Study on Safe Rock Pillar Thickness and gas source control with short distance protective layer extraction

Rational thickness of safe rock pillar and effective measures of controlling gas are the key to achieve safe and fast tunnel excavation in short distance protective layer. Combined with gas-geology condition in 5th Mine in Pingdingshan Tian´An Coal Mining Corporation, a numerical model of safe rock pillar thickness is established by FLAC^3D software to simulate distribution law of tensile stress and vertical displacement at the protective layer floor with different gas pressure and rock pillar thickness. Simulation results show that when safe rock pillar thickness between protective layer and protected layer is shorter than 5.0m, the protected layer will be in coal-gas outburst potential. Based on these results, the effective measures are taken to detect gas coal layer and geological structure to prevent the gas outburst of protected layer. The method of gas sources control is proposed through measuring and analyzing gas emission sources during tunnel excavation process. Field test results show that measures are safe and effective in fast driving. So the methods could be used in controlling gas outbursts under the similar conditions.