Experiment Study on Top Coal Weakening with Deep Hole Blasting at Initial Mining Stage of Fully Mechanized Top Coal Caving Mining Face

In order to solve the high overall top coal strength,poor top coal falling and difficult top coal caving problems at the initial stage of No.3306 coal mining face in Xinglongzhuang Mine,before the mining operation of the coal mining face,a deep borehole pre-fracturing blasting and a breaking blasting trial of top coal and roof at the open-off cut of the coal mining face was conducted.The deep borehole pre-fracturing blasting had improved the crake development degree of the top coal and reduced the broken lump coal size of the top coal.The top coal caveability was improved.The cracking free face formed in the strata above the roof by the breaking blasting in the top coal and roof above the open-off cut could make the roof bending and breaking in advance and could reduce the step distance of the initial strata pressurization.With the above method,the top coal recovery at the initial mining stage could be improved from 45% to 75% and the initial step distance of the direction roof and the main roof could be reduced by 40.4% and 36.6% individually.Thus,with the forced caving,the top coal could be fully recovered before the initial strata pressurized and the top coal mining recovery rate at the initial mining stage of the fully mechanized top coal caving mining face could be effectively improved.