Research On Laminar Spallation Mechanism Of Coal And Gas Outburst Propagation

Coal and gas outburst is the unstable failure of coal containing gas under thecombined influence of stress and gas. The fracture expands and the coal is strippedand threw out into the mining space in the process of outburst. Therefore, it needs tostudy the mechanism of coal and gas outburst propagation in order to establishtheoretical basis for preventing and controlling the coal and gas outburst.The theories of Rock mechanics, Physical Chemistry, Fluid mechanics andSimilarity theory, combining the theoretical analysis and laboratory experiment wereemployed to research in this dissertation. The adsorption/desorption regularities,constitutive relations and permeability evolution of gas-saturated coal under couplingbetween stress-gas-temperature were studied. The similar experiments of coal and gasoutburst were conducted. And then the laminar spallation mechanism of outburstpropagation was studied based on the condition of experiment. There are someinnovations in the dissertation. The main conclusions are listed as below:The adsorption constant a doesn’t change with the temperature, but theadsorption constant b changes drawn from the adsorption experiment of coal samplesfrom No.10coal seam in Wolonghu coal mine. The relationship between the gasdesorption quantity from coal particle and the square root of time under the isothermalconditions complies with the form of Langmuir equation.The complete stress-strain progress and the evolution of permeability through theprogress can be simplified into four stages: Linear elastic stage (permeabilitydecrease); Nonlinear elastic-plastic stage (permeability increase); Drop brittle stage(permeability increase rapidly) and Ideal plastic stage (permeability stabilizes).Consider a cube build a physical model of the internal structure of coal fracture, onlya portion of the coal matrix swelling deformation has effects on coal fracture basingon the structural analysis of coal fracture. The impact factor of coal matrix swellingdeformationf m(0＜f m＜1) was brought forward to demonstrate the effects of coalmatrix swelling deformation on fracture. And the corresponding constitutive equationsand permeability evolution equation were established under the condition of couplingmulti-fields (stress field, gas field and temperature field).Based on the similarity criteria, a truly triaxial experiment system simulatingcoal and gas outburst was designed and manufactured. The main parameters of systemare: gas pressure≤10MPa; ground stress≤27MPa; temperature from room temperature to60℃. Similar experiments of coal and gas outburst were carried out. Based on theconditions of experiments, a laminar spallation model of outburst propagation wasestablished, in which effects of tensile fracture due to gas expanding, swelling andstrength reducing caused by sorption were solved. The influences of gas pressure,absorptivity, fracture toughness and permeability of coal on the outburst propagationwere investigated by solving the established outburst model in different conditions.The outburst is a fast dynamic process, of which the propagation time is1.68s onaverage obtained by model study. The process of outburst propagation could bedivided into three stages, which are acceleration period, stable period and decayperiod. After the trigger of outburst, the coal is rapidly destroyed by the effect of largegas pressure and its gradient. Because of the largest gas pressure gradient, thethickness of the spherical shell produced by coal breakage is small at this time. Thepressure distribution and burst velocity on the front of outburst face are basicallystable. The width of zone of gas pressure gradient is7.33cm on average and thegradient is8.215MPa/m on average. The split velocity increases from1.32m/s intime of0.4s to1.54m/s in0.9s. The propagation velocity of outburst is about0.15193m/s.The gas pressure and its gradient in the unbroken coal gradually decrease withthe outburst propagation leading the gradually increase of the coal laminationthickness. At last the outburst stops due to gas out of store.