Gas Emission Law And Control Method In Fully-Mechanized Sublevel Caving Mining Of Extremely Thick Coal Seam

With the development and application of new technology of high production and high efficiency in mine,the mining intensity of the mine is increasing.Although the coal seam gas content is low in some fully mechanized sublevel caving face,the abnormal gas emission still exists during the production because of the large mining intensity.Therefore,it is urgent to study the law of gas emission and the control method in the extra-thick coal seam.In this paper,fully mechanized sublevel caving face in 3-5# coal seam of Tashan Coal Mine is taken as the object of study.According to the problem of abnormal gas emission during the period of the period of the fully mechanized sublevel caving face,combined with field test,numerical simulation and theoretical analysis,the gas emission in goaf and the method of gas drainage is researched.The main research results are as follows:(1)The field of gas emission in fully mechanized top coal caving mining face is studied by field test.The total gas emission of the working face during the normal mining period is 56.96 m3/min,among which the gas emission of coal wall,goaf and coal mining are accounting for 3.46%,52.65% and 43.89% of the total gas emission.During the period,the total gas emission of the working face is 79.16 m3/min,among which the gas emission of coal wall,goaf and coal mining are accounting for 4.9%,63.52%,31.58% of the total gas emission.The gas emission in the goaf accounts for the main part of the gas emission in the working face.(2)The effect of hard roof movement on the gas emission of coal and rock in front of working face is obtained by numerical simulation and laboratory test.The numerical analysis results show that the abutment pressure increase rapidly before decrease to initial stresses.And it is also confirmed that the 0~12m in front of the working face is the pressure relief area of coal seam.Through the loading and unloading experiments of coal samples,the process of abutment pressure change is simulated.It is concluded that the abutment pressure will lead to the deformation and damage of coal in the pressure relief area,and the permeability of coal increases obviously from 0.087×10-3?m2 to 2.25×10-3?m2,which provides the basis for gas drainage in pressure relief area,caused a large amount of gas emission from coal seam.(3)The effect of hard roof motion on the gas emission in goaf is obtained by theoretical calculation and field test.Based on the “O-X” type breaking of hard roof,the impact process of hard roof breaking to the goaf is analyzed from the view of energy to get the relationship between the axial force of broken block and the broken expand coefficient of caving coal-rock in goaf.Besides,combined with the effect of the top-coal recovery rate and the broken expand coefficient of caving coal-rock on the volume change of goaf during hard roof breaking,the formula for gas emission increase in goaf during periodic weighting is established,and its results are compared with measured data.The result shows that the volume of goaf is reduced by the breaking of hard roof in fully-mechanized sublevel caving mining of extremely thick coal seam,so the high concentration of gas in goaf will be poured into to the working face which leads to abnormal gas emission during the periodic weighting.The theoretical calculation of gas emission increase in goaf for the 8214 working face of Tashan Mine is 14.5m3/min,and the error is between 1.79%~8.83% compared with the measured data.The results are consistent,which verifies the correctness of the formula.(4)This paper puts forward the cooperative gas drainage technology" which is suitable for fully mechanized top coal caving face in extremely thick coal seam.Based on the gas drainage of ground drilling,coal seam pressure relief area and the upper corner,put forward the cooperative gas drainage technology.The cooperative gas drainage system is established in the 8204 fully-mechanized sublevel caving mining face in Tashan Mine.After the operation of this system,the gas concentration is controlled at about 0.3% in the upper corner and the tail of hydraulic support,and is controlled at about 0.25% in return airway.The drainage effect is obvious and the hidden danger of gas in working face is greatly reduced.