Research On Roof Pressure Control Of Close Distance Coal Seam And Spontaneous Combustion Prevention Of Goal

Considering a series of problems caused by roof structure and stress change in close coal seams such as the roof of the lower coal seam leakage,roadway surrounding rock deformation in large quantity,difficulty of support,air leakage in the working face and spontaneous combustion in goaf,this paper take Jialequan coal mine and Huayuan coal mine as an example to systematically study the stress distribution of surrounding rock,mine pressure law,reasonable position of roadway,reasonable alternate distance of working face,spontaneous combustion law and control technology of goaf through site investigation,numeral calculations,theoretical analysis and field test.The main research contents and results are as follows:(1)Based on plastic theory,the maximum failure depth of No.8 coal seam of Jialequan coal mine floor due to mining is 25.3m.Using numeral calculations,the scope range of 3 zones(stress increasing zone,stress decreasing zone and original rock stress zone)of vertical stress and horizontal stress in floor stratum can be ensured.(2)The deformation mechanism of pathway roadway in No.9 coal seam of Jialequan coal mine is revealed.The roadway is in area of stress concentration under coal pillar and affected in partial load.The mining roadway is located15 m out of coal pillar.The deformation value of mining roadway in mining this working face,adjacent working face and alternate mining increase significantly.It should strengthen the support of crossheading in forward of coal rib 20 m.(3)The pressure law and load constitution of working face in No.9 coal seam under goaf are studied.The first caving step distance is 7.8m,the first weighting step distance of basic roof is 19.8m,the periodic weighting stepdistance is 6.3m.The support is in state of high resistance,which show that the strata behaviors of No.9 coal seam is affected by the goaf and pillar in No.8 coal seam.The working resistance and setting load of support is 4500 kN per rack and 3600 kN per rack,respectively.The obvious influence zone of forward bearing stress is 30 m in front of coal wall.(4)The reasonable alternate distance of working face is studied based on theory calculation and numeral calculations.The overlay characteristics of floor stress in goaf of No.9 coal seam and bearing stress of No.10 coal seam can be obtained.The reasonable alternate distance of working face is more than 35 m.Combined with in-situ measured data,for No.9 and 10 coal seam,the first weighting step distance of basic roof is 50.8m and 23.3m,the periodic weighting step distance is 19.8m and 10.8m,and the rated working resistance is 4000 kN per rack and 6500 kN per rack.(5)The prediction model of spontaneous combustion in goaf of combined mining of contiguous seams is builded.Oxygen concentration in goaf in No.10201 working face show reverse“U” type and the area of coverage of oxygen concentration 7%~18% in injecting nitrogen is relatively larger.The range of spontaneous combustion "three zones" is divided.The integrated technology system of natural fire prevention and control in goaf such as upper and lower corner of the working face plugging,spraying inhibitor,nitrogen injection,gel anti-extinguishing system,and scheme of work face CO overrun is drawn.