Study On Overburden Mining Effect And Roof Water Disaster Prediction In Multi-seam Mining

The coal mining has been in existence for more than 100 years in our country.With the development of economic level,the demand for coal is increasing year by year.Coal seams with simple mining conditions will be exhausted.With the increase of mining depth,the phenomenon of multi-seam mining is becoming more and more common.However,due to the influence of interlayer lithology combination,interlayer spacing and mining production conditions,multi-seam mining has caused many mining problems,such as roof separation water hazard,secondary roof breakage and strong rock pressure,which threaten the safety of coal mine production.The failure mechanism of roof overburden is studied,based on the superimposed mining of 8 coal,6^-3 coal and 3 coal in Wulunshan Coal Mine and combined with the water inrush from the working face of8 coal and 6^-3 coal.Through field investigation,theoretical analysis and numerical simulation,the focus is on the separation position,breaking distance and the height of the water-conducting fracture zone of 1601 working face of 6^-3 coal,and the dangerous zoning of water inrush in mining area is analyzed based on borehole data of a mining area.?1?Through the drilling data of exploration and reconnaissance of Wulunshan Coal Mine,the distribution characteristics of each coal seam and interlayer lithology combination are studied.The analysis shows that the spatial occurrence of 8 coal and 3 coal in a mining area has little change and is relatively stable.6^-3 coal thickness changes greatly.The lithological assemblages of coal seam roof are fine sandstone,siltstone,mudstone,coal and limestone interbedded,but the lithological proportions are different.8 coal roof is mainly composed of fine sandstone and siltstone,6^-3 coal roof is mainly composed of siltstone,mudstone and fine sandstone,and 3 coal roof is mainly composed of siltstone and mudstone.?2?Through the analysis of the water inrush from the 1601 working face,it is determined that the direct water-filled water source of the 1601 working face is the sandstone fissure water in the upper part of the Longtan Formation?P₃l³?,and the indirect water-filling source is the Changxing Formation and Dalong Formation?P₃c+d?.Then by theoretical calculation,based on the key position of the key strata theory layer 1601 face the preliminary determination,in conjunction with analysis projecting face water source,the primary key to determine the initial layer 1601 at the sandstone of the bottom face floor 3 coal,and the separation space may be formed near the key stratum position.Based on the plate theory and the calculation of the breaking distance of the working face,combined with the position of the working face when the 1601 working face bursts,it is expected that the 1601 working surface cycle breaking distance is 68m,and the 1603 working surface cycle breaking distance is 73m.Based on the comprehensive empirical formula and the prediction of the height of the water-conducting fracture zone based on the key layer position,it is preliminarily estimated that the development height of the water-conducting fracture zone after the mining of 1601 working face is 39.8m.?3?Through the discrete element 3DEC software,the overburden fracture of the working face is simulated.After the mining of the lower 8 coal working face,separation layers are formed near fine sandstone,argillaceous siltstone,limestone and argillaceous siltstone in the upper 5^-3 coal roof of Longtan Formation 42 m away from the roof of the 8 coal seam.During the advancing process of 1601 working face,the separation space formed in the earlier mining face is gradually compacted,and the advancing end of the working face.The separation layer develops in the limestone,argillaceous siltstone and fine sandstone of Longtan Formation,which is consistent with the theoretical calculation.During the advancing process of 1601 working face,the separation space formed in the earlier mining face is gradually compacted,and the advancing end of the working face.The separation layer develops in the limestone,argillaceous siltstone and fine sandstone of Longtan Formation,which is consistent with the theoretical calculation.?4?According to the actual water inflow of 1601 working face,combined with"virtual large diameter well"method,the comparison method and the consideration of the amount of water inflow under the condition of uniform discharge of the separated layer,the normal water inflow of1603 working face is estimated to be 46-57.5 m³/h without considering the normal water inflow of separated layer.When considering the uniform discharge of separated water,the normal water inflow is estimated to be 64-75.5 m³/h;and the maximum water inflow is about 265 m³/h.?5?Using analytic hierarchy process?AHP?,the risk zoning of water inrush in a mining area is divided into seven evaluation indexes:6^-3 coal thickness>the height of water flowing fracture>depth of 6^-3 coal roof to K2 limestone>aquifer thickness>mudstone thickness ratio protective layer thickness?distance between the highest conductive height and K2 limestone?.The positive correlation index are:6^-3 coal thickness,the height of water flowing fracture,the thickness of the8 coal and the thickness of the aquifer,and the negative correlation index are:6^-3 coal The height from the roof to the K2 limestone layer,the ratio of the thickness of the protective layer to the thickness of the mudstone.The results are as follows:the north boundary of the mining area is in dangerous area,the angle between the south boundary and the west boundary and the middle part of the east boundary are relatively safe areas,and the rest are in relative dangerous area.