Based On Field Test To Research Variation Regularity Of Gas Pressure And Content In Mining Under Protection Layer

In this paper, have studied on effection of mining the under protection layer. Study on the change of pressure, amount of expansion, permeability coefficient, borehole gas flow, gas content.The maximum original coal seam gas pressure is1.6MPa, the average value is1.16MPa. Point out mining the under protection layer, original coal seam gas pressure can reduce about0.5MPa; the permeability coefficient increase in777.1times;the permeability increased1552～135times, Maximum expansion ratio reached23.7%; The2#coal seam in the original raw coal gas is reduced41.1%,from the loss, the desorption amount, the mainly reduce the loss by analysis on residual, the relative decrease of94.6%, parsing the amount of the relative decline of1.3%,and the remaining amount of the relative decline of19.1%.Through study on the change of gas pressure in and after mining the under protection layer, verify the pressure relief is irreversible, and the effection of mining the under protection layer is irreversible. Found out the negative exponential relation formula between the flow of gas and time expansion quantity and permeability coefficient.