Application Research On Gas Migration Mechanism And Control Technology Of Fully-mechanized Top Coal Caving Mining

Gas accumulationmay easily occurred in some parts of fully mechanized caving face because of the high gas content in the coal seam, the high mining intensity and the great amounts of residual coal in goaf. This can result in accidents such as gas explosion, gas suffocation and so on. To solve this problem, N2015 working face of Tunliu coal mine is selected as the research base.Some methods, containing theoretical analysis, numerical simulation, similar experimentand field application, are combined together to study the gas migration mechanism in the gas pre-drainage coal seam, the goaf and the working face, and additionally to analyze factors causing gas accumulation in fully mechanized caving face. Besides, a comprehensive project about gas pre-drainage in coal seam, drilling in the fractured zone of goaf, the intubation extraction of gas in the upper corner and mining technology parameters is developed, and finally applied in the field practice.According to the theory of seepage in porous medium, numerical models including the gas desorption-diffusion model in pre-drainage coal seam, the gas migration model in goaf and the gas diffusion model in the whole working area of the fully mechanized caving face are established respectively. All of these models are effectively solved by given the boundary and initial conditions. They provide a theoretical basis for the numerical simulationsand similar experiments, and also lay the foundation for studying factorscausing gas accumulation.Based on the practical situation of N2015 working face inTunliu coal mine, geometric modelsincluding the gas desorption-diffusion model in pre-drainage coal seam, the gas migration model in goaf and the gas diffusion model in the whole working area of the fully mechanized caving face are established.Numerical simulations are conducted with the boundary and initial conditions. The result shows that the range influenced by permeability of gas pre-drainagecoal seamand original gas pressureis 1.0～1.7m and 0.4～0.6m, respectively, and the range influenced by the drillingdiameter is 6-7 times of the diameter. Moreover, the "U+L" or "U+I" ventilation type is more effective for reducing the concentration of gas in goaf and decreasing the amount of gas flowing into the working face.The "U+L" ventilation type is finally adopted with thewind speed at 2.5-3.0m/s and the advancing speed at 4.8m/d to prevent gas accumulation.The necessary parameters of similarity criteria, including length of goaf(xr), particle size of filling material(dnr), seepage velocity (ur), porosity(δr), flowing pressure(pfr), temperature(Tr) and quantity of flow (qr), are derived on the basis of gas seepage equation. With an additional computation for range of the three regions in goaf, the similarity modelof the goaf is established. In this way, the law of gas flow and gas concentration distribution under different modes of ventilation and wind speed in goaf are studied, as well as the factors causing gas accumulation.By means oftheoretical analysis, numerical simulation and similar experiment, a comprehensive plan for N2105 working face is developed to government the drilling and pre-drainage of the coal seam, the drilling of the fractured zone andthe intubation extraction of theupper corner. Reasonable technologyparameters for mining are also well determined. Besides, the plan is successfully applied in thefield.