Determination Method for Borehole Bottom Location of Pressure-relief Gas Extraction Boreholes

To master the height of the fractured zone and to arrange drainage borehole's bottom location are the key to improve the effect of the pressure-relief gas extraction. Aiming at the geological conditions of the Liyazhuang Mine 2-603 working face, the reasonable drainage borehole's bottom location was determined by the method of theoretical calculation, numerical simulation and drilling extraction test. Firstly, the average height of the fractured zone was 32.8 m to 44 m by the theoretical calculation. Secondly, the numerical simulation analysis showed that the fractured zone was at the height of 13 m to 25 m, 38.6 m to 50 m to the floor, and in the rise-entry mining angle of 62°. Finally, in the high level gas drainage roadway, six drainage boreholes were arranged in the different layers of the fractured zone. The reasonable location of the borehole bottom was at the height of 44 m to the roof based on the gas extraction effect of the borehole. The method can be applied in the similar geological conditions.