Study On Laws Of Strata Behavior And Top Coal Cracking Of Fully Mechanized Top Caving Mining Face With Large Mining Height In Extra Thick Coal Seam

During the recovery period of Tongxin mine quarrying thick coal seam of Carboniferous in Datong mining area,the mineral pressure appears strongly,and top coal broken seriously.Therefore,the characteristics of underground pressure and the laws of extra thick coal seam breakage in fully mechanized top coal caving face under hard roof condition in Datong mining area are studied,so as to provide theoretical guidance for safe and efficient mining of extra thick coal seam in Datong mining area.In this paper,the actual conditions of 8202 fully mechanized working face of Tongxin mine as the project foundation,with the research methods of laboratory experiments,field measurement,theoretical analysis and numerical simulation method,this paper analyzes the bearing characteristics of the support in fully mechanized caving face,the law of the top coal failure,the law of the overburden movement and the stress distribution of the top coal during the advancing of the working face.The main results are as follows:(1)The results showed that average first weighting interval of the working face was 23.5 meter,and the average periodic weighting interval was 13.8 meter.It showed that the upper part was strongly pressurized,but the middle and lower parts were pressurized and relaxed.High stress areas were mainly concentrated in the upper and middle part of the working face,during the face roof periodical pressurized period,the maximum working resistance of support accounted for the support rated working resistance of 87 %,showed that the face support could basically meet the requirement of roof control.There was a high correlation between the setting pressure and end resistance,it could be concluded that the resistance distribution at the end of the stent was significantly affected by the setting pressure of the stent.During the mining period,the leading influence area of the working face was about 140 meter,the violent influence range was within 80 meter.Measures such as increasing setting load,accelerating the speed,and during the period of strong pressure,no coal caving or less coal caving to control the roof could effectively alleviate the strong pressure at the working face so as to provide the guarantee for the safe and efficient mining of the mine.(2)A comprehensive analysis of the supporting pressure of the working face,the roof migration(separating,slewing and sinking),and the repeated support of the supports together to promote the crushing of the top coal is made by the three actions.One of the support pressure on top coal fragmentation plays a key role,which makes the horizontal displacement of the top coal increased rapidly,the original crack has been further extended,the upper coal pre crushing;migration from one side to the roof goaf of coal body constraint further weakened in fissured coal is fully extended the support bracket;repeatedly and mobile,can increase the damage degree of the lower top coal,greatly reducing the formation of large scattered coal caving mouth blocked the opportunity to fully break into granular coal.(3)The numerical study shows that along with the advance of working face,the rear bracket top coal broken into dispersion along the stacking bracket tail beam and the goaf formed body is like a funnel is slowly released,the initial direct roof cantilever structure has a certain working face;continue to promote the large sandy mudstone fracture,rotation sinking,can not form a bearing structure;support pressure increased significantly,the top coal recovery amount will increase;when the working face advances to 25 m thick hard sandstone,bending and sinking,separation between layers,when the working face advances to 30 m thick hard sandstone bending and instability,the formation of masonry structure,the bearing capacity weakened further,and top coal direct roof load is more intense,the broken coal range increased,a higher degree of fragmentation.