Fall of ground has been considered to be the most common problematic issue faced by underground mining in decades. This elusive challenge has resulted in an increase in injuries as well as fatalities within underground mining working places (Eisner & Leger, 1988; Leger, 1991; Mark & Iannacchione, 2000; Roberts, et al., 2001; Koldas, 2001; Gumede & Stacey, 2007; Vorster & Franklin, 2008; Ferreira & Minova, 2012). Indeed, there has been a gradual rededication in accidents associated with falls of ground (FOG) from the early 90s to date (Anon, 2020). It is anticipated that this gradual reduction in FOG incidents is rejuvenated by advanced technology within the mining industry (Stacey & Gumede, 2007; Maiti & Khanzode, 2009; Mark, et al., 2011; Teleka, et al., 2012). Furthermore, FOG management is a continuous assessment wherein rock engineering specialists are brought together to come up with solutions regarding FOG. Ryder & Jager (2002) described a rock as a complex engineering material of which its behaviour is influenced by numerous factors. The environment in which the mining takes place cannot be changed (Yilmaz, 2015) as a result, the stability of underground excavations is a key concern. The focus is mainly on stability enhancement by means of excavation support designs and monitoring of ground conditions. Mining activities such as drilling, and blasting change the stress environment in the periphery of the excavation. Owing to these changes, risk assessments and close monitoring of the exposed rock mass are considered to be essential (Walke & Yerpude, 2015).
The term fall of ground (FOG) is used to classify incidents related to unexpected rock mass movement or the uncontrolled release of rock in excavations due to gravity, pressure, or rockburst. There are numerous ground monitoring systems used to manage falls of ground in the mining industry. The depth of mining has a degree of influence on the choice of fall of ground monitoring and management system approach. Deep level mines are prone to seismicity and rockburst due to high stresses, as opposed to shallow mining environments which are prone to falls of ground and minimal stresses (ISRM, 1978; Jager & Ryder, 1999; Ryder & Jager, 2002). According to Ozbay et al., (1995), shallow hard rock mining environments are usually associated with joints and bedding planes that weaken the hanging wall strata. The hanging wall rock mass at this depth is characterized by well-defined discontinuities subjected to deadweight tension (Ozbay et al., 1995). The occurrence of planes of weakness in the hanging wall strata is a major factor for excavation stability in underground mining environments (Adoko, et al., 2017). This is because the interaction of these planes may result in unstable blocks of rocks with the potential to fall under the influence of gravity. Therefore, deep level ground monitoring and management systems will lean towards seismicity, and shallow mining ground monitoring and management systems will lean towards structural analysis (Parkasiewicz, et al., 2017; Mishra, et al., 2017; Xia, et al., 2018; Malinowska, et al., 2019; Yang, et al., 2019; Rahimi, et al., 2020; Mondal, et al., 2020; Małkowski, et al., 2020). An ideal fall of ground management system incorporates visual observations, the use of ground monitoring equipment with the capability to give warning and identify structures with the potential to cause damage at an early stage. The above-mentioned combination is critical for support design and decision-making.
Fall of ground management is critical for excavation stability enhancement. The larger the excavation, the more the geological structures are exposed, which consequently influence the stability of mine excavations and the support system required thereof. The above discussion can be crystallized by an example from a study by Chikande & Zvarivadza (2016), where a platinum room and pillar mine with intense faulting and jointing of the rock mass, resulted in poor ground conditions. At times, poor ground conditions may necessitate a different mining layout as a way of managing and preventing FOGs. To enhance stability in this example, a different layout was designed for that specific ground condition, wherein two-pillar sizes were designed which are 10m x 3m and 3m x 3m, maintaining a 6m board width. Besides, a new support system was also designed for this area to help improve safety and production, as the previous support system was not adequate for such poor ground conditions. The new system included the use of longer roof bolts (2.1m) spaced at 1.2m x 1.2m whereas the previous support system had 1.8m long roof bolts spaced at 1m x1m (Chikande & Zvarivadza, 2016). Other examples of fall of ground management strategies are evident in studies by scholars cuch as Joughin (2008); Vogt, et al., (2010); Joughin, et al., (2012); Esterhuizen (2014); Joughin, et al., (2016); Chikande & Zvarivadza (2018).
In mining, rockfall-related hazards are forever present. The fact that falls of ground management strategies have been put in place means that fall of ground is a major concern. Fall of ground management is an important aspect in mining; hence, it is critical for a mine to implement a strategy that will help combat rock fall-related hazards. This study is conducted to identify loopholes within the current fall of the ground management system at a shallow chrome mine. The study helps to improve the current system, and consequently, combat falls of ground at the mine. The study focuses firstly on determining the mode of rock failure attributing to geological structures present in the mining environment. Secondly, the study helps to design an empirical support system based on a probabilistic approach using numerical modeling software packages.