Research On Mechanism Of Outburst Soft Coal Seam And Water Injection Strengthened By Loosening Blasting Technology

With the increase of mining depth and difficulty of coal resources,how to improve the permeability of coal seam and eliminate the risk of coal and gas outburst has become an important aspect of restricting the safe mining.At present,the existing researches on the prevention and control of coal and gas outburst by loose blasting and water injection into coal seam are still in the experimental study of single anti-outburst measures,and there are few studies on the field application of coupling prevention and control of coal and gas outburst between loose blasting and water injection into coal seam.Based on laboratory experiments,the effects of water content on mechanical properties of coal,gas adsorption and release characteristics and microscopic pore structure were studied.Through numerical simulation,the influence of different characteristic parameters on outburst risk in the process of coal roadway driving is studied,and the feasibility of coal seam water injection is confirmed.However,due to the small number of cracks in the coal seam,the effect of low-pressure direct water injection is not ideal,and the local stress concentration will occur in high-pressure water injection,which may induce the outburst of coal and gas.Therefore,a blasting enhanced water injection anti-outburst technology was proposed,and its anti-outburst effect on coal and gas was verified by field industrial test.The main research results and conclusions are as follows:?1?With the increase of water content,the compressive strength,elastic modulus,cohesive force and internal friction Angle of coal gradually decrease,the strain corresponding to Poisson's ratio,coefficient of firmness and compressive strength gradually increases.The plasticity of coal sample increases,brittleness is small,and loading capacity increases.?2?With the increase of water content,the adsorption constant a of the coal gradually decreases,the adsorption constant b gradually increases,the initial velocity of gas emission increases,permeability decreases,gas pressure in cracks and matrix decreases,peak stress decreases,and the position of peak stress gradually shifts to the deep.The number of microspores and mesopores in coal sample increased,some of them become mesopores with larger pore diameter,and the number of macropores was almost unchanged.?3?When water enters the coal body,due to the influence of water wedge,hydrolysis and hydration,the distance between coal particles is increased,and the van der Waals force between coal molecules is reduced.The original macro-and micro-cracks in the coal body are connected,and new pores and cracks are generated and continuously expanded,which destroys the structure of the coal body.In addition,because of the existence of water,a layer of water film will be formed on the macro-cracks and micro-pores of coal body,which can not only prevent the re-bonding between coal particles and the re-closure of new cracks,but also play a certain role in lubrication.When the water content of coal body increases gradually,the water film bonding force in coal body will decrease,until it is completely lost.?4?When driving a coal roadway in a homogeneous coal stratum,the smaller the elastic modulus of the coal seam is,the smaller the concentration peak of the leading stress of the roadway is,and the larger the displacement of the coal body in front of the roadway is,which is conducive to preventing coal and gas outburst.Although the greater the Poisson's ratio of coal seam is,the greater the peak value of the leading stress concentration in roadway is and the forward position of the peak value is,the effect is not obvious.Reducing cohesion and internal friction Angle of coal seam can slightly increase the stress concentration peak,but it can effectively push the stress concentration peak to the distance,so as to eliminate the occurrence of coal and rock dynamic disasters.?5?In the 8^th coal mine in the Pingdingshan coal field,a field industrial test was carried out.The effective influence radius of loose blasting was determined to be7m.In the process of coal roadway tunneling,the water content and outburst risk of coal seam are measured.The water content of coal seam is significantly increased,and the initial velocity q value and cuttings content S value of drilling borehole outburst risk index are significantly reduced.It is proved that the blasting enhanced water injection technology has remarkable effect on preventing and controlling gas outburst accidents.The research results of this paper have important guiding significance for understanding the mechanism of water content on coal mechanical properties,gas adsorption and emission characteristics,enhancing coal permeability and preventing coal and gas outburst.