Study On Effection And Range Of Mining Under Protection Layer In Dashu Coal Mine

The coal mine gas outburst accident is the focus of mine gas disaster. It is leaded tosome serious problems so people must take some measures to hinder. Ones of methods，Protective layer mining,is considered to be the most economical and effective method.In this paper,have studied on effect and scope of mining the under protection layerprotection. Constructed nine drill field total workers in50drill holes.Study on the changeof pressure,amount of expansion,permeability coefficient,borehole gas flow, gascontent.The ultimate goal is to study the protective effect, in order to determine the scopeof protection for the safety and efficient mining services. Point out protective layer hadbeen mining the scope of protection’s original coal seam gas pressure can reduce about0.5MPa; the permeability coefficient increase in777.1times and the inclined upper portionof the maximum increase of1552times,the lower maximum increases1135times.The bestpermeability region is about80m, generally is ahead of working face12m and back ofworking face68m. Maximum expansion ratio reached23.7‰,ahead of working face60mwhere appears at the largest amount of expansion; The original gas content of2#coalseam is10.26m~3/t,after mining the4#coal seam the residual raw coal gas content isreduced to6.04m~3/t and reduce41.1%,from the loss,the desorption amount,the mainlyreduce the loss by analysis on residual,the relative decrease of94.6%，parsing the amountof the relative decline of1.3%,and the remaining amount of the relative decline of19.1%.Proven the relief angle of the upper part allown tilt direction is δ2=90°,the underpart is δ1=75°,the relief angle of strike direction is δ3=65°.The interlaminarmaximum vertical protection distance is96m,minimum vertical protection distance is9.4m.Based on above research，the maximum scope of protection on upper and underallown tilt direction is93.10°and78.60°,the maximum scope of protection on strikedirection is67°.