Theory and engineering practice of constructing “inner protection layer” for strongly prominent coal seams

Protective layer mining is the most effective technical means to prevent and control coal mine gas disaster, which is applicable to multiple coal seams (groups) with protected seams available for mining. With the influence of multiple factors such as increasing mining depth, mining intensity and more complex tectonics, the stress and gas coupling type of disaster for a single strong protrusion coal seam without protective layer has become the dominant. In order to eliminate the risk of coal and gas protrusion, the current measures such as mechanical reaming, hydraulic punching, water jet cutting and hydraulic fracturing can better improve the extraction effect, but fail to achieve uniform pressure relief, uniform penetration and eliminate stress anomalies, there are certain limitations to the elimination of protrusion. How to achieve efficient gas extraction and high-efficiency outburst elimination is the main technical bottleneck that has long curbed the safe and efficient mining of this type of coal seam. The study combined the engineering practice of “zero-distance protective layer” stratified mining and unloading pressure and increasing penetration of penetrating boreholes to enhance the extraction and eliminate outburst in prominence mine belonging to Henan Energy Group. The effect of pressure-releasing enhancement and outburst elimination was investigated by optimizing the design of penetrating boreholes, reasonably selecting the pressure releasing measures and accurately metering the amount of coal hollowed out. The effect of pressure releasing to eliminate outburst was strengthened, the uniform pressure releasing in a large area was realized, and a way of eliminating outburst by constructing a similar protective layer in the coal seam was formed. The “construction of inner protective layer technology” was proposed to achieve strong and uniform pressure relief, efficient extraction and rapid outburst elimination in coal seam. Summarizing the development history and experience of gas management technology in protruding mines represented by Henan Energy Coking Coal Company, the research on the “construction of inner protective layer technology” for single thick coal seam was carried out, the scientific connotation of “constructing inner protective layer” to eliminate outburst was explained, the mechanism of eliminating outburst was revealed, and the constructing method was formed. The effect evaluation technology of inner protective layer to eliminate outburst was developed, a technology system for eliminating outburst in the inner protective layer of a single coal seam with strongly outburst was constructed, and the related enterprise standard was formulated. The proposed concept of actively constructing the inner protective layer to eliminate outburst in a single coal seam with strongly outburst has innovated the connotation and extension of protective layer mining, and provided a more complete technical system and a more solid theoretical basis and technical means for the efficient outburst elimination in a single coal seam with strongly outburst.