Well working is the main characteristics of coal production in china, Pre-extrtaction is an important technical measure to achieve mining of coal and gas and effectively prevent gas disaster in coal face.However,with the extension of mining depth,the distribution of soft coal seam has been expanding.As the soft coal seam is high gas content and low permeability.it has been difficult and key for the coal seam gas extraction.How to increase the permeability of coal to effectively increase gas extracti...