Laboratory determination methods and applications of sensitive indicators and critical values for coal seam outburst prediction

This paper adopts a method for screening sensitive indicators for coal seam outburst and determining their critical values under laboratory conditions. Firstly, soft stratified coal samples from a certain coal mine experimental coal seam are collected. In the laboratory, the soft stratification of the experimental coal seam is replicated, and gas at different pressures is injected to form simulated coal seams with varying degrees of outburst danger. Secondly, various existing prediction indicators for coal seam working faces are measured by drilling, and the relative sensitivity and absolute sensitivity of each indicator are obtained. The prediction indicator with the highest sensitivity to coal seam outburst is quantitatively selected — the initial gas outflow volume from the borehole （Q）. Finally, based on the characteristic that the initial gas outflow volume from the borehole（Q） increases linearly with the increase of the initial released gas expansion energy （W）, the variation law of the initial gas outflow volume from the borehole （Q） at different drilling speeds is analyzed. The calculation formula for converting the initial gas outflow volume from the borehole（Q） at any drilling speed into the initial gas outflow volume from the borehole（L_z） at the standard drilling speed, as well as the critical value for outburst, is derived. Field application results show that the initial gas outflow volume from the borehole （L_z） at the standard drilling speed can change significantly with the outburst hazard of the working face of this coal seam, and it is very sensitive to outburst. Continuous measurement of the initial gas outflow volume from the borehole （L_z） at the standard drilling speed can detect at any time whether there is a coal body with outburst risk in front of the working face. This proves that this method of determining sensitive indicators and critical values for coal seam outburst through laboratory tests is feasible. The successful experiment of this method also provides a new platform and idea for outburst prediction in subsequent coal seam working faces.