Study on Pressure Released Gas Drainage in Protected Seam with High Level Borehole Under Y Type Ventilation

In order to prevent the pressure released gas of the protected seam flowed to the protective seam in a large quantity which would cause a gas content 0 ver the limit in the air returning gateway and goaf of Y type ventilation coal mining face, according to the pressure releasing theory of the protective seam mining and th e gas migration law of the crack three zone in the overburden strata above the goaf, high level boreholes set in the coal mining face with a Y type ventilation were appli ed to drain the pressure released gas from the protected seam.A design was conducted on the key parameters of the high level boreholes in the site of Yangdong Mine. The height designed of the final borehole location was 24 m, the inclination control scope designed was 9.5-60.0 m and the spacing designed of the finale boreholes wa s 10 m.The site application results showed that the gas drainage rate of the high level borehole was 60.8%, the average gas volume fraction in the air returning gatewa y kept at 0.27%，the max fraction was 0.46% and the gas content over the limit in the Y type air returning gateway and the goaf was eliminated.