Experimental research on improving upper mining limit of fully mechanized caving face in rhin bedrock in yangcun coal mine

The paper probed the roof destroyed altitude by pouring water into borehole method after the coal stratum exploited in fully mechanized sub-level caving face in view of the situation in Yangcun Coal Mine,Ascertained the lying concealed small faults in the working face and their extension condition by underground radio-wave penetration method,Proved the thickness on shallow bedrock roof of No.305 face;On this basis,Designed dimension of the sand-preventing coal pillars,lifted the upper mining limit to 30m,Worked out one testing scheme for fully mechanized sub-level caving face.Have got success of improving the upper mining limit in Fully-Mechanized Caving Face in No.3 coal seam by the experiment.