Field experiment on directional roof presplitting for pressure relief of retained roadways

Roadway failure control in modern longwall mining has been universally difficult and needs to be resolved. To address the failure of retained roadways in longwall mining, in this study, a novel approach of directional roof presplitting (DRP) is introduced and examined through a field experiment. The DRP method utilizes the mine pressure effect and broken expansion nature of rock to achieve the active pressure relief of retained roadways. Directional tensile blasting presplits the trial roadway roof by forming a smooth fracture surface in the roof. After mining, the gob roof within the presplitting height caves in under the mine pressure and subsequently expands to fill the gob to counter the mine pressure. A field test was conducted, and a comprehensive monitoring scheme and a system were designed to study the DRP effect. The results indicated that, the trial roadway roof can be directionally cut apart under the guidance of the charge test and with the help of the established theoretical model for hole distance; after blasting, the roof could maintain its reliability, even though the working face approached. After mining, the retained roadway with DRP exhibited good pressure relief. Roof integrity was guaranteed; furthermore, roadway convergence significantly decreased, and sidewall stability on the pillar side was improved because the high pressure transferred to a farther position. In addition, DRP reduced the scope and degree of the lead abutment pressure and the periodic weighting loads on the working face. This study provides an effective and practical way to control retained roadways and potentially discusses a new approach for utilizing the geomechanical characteristics to prevent and control the mine pressure disasters.