Research On Law Of Fracture Development Of Shallow Seam Mining Through Ravine

The coal of the northern Shaanxi area of China is abundant,and the coal seams in this area are shallow,the bedrock is thin,and the surface ravines are vertical and horizontal.With the increase of mining,especially when mining through valleys,mining cracks will cause a series of problems that restrict the safety of mine production,such as air leakage and water leakage.Therefore,based on the influence of the development of mining cracks in thin bedrock and thick loose layers in northern Shaanxi,studying the development law of mining cracks in gully will help the safe mining of shallow coal seams under the "gully".Based on the engineering background of the mining of 1-2 coal seams in Nanliang,a typical shallow coal seam with special topographical characteristics of the "gully",this paper studies the development of cracks in the shallow coal seam mining through the gully,and summarizes the development law of mining cracks in shallow coal seams mining through the valley.Three methods are used to study the crack development law during the mining shallow coal seam passing the "gully",and the following laws are obtained:(1)The position of the"Ascending" crack is in the same position as the periodic weighting point,the width of the cracks will first become larger and gradually decrease after being penetrated,and the distance between the adjacent crack is inversely proportional to the buried depth of the coal seam;(2)"Downward" cracks will have different characteristics when mining though "gully".The crack will lag the working face when mining down the slope,and the crack will advance the working face when mining up the slope.The distance of lagging and leading is the distance of one cycle.The width of the "Downward" cracks will first become larger and gradually decrease after being penetrated;(3)The type of crack after penetration is a vertical crack,and the width will stabilize to a certain value and no longer change when the advancement of the working face is compacted.(4)During the mining,the crack width at the midpoint of the slope and the crest will be larger than other parts of the "gully",and the degree of disaster will be deeper;cracks will be compressed and closed even raised at the bottom of the gully.Based on the analysis of the crack development law of shallow coal seam miningthrough the valley,the following preventive measures are proposed for possible safety problems:in the process of mining through the valley,the prevention shall be delayed during the downhill phase;Take advance preparation and prevention work at uphill stage.In response to underground air leakage and other dangerous situation restricting production,the cracks should be blocked after two cycles of pressure,and data such as air leakage is intensively monitored and prevented.These measures can prevent the hidden dangers and problems caused by the mining of the valley,These measures can prevent the disasters caused by cracks in advance and promote the sustainable development of shallow coal seam mining under valley.