The optimisation and comparison of re-entry assessment methodologies for use in seismically active mines

Abstract

The hazard posed from large seismic events is often high enough to warrant the exclusion or evacuation of personnel from underground workings. A period of exclusion is often determined following blasts or large events due to the increased risk. The period of exclusion until re-entry occurs is a decision for site geotechnical engineers and mine management that must balance the potential risk to personnel with lost production time and associated costs. There is currently no widely accepted method for determining re-entry times and mine sites typically develop their own rules for exclusions after blasts and large events. A systematic and evidence based approach to the development of re-entry protocols could potentially reduce the risk to personnel from an early re-entry or reduce the lost production from an unnecessary exclusion. Four methods of re-entry assessment have been considered in this paper. The seismic responses at three mines have been modelled and used to optimise each assessment method and gauge the relative success through back-analysis. These same techniques are available for other mines to review their own data and potentially improve their current re-entry protocols. The results of this research indicate that a real-time re-entry assessment method can offer improved outcomes compared to blanket re-entry rules by reducing the average exclusion time while still capturing the same number of large events. The incorporation of event size in the assessment can result in better results than the event count. Vallejos and McKinnon (2009) developed a probabilistic framework for re-entry assessment but this method was found to be less efficient than the blanket rule in the majority of cases in this study. The method would also result in more administration and uncertainty for mine planning and scheduling. Several potential improvements to the analysis techniques, and avenues for further research, have been discussed.

Seismic exclusions and re-entry from a risk perspective

“…The success was also quantified with respect to the average length of exclusion. Figure 9 shows the results of a systematic back-analysis of three real-time re-entry assessment methods by Tierney and Morkel (2017). The Vallejos and McKinnon method was back-analysed using the approach described by Morkel and Rossi-Rivera (2017) and a database of short-term seismic responses modelled temporally with the MOL (Woodward & Wesseloo 2015;Woodward et al 2017Woodward et al , 2018.…”

“…The analysis by Tierney and Morkel (2017) is a good example of how the effect of specific exposure management procedures can be quantified. In this case, the analysis was limited to consider different forms of re-entry analysis.…”

Seismic event location uncertainty in mining with reference to caving

“…• Re-entry after blasting/firing or the occurrence of large events (Morkel & Rossi-Rivera 2017;Tierney & Morkel 2017).…”

Numerical Modeling of Complex Stress State in a Fault Damage Zone and Its Implication on Near‐Fault Seismic Activity

“…Induced seismicity taking place in deep underground mines has been intensively studied over the past decades (Beer et al., 2017; Bischoff et al., 2010; Castro et al., 2009; Fritschen, 2010; Gay, 1983; Hofmann & Scheepers, 2011; Holub, 1996; Lasocki & Olszewska, 2017; Leptokaropoulos et al., 2017; Lu et al., 2018, 2019; Ma et al., 2018b; Malek et al., 2008; McGarr, 2001; Mikula, 2002; Ortlepp, 1992; Pritchard & Hedley, 1993; Sainoki & Mitri, 2014a; Snelling et al., 2013; Swanson, 1992; Trifu & Urbancic, 1996; Urbancic & Trifu, 1998; White & Whyatt, 1999) as it is deeply related to the occurrence of rockbursts that could inflict devastating damage to underground facilities (Blake & Hedley, 2003; Directorate, 1996; Durrheim et al., 1998; Hedley, 1992; Holub et al., 2011; Ledwaba & Scheepers, 2012; Manouchehrian & Cai, 2018; Morissette et al., 2017; Pritchard & Hedley, 1993; White et al., 2002), although not all seismic events cause violent rock mass failure entailing rock ejection with high velocity. Importantly, the location, frequency, and source parameters of seismic events provide mining engineers with valuable information (J. P. Liu, et al., 2019; Ma et al., 2018a; Tierney & Morkel, 2017; Wang et al., 2019). For instance, this includes the in‐situ stress level (Konicek & Waclawik, 2018; Kozłowska & Orlecka‐Sikora, 2017; Ma et al., 2016), its orientation (Ma et al., 2019b; Mahdevari et al., 2016), burst proneness of rock, the evolution of mining‐induced stress re‐distribution (Abolfazlzadeh & Hudyma, 2016; Beer et al., 2017; Pariseau & McCarterr, 2017), potential for the occurrence of seismic events with large magnitudes (Ma et al.,…”

“…Hedley, 1992;Holub et al, 2011;Ledwaba & Scheepers, 2012;Manouchehrian & Cai, 2018;Morissette et al, 2017;Pritchard & Hedley, 1993;White et al, 2002), although not all seismic events cause violent rock mass failure entailing rock ejection with high velocity. Importantly, the location, frequency, and source parameters of seismic events provide mining engineers with valuable information (J. P. Liu, et al, 2019;Ma et al, 2018a;Tierney & Morkel, 2017;Wang et al, 2019). For instance, this includes the in-situ stress level (Konicek & Waclawik, 2018;Kozłowska & Orlecka-Sikora, 2017;Ma et al, 2016), its orientation (Ma et al, 2019b;Mahdevari et al, 2016), burst proneness of rock, the evolution of mining-induced stress re-distribution (Abolfazlzadeh & Hudyma, 2016;Beer et al, 2017;Pariseau & McCarterr, 2017), potential for the occurrence of seismic events with large magnitudes (Ma et al, 2018), discrimination between natural and anthropogenic seismicity (Lizurek, 2017), and so forth.…”