Unfavourably positioned geological faults may play a major role in the occurrence of high energy release rib failures in underground coal mines, known as coal bursts. The influence of the geological fault proximity to the roadway on rib stability was investigated using numerical modelling, and stress distributions and energy changes about the fault were analysed. Findings suggest that the amount of energy released during fault-induced rib failures gradually increases as the proximity of the fault to the roadway increases. However, beyond a critical distance, the influence of faults starts to diminish and the energy release declines.

1 Introduction

The terms rock burst and strain burst are used to describe unstable rock failures involving sudden and rapid release of the stored strain energy in the system and poses one of the highest health and safety risks in underground mines and tunnels (Cai 2013, Chen et al. 1997, Dou et al. 2017, Mark 2016, Whyatt et al. 2002, Zhang et al. 2017a, Zhang et al. 2013). In a rock burst, broken material is ejected into the excavation and can cause risk to underground workforce. This operational hazard is also named coal burst in underground coal mining terminology and specifically refers to coal as the type of ejected material (Galvin 2016). A coal burst is a rock burst where the ejected material is coal.

Geological faults are accepted as one of the main sources of coal and rock burst incidents. It is commonly recognised that burst proneness increases as the mining takes place in the vicinity of such geological discontinuities (Durrheim et al. 1998, Gay 1993, Gibowicz & Kijko 2013, Hedley 1992, Jager & Ryder 1999, Jiang et al. 2010, Mark & Gauna 2016, Salamon 1983, Snelling et al. 2013, Vardar et al. 2018). Several researchers have conducted numerical simulations and parametric studies to investigate the coal and rock burst mechanisms in underground mines and tunnels, and to provide insights on the impacts of geological structures on burst occurrences. Chen et al. (2018) investigated reverse fault reactivation and stress redistribution characteristics during fault formation using 2D and 3D numerical simulations. They have also evaluated the stability of the roadway mining toward the fault and reported high vertical stress concentration regions in the footwall of the fault and excavation boundaries. Gu and Ozbay (2014) used numerical modelling to simulate mining-induced unstable slip of horizontal geological discontinuity above an advancing tabular excavation and noted significant seismically released strain energy magnitudes. Manouchehrian (2016) extensively studied the effects of weakness planes around deep tunnels and showed that such features can alter the loading system stiffness and induce unstable failures resulting in high kinetic energy and ejection velocity values. Other researchers also investigated unstable rock failures in underground excavations using numerical models (Khademian et al. 2016, Kias & Ozbay 2013, Poeck et al. 2016, Tahmasebinia et al. 2018, Zhang et al. 2017b). Although the studies available in the literature are insightful, most of them are not directly applicable to coal mining as many factors such as stress environment, rock types, mining methods and excavation geometries differ to a large extent. Furthermore, despite a significant portion of coal bursts occurring in development roadways (Mark 2016), there is still a limited quantified understanding of the influence of faults on these incidents.

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