Study On The Mechanism Of Enhancing Permeability Of High Stressed And Low Permeable Coal Seam In Deep Mining By Pre-splitting Controlled Blasting Technology

Most of the coal seams in China are deeply buried which possessdistinctive features, such as abundant gas content with high pressure, weakstiffness, low permeability and so on. Along with the increasing energydemand and the decreasing coal reserves in shallow depth, it is undoubtly thedeep buried coal will be mined in the near future years. For the mining depthincreasing at8-12m/year, most of the coal mines will be mined at more than1000m depth during few years in our country. There are two main seriourspartential problems in deep mining which influence the safety production ofcoal mining. One is the gas outburst. Because the geostress and coal seam gaspressure are increasing with the buried depth, the strength and frequency of theoutbursts are extremely higher compared with the coal seam buried at shallowdepth. Another one is coal outburst. Therefore, the improvement of coal seampermeability is the key point to prevent outburst in mining deeply buried coalseam with low permeability and high gas pressure.The long-hole pre-splitting controlled blasting technology was presentedseveral years ago to enhance the permeability of low permeable coal seam andmeanwhile its criterion was also published in2007. Although the betterapplicability of the blasting method was gained in enhancing the coal seampermeability buried at medium depth and shallow depth, it is still deserve tostudy its effectiveness in improving the permeability of deeply buried coalseam. On the basis of previous research results, the mechanism andapplicability of long-hole pre-splitting controlled blasting method in enhancingpermeability of low permeable coal seam buried at depth are deeply studied bytheoretical analysis, laboratory model test, numerical simulation and practicalapplication.Main research works invlud as following:1,Analyzing the related influenced factors on improving the permeabilityof high stressed and low permeable coal seam buried at depth by long-holepre-splitting controlled blasting method.The related influenced factors are determined by analyzing the researchresults of former studies and considering the features of high stressed coalseam buried at depth. The related factors include such as geostress, stiffness,gas pressure of coal seam and the attenuation of blasting wave and explosiongas in coal seam.2,Theoretical study on the mechanism of enhancing permeability of highstressed coal seam using long-hole pre-splitting controlled blasting method.Base on the theoretical analysis such as stress wave theory, coal and rockmechanics, blasting theory, fracture and damage theory, firstly, the blastingwave attenuation in layered coal seam was studied; then, the crack guiding role of control hole is analyzed; finally, an time related integration formula wasderived to calculate the blasting induced crack length. Not only all the affectedfacors described above are considered, the attenuation of blasting wave in coalseam was also considered in presented integral equation. The formula could beused to compute the distance between blast hole and control hole in practicalengineering.3,Laboratory model test of long-hole pre-splitting controlled blasting inimproving permeability of high stressed coal seam containing high pressuregas.Laboratory model test on enhancement the permeability of low permeablecoal seam by the blasting method was conducted. The relationship betweenblasting induced fracture length and related factors described above are gainedthrough laboratory model test. The research results not only provide referencefor practical design, but also could be an envidence to the theoretical analysis.4,Numerical simulation study on the mechanism and effectiveness ofenhancing permeability of high stressed low permeable coal seam containinghigh pressure gas buried at depth by long-hole pre-splitting controlled blastingmethod.Firstly, the effectiveness of blasting wave and explosion gas on theimprovement of permeability of high stress low permeable coal seam werequatitatively studied respectively, by comparing the crack length sepatatelyinduced by them. Then, the permeablility improvement influenced by therelated factors presented above was studied by considering therotical analysis,labarotory test and numerical simulation results together. After that, theenhancing permeability mechanism of long-hole pre-splitting controlledblasting method was revealed. Finally, the difference of mechanism betweenlong-hole blasting and shallow blasting was presented by comparing thebehavior of blasting wave and explosion gas during the two blastingprocedures.5,Practical engineering application of long-hole pre-splitting controlledblast in improvement the permeability of high stressed coal seam buried atdepth.The long-hole pre-splitting controlled blasting techonology was improved.It included hole-sealing equipment and charging cylinder. A new drilling headwas also developed adapting to the deep coal mining. Two practical deepburied coal seam projects illustrated that the long-hole pre-splitting controlledblasting technology could be used to enhance the permeability of lowpermeable coal seam in deep coal mining and desirable effectiveness could beexpected.