| In the past ten years, gas disaster has become the biggest threat in the mine disasters in our country. Gas disaster intensified caused by coal mining technology and equipment for the development of mining depth increase rapidly, now kilometers above the mine in our country has meet the eye everywhere. The increase of the mining depth increasing brings stress and the gas pressure, and decrease the permeability coefficient, leadind to the danger of the mine gas accident occurred such as the coal and gas outburst. The gas accident’s damage is great, the coal resources and the safe of life would be seriously threatened. Therefore, how to increase the permeability of the coal seam, to eliminate the risk of coal seams outburst has become an urgent problem.In this paper, through theoretical analysis, numerical simulation and method in combination with the engineering test, the application of pressure relief and permeability increasing technology in low permeability and high gas coal seam in the deep hole pre-splitting blasting was studied systematically, discusses the microscopic pore structure of low permeability coal seam, the effects of detonation wave and detonation gas, the role of control hole in blasting, combined with the simulation and field. Fianally we make the following conclusions:1. The development degree of fracture pore structure of porous media of the coal, and the porosity, permeability or other properties of coal and gas permeability are closely related, many factors will affect the porosity of coal; deep hole pre splitting blasting will be destroyed coal body in a certain range, the microscopic pore structure of coal, especially the pore structure of small holes and middle holes in the coal body will be deeply influenced,so the specific surface area and pore volume will increase, promoting the extensive development of cracks, so as to improve the coal permeability coefficient.2.By discussing deep hole pre-splitting blasting pressure relief antireflection mechanism,analyses stress wave,control hole,detonation gas and coal seam gas pressure,in the role of crack propagation.Firstly, the stress wave acts on the coal and rock,producing radial compressive stress and tangential tensile stress,makes the coal produces crack;secondly,the reflected tensile wave formed in the control hole further increases the cracked area;Finally, high-temperature,high-pressure gas and coal seam gas detonation pressure together act on the gaping fissures of the cavity walls and cracks tip stress concentration,so that further expansion cracks and eventually formed a circle and secondary fractures,including fractures circle the complex fracture network.3According to the situation of No.15mine coal roadway driving in Zhenghang, we use three-dimensional dynamic finite element program LS-DYNA3D to establish numerical models that conform to the actual conditions;Through Numerical simulation of stress cloud crack picture of a single hole blasting; a single blasting hole and two control holes (the hole spacing are respectively1.5m and3.5m),reproduction of the stress wave propagation and attenuation law in the coal and rock,and expansion in the process of coal and rock fissures;When the hole spacing keep distance of1.5-3m,can make large amounts of coal and rock through fissures, also can improve the permeability of coal seam and gas drainage effect4.From the test results in track down II of coal seam15in Zhenghang, the effect of deep hole presplitting blasting pressure relief antireflection test is obvious, significantly increases the permeability of coal, improves concentration and extraction volume of gas extraction, reduces the coal seam gas pressure and gas content.lt has been proved that this technique plays a positive role in pressure relief of high outburst coal seams of low permeability and provides a guidance for future similar process. |
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