bearing stress distribution is an approximation M. Whenmining range of200m, maximum vertical stress is33MPa, the relief range of pressureis120m, unloading area vertical stress is1MPa and best unloading area is under theoverlying layer goaf. Relative compression deformation is4.3‰in underlie-seam,maximum relative expansion deformation is7.6‰.Through the analysis of the gas concentration distribution rule under differentventilation system, the best ventilation way is U-type ventilation with high-levelsuction tunnels and Y-typed ventilation. According to HeXi coalmine geologicalcondition, Y-type ventilation mode is chose. Through research, this paper gets gasdistribution law in Y-type ventilation workface. Gas distribution is reduced after thefirst rise trend along the face tendency, the gas concentration variation from0.5%to0.55%in the entry. High gas concentration area concentrated in deep-goaf and in themost of shallow area is below25%.In3311workface, which use Y-type ventilation, this paper design the gasextraction system. Through comprehensive extraction, gas concentration is controlledfrom0.2%to0.7%, in workface and goaf-side entry. Face drainage rate is roughlybetween30%and70%, which average is55%. Windblown mine gas quantity is up to14m3/min, and tends to be stable at around4m3/min at the later period. Whenmining3311workface,8.145million m3of gas was drained overall.Gas concentrationin drainage branch pipe of material lane and transportation lane is steady around 6%-10%. And it in drainage branch pipe of goaf-buried pipe is about3%, fissure zoneis around4%-10%. In the underlying4#seam, gas pressure reduced from0.79MPa0.21MPa, gas content reduced from7.95m3/t down to2.3m3/t. Return air and workingface gas concentration always comply with safety regulations, ensuring the overlyinglayer in safety situation.