Study on pressure relief mechanism of hydraulic support in working face under directional roof crack

When mining coal from the working face, the main roof withstands the overlying strata. The main roof’s first weighting and periodic weighting may cause accidents, such as crushing the working face hydraulic supports. A mechanical model of the main roof was constructed, and the contributing factors of first and periodic weights on the main roof were examined in order to prevent such accidents. The thickness of the main roof was found as the most contributory factor to the main roof’s stability. Therefore, a new directional roof crack (DRC) technique is proposed, which produces directional cracks in the main roof through directional blasting and makes part of it collapse in advance so as to reduce the thickness and relieve the first and periodic weighting. To verify the effectiveness of DRC, the mechanism of DRC was analysed. A mechanical model of the hydraulic support was constructed, and the DRC techniques were tested on-site. Field experiments with a complete set of monitoring schemes showed that, with DRC technology, the roof periodic weighting interval decreased by 35.36%, and the hydraulic support pressure decreased by 17.56%. The theoretical analysis was consistent with the measured results. Therefore, the DRC technology is feasible and effective to ensure mining safety at the working face.