Study on formation mechanism of gas flow active area in upper corner of fully-machanized mining face

In order to solve the gas overlimit problem in the upper corner during the mining process of the fully-mechanized coal mining face, with the major coal mining face in a high gassy mine in Shanxi as the model, based on the physical similar simulation test, a fractal theory was applied to prove the existence of the gas flow active area from a view of mesoscopic point. A space model and a mechanics model of the gas flow active area established were applied to study the formation mechanism of the gas flow active area at the upper corner of the coal mining face,and in combination with the FLUENT numerical simulation software, an optimization was conducted on the layout parameters of the gas drainage with the pipe buried at the upper corner. The result showed that with the comparison on the fractal features between the crack network of the local gas dominant channel and the crack network of the integrated overburden strata, the development of the local crack network considered was abundant and the existence of the gas flow active area was proved. The second unstable mode and criteria of the key rock block in the gas flow active area were deduced. The paper held that the key rock block with no second unstability occurred could ensure the existence of the key rock block, thus could ensure the gas flow active area without a disappearance occurred and could prove a stable reference location base to the gas in the gas drainage area with the pipe buried in the upper corner. When the pipe buried depth was 5 m, 15 m and 25 m, a numerical simulation was conducted on the gas concentrations distribution in the goaf and the coal mining face. The paper held that the gas drainage effect was the best when the pipe buried depth was 15 m.