Study On Roof Control Of 6m Large Mining Height Longwall Face In Shallow Buried Hard Roof And Hard Thick Coal Seam Face

In our country,the coal output of well mining in extra thick coal seam is over 40%of the total coal output,and the main mining technology is large mining height.The study of two hard(hard roof and hard seam)coal seams over 6.0m height and more than one coal mining is relatively few,so it is of great theoretical significance and engineering practical value to carry out the research.Based on the background of No.5-2 coal seam geological conditions in Zhang Jiamao coal mine,using the methods of rock mechanics experiment,numerical calculation,simulation and mining practice,combining the physical and mechanical parameters of coal seam is measured,and reveal the variation characteristics of the three-zone" overburden on.longwall face and the roof pressure is revealed the reasonable hydraulic support resistance and roof control measures in "two-hard" buried shallow thick coal seam 6.0m large mining height longwall face is determined.Research conclusions:(1)The lithology of the main roof of the No.5-2 coal seam is mainly fine-grained sandstone and siltstone,belonging to semi-hard rock.The uniaxial compressive strength of No.5-2 coal seam is 31.13MPa,tensile strength is 0.71MPa,which belongs to hard coal seam.(2)The first weighting step is 65m,the periodic weighting step average is 15m,the roof pressure is more violent.There is exists pre stress concentration of the longwall face,and a large number of tensile cracks appear in the front or the top of the immediate roof and main roof.The possibility of large roof cutting and caving above the longwall face is greater.If the support capacity and the rated working resistance are insufficient,the roof will cut down along the coal wall and so on,and the rated working resistance should be greater than 12000kN/frame.(3)Under the effect of bulking factor,the filling level of rock in caving zone is lower,and there has separation layer between upper layer and caving zone,part of cock in fractured zone turns into caving zone,so the development of caving zone is specific.In the shallow buried coal seam,the collapse fissure is easily to reach the ground surface.(4)Affected by hard coal seam and hard roof,the abutment pressure concentration degree of longwall face is high,and the peak value of abutment pressure is located in the 10?13m ahead of the coal wall.Based on this,the reasonable coal pillar width between the withdrawal channels of the working face is 55~60m.(5)According to the geological conditions and roof pressure the ZY12000/28/63D supports are adopted in 15201working face in No.5-2 coal seam in Zhang Jiamao coal mine.It can be realize safe high production and high efficient mining.