An exploration of improving stability of gob-side entry retained with graded and zoned pressure relief technology: a case study

To address the issues of uncertain pressure relief effectiveness and poor control of surrounding rock caused by the composite nature of the roof strata in the gob-side entry retained (GER), as well as significant changes in strata's thickness and stability differences, this study focuses on the airway of the panel 3113 N in Longtan Coal Mine. Through field detection, theoretical analysis, and on-site applications, a stable mechanical model of the hard roof strata is established, elucidating the factors influencing fracture and instability in composite roof strata. The results indicate that roof stability of the GER depends on the position and ultimate load-bearing capacity of the hard roof strata, which in turn affects roof pressure relief effectiveness. Based on this, a roof classification method centered on "hard rock strata position and bearing capacity" is proposed. The retained roadway roof is categorized into four levels: Grade I (stable), Grade II (moderately stable), Grade III (unstable), and Grade IV (extremely unstable). Specific pressure relief methods, key parameters, roof control measures, and slope reinforcement methods are provided for each level of roof, forming a graded and zoned pressure relief technology for GER with composite roof. This approach emphasizes strong support and roof control, reinforced roadway sides, and precise roof cracking as core strategies. Field application results demonstrate that this graded and zoned pressure relief technology performs well, effectively maintaining stability of the surrounding rock in retained roadways.