Technical Basic Study On Cutting Seam In Mining Lane's Roof To Reduce Width Of The Coal Pillar Of Protected Lane

During the coal mining, in order to protect the road and manage the roof, all kinds of coal pillar are always left which are the major source losses of underground resources. Especially in recent years, in the geological conditions of the coal seam with one or several hard rock stratums, and with the improvement of mechanization, and the increase of mining height in working place, the expansion of the mining area and the increase of the concentrated stress in the coal pillar with the mining roadway, and the larger distribution, it leads to the big coal pillar in the mining lanes. As for the high gas mine, in order to meet the safety requirement, the working face is decorated by the way of "two into two out" or "three into and two out". In order to reduce the rate of tunneling, one or two mining lanes are reserved for the next working face in case the mining face is influenced—the width of the one side for the protection lane coal pillar is up to50m, which caused the width problem of the coal pillar in the mining lane to be more obvious. Besides, these coal pillars are difficult to be recovered, which leads to the decline of the rate recovery in mining and the great losses of coal resources. Therefore, the technical basic research of reducing the width of the coal pillar is a scientific problem and urgent need of the national economic and social development, which has important scientific significance and wide application.The decrease of the coal pillar of protected lane depends on the lateral stress concentration during the mining. At the same time, the stress concentration depends on the thickness and strength of the coal seam mining, and the structure of and mechanical properties of the roof and floor in the coal seam rock and the structure of the roof after collapse, and other factors. With the increase of the mining height, the fall coal gangue is difficult to fill the goaf, so the roof with a certain Angle tilt to the gob side. Then the lateral stress concentration increases, the coal pillar edge is damaged, and the concentrated stress transfers to the coal seam side, and at last the width of the coal pillar increases. Therefore, to ensure the safety and effectiveness of reducing the coal pillar width, the control of the lateral concentrated stress is very important. According to the stress distribution caused by the mining, we advises that the pre-split blasting cut seam method is used to transfer the concentrated stress (near mining face roadway the roof along the edge of roof to cutting the vertical seam), that is, pre-split blasting cut seam mining method is used to weaken the effect of the stress to transfer and reduce the width of the coal pillar. According to the geological conditions of ZhaoZhuang Coal Mine, the theoretical analysis, the laboratory model test and the numerical simulation have been adopted. The formation structure of the roof breaks, the fall deformation characteristics, the surrounding rock and the lateral stress distribution law of coal before sewing and back also have been studied. At last the main conclusions as follows:(1) When the roof is not cut and the collapse coal gangue does not fill the goaf, the lateral roof is in a state of cantilever, which can be simplified as a cantilever beam structure. When the mining roof is cut and the collapse coal gangue fills the goaf, the lateral roof under the support of the coal gangue can be simplified as a cross beam structure.(2) According to the structure of the lateral roof, through the force analysis, the mechanical model of the lateral additional stress concentration is established and the concentration stress formula which made by the movement of the lateral roof, and before&after the seam is cut in the coal mining face is acquired: When it is not cut: After it is cut (the collapse coal gangue fills the goaf):(3) Based on the geological conditions of ZhaoZhuang Coal Mine, the similar simulation experiment and numerical simulation have been adopted to study carving characteristics of the roof under the different cutting seam depth, the stress distribution on the coal pillar and overlaying strata. The results showed that, the cutting seam depth is used as vertex of the fall Angle, with the increased depth of the cut seam, the fall Angle gradually reduces. When the seam is not cut, the fall Angle is61°. When the cutting depth is15m, the fall Angle is37°. When the cutting depth is20m, the fall Angle is33°. With the increased depth of the cut seam, the peak stress of the coal pillar and the average stress decrease, and the peak stress position is gradually nearer to the edge of the goaf. Compared with no cutting, when the cutting depth is15m, the peak stress and average stress reduce most, that is, reduce by46.5%and48.3%respectively. After that, with the increased depth of the cutting, the reduce scale is small.With the increased depth of the cutting seam, the position of the peak stress for the coal pillar and the distance of the mining roadway wall reduce in a way of negative exponent. The distance to the back of working face decreases in a way of negative logarithm and the average stress for the coal pillar reduces in a way of negative logarithm.(4) On the overlaying strata of the coal pillar, with the increased depth of the cut seam, the peak stress gradually reduces. When the strata horizon is lower, the peak stress is greater. The gaof strata which is near to the edge of the cutting seam, the stress gradually increases. When the rock layer is higher, the stress is greater. Compared with no cutting, when the depth of the cut seam is15m, the peak stress of the rock decreases to a larger extent. When it is at10m high, the peak stress is15.8MPa. When it is20m high, the peak stress is14MPa. After that the reduce scale is small. When the depth of the cut seam is up to30m, at the depth of10m, the peak stress of the rock is15MPa, and at the height of20m, the peak stress is12.98MPa. (5) According to the theoretical and the experimental study, the stress distribution is caused by fall-down of the roof on the lateral side, the calculation formula of the width of the plastic zone before and after the seam cutting is deduced based on the limit equilibrium method. It is showed that, under the geological conditions of ZhaoZhuang Coal Mine, the depth of the roof cutting seam is15m; the width of the protection coal pillar can be reduced by60%.