Analysis on Gas Flow Attenuation Features from Borehole Along Soft and Unstable Seam

In order to obtain the gas limit drainage value of the borehole along the soft and unstable seam and the influence scope, based on the gas flow attenuati on features from a single borehole under the high negative pressure continued gas drainage conditions, the borehole gas parameters were measured and the gas flow and concentration attenuation curves was drawn. The gas flow theory and the rock and soil mechanics related theory were applied to comprehensively analyze the gas f low attenuation law of the boreholes. The results showed that under the sustained high negative pressure drainage conditions, the surrounding coal mass of the borehol e along soft and unstable seam would finally form a loop region from different developed cracks to outward expansion. The gas flow and concentration variety of the bor ehole would have three stages, including a rapid attenuation stage, unstable rising and dropping stage and limit drainage stage. Finally the gas drainage values and infl uence radius at different attenuation stage were calculated, the effective influence radius of the borehole was 1. 55 m and the gas drainage period was 33 days.