Regional Outburst-prevention Technique by Gas Pre-drainage Based on Large Diameter Boreholes along Coal Seams under Deep Mining

摘要

This paper presents the procedures and effects of strip pre-drainage of coal seam gas by long boreholes with large diameter. The investigation was carried out by onsite experimental measurements and laboratory numerical modeling. Onsite investigation results from the six roadways of Dingji Mine show that the technology has dramatic effects of stress release and gas pre-drainage. For a single borehole, its effective influential radius reaches 2.3m after five day drainage, with pre-drainage rate over 30%, residual gas contents ranging from 2.34~4.53m~3/t, coal seam deformation over 1.1%. Boreholes were drilled according to a refined pattern of boreholes based on these parameters, which has highly increased the rate of roadway development to over 170m per month and the maximum to 212m per month. Of all routine inspections, only 5.38% indicates some degree of outburst potential after this technique is applied. The majority of inspections with outburst potential are limited to locations where abnormal disturbance occurs because of geological structures, indicating enhanced and intensified borehole drilling is necessary when development is close to geological structures.