The fracture mechanism and acoustic emission analysis of hard roof: a physical modeling study

Roof fracture has been a persistent threat to coal mine safety. In this paper, a physical modeling system was established to explore the fracture mechanism of the hard roof. The characteristics of acoustic emission (AE) signals during the process of hard roof failure were also studied. Results indicate that shear failure first occurs in the two ends of the hard roof beam due to the comprehensive effect of ground stress and mining-induced stress. After this failure occurs, the bending moment moves quickly toward the middle of the beam. This movement will cause tensile failure in the middle part of the beam. Broadband frequency signals are produced when a hard roof is fractured. When compared with AE energy, the AE count shows an increasing trend during a short period before each hard roof fracture. AE signals, especially for AE energy, increase steeply, reaching a peak value at the moment rock fracture occurs. These signals then drop rapidly, ending with a weak level until the next turn. Both the periodic characteristics and evolution process of AE signals can reflect not only the stress state but also the damage degree of the roof strata. These results could offer some thoughts and reference for forecasting and monitoring rock bursts caused by hard roof failure.