Experimental Study Of Gas Seepage On The Protective Layer Mining Conditions

The exploitation of Protection layer is an important method to prevent the outburst of coaland gas.The purpose of exploiting protective layer is to use the law of rock motion caused bythe rock pressure, so that the protective layer can release elastic potential energy and increasethe seam permeability because of the swelling and deformation, thus gas is exploitedefficiently. This essay is based on extensive collection of theoretical document and research,use the research method of combing both theoretical analysis and similar material simulation,systematically study the change situation of gas permeability when the working surfacechanges under the conditions of different spacing and mining.The experimental study shows during the process of exploitation, the Protection layertakes different effects on pressure relief due to the different exploitation level, this makes theprotective layer swollen and deformed and the permeability rate changes in a regular way.With the different stages of working face impelling, the protective layer also experienced thefive different stages of original stress equilibrium, the stress concentration, pressure reliefexpansion, gradual compaction stage and restoring to the balance stage, making itspermeability rate also experienced a five different stages of original permeability, lesspermeability and less flow, pressure relief and high permeability high flow, the groundpressure restoring to the less permeability and less flow, and the permeability rate restoring tothe balance, so that the gas velocity speed in the rock appears the same process of firstdecrease, then increase, again decrease and unchanged finally.When the exploitation of protective layer is completed, through collecting theexperimental data and curve matching, the permeability rate change curve of protective layer takes the saddle-shaped along the strike direction. The permeability rate change weakens withthe increase of distance between protection layer and protective payer, which further explainsthe more the spacing becomes loser between the protection layer and protective payer, themore obvious of the relief effect. This provides certain theoretical basis for the optimizationof gas extraction system layout, the extraction concentration, the extraction volume and rate.