| Currently,95% coal resource is mined by mine working in China.The high gas and gas outburst mines are accounted for more than 40% of the total national coal mine.The gas outburst coal seam is mined with rich gas content,high gas pressure,complex geological structure,undeveloped cracks,and poor permeability.The exploitation of this kind of coal seam is vulnerable to gas accident.With the increasing mining intensity and the extension speed,the mining depth is increasing.The crustal stress of coal mining is raising and the gas permeability is reducing in the exploiting coal seam,which significantly increases the danger and complexity of the gas disaster.Gas coal mine turns to high gas coal mine,while the high gas mine turns to the outburst mine.This article focuses on the outburst coal seam gas with low permeability.According to the advantages and disadvantages of our existing antireflection technology in China of the outburst coal seam,and the static expansion agent applying in the concrete demolition,rock crushing,stone cutting,engineering blasting,and rock crushing,raised a method to increase permeability and prevent outburst by using static expansive agents for cracking the outburst coal seam.Based on the theoretical research,experimental analysis and field test,the static cracking mechanism of expansive agents increased permeability of outburst coal seam and the test result in the field of Jinjia coal mine 1235 transportation roadway is studied.The main research contents and results are as follows:1)Static expansion agent hydrated with water,which gradually increased the expansion pressure and formed radial stress and tangential stress in rock mass.When the stress value is greater than the tensile strength of rock mass,rock mass will experience a crack appearing,crack propagation and crack extension.The gas permeability coefficient increased obviously after the experimental rock was swelling and cracking,according to the relationship between the gas permeability of rock mass and rock fracture.2)The operation temperature,the diameter of drilling hole,the expansion agent concentration of static influence performance of expansive agents.Under the environment of underground working,four types of static force generated by the expansion agent can reach 30-50 Mpa.By the rational layout of the free surface,the static expansion agent can all expand and crack rock mass of coal mine.3)Experiments show that: the diameter of drilling hole,the free surface,and the drilling hole arrangement influence the cracking effect of static cracking agent working on the outburst coal.During the experimental in cement tank,model of outburst coal all occurred through three distinct change process: crack appearing,crack propagation and crack extension.4)After the model of outburst coal in the cement tank experiment expanded twice,a large number of cross hole formed between the radial fracture networks.Comparing experiment scheme with the same hole diameter,the splitting effect of scheme III is the best.It is concluded that: the permeability of outburst coal will significantly increase,and the static expansion cracks AR technology is very conducive to the prevention of outburst.5)M3 outburst seam is cracked by static expansion.Through the drilling snooping instrument,it can be observed that the coal fracture in the drainage borehole was significantly increased.6)The field test has proved that: compared with the existing drainage schemes of Jinjia coal mine transportation roadway 1235,after the antireflective of the static expansion in M3 outburst seam,gas discharge and gas drainage concentration are obviously improved of the 3 different diameter gas drainage borehole.When the drilling hole diameter is 94 mm,the expansion holes and the drainage hole spacing is 12~15 times,the gas drainage effect is the best.By the scheme of drilling,the highest gas flow is up to 3.11 times,and the gas concentration is increased by 3.29 times. |
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