PHYSICS OF ROCKS AND PROCESSES

The gradual depletion of the natural resources has led to the extraction of precious metal at a great depth ranging from 1.6 km to 4.0 km from the earth surface. As a result most the South African Gold Mines are currently operating at a great depth in order to extract gold deposit. However, this great depth comes with several challenges that cannot be solving using traditional, conventional and numerical simulation. According to the annual accident statistics released by the Department of Mineral Resources [1] in South Africa, extensive contribution of fatalities in South African Gold Mines have resulted from rock related incidents. Although there is a rapid drop on rock related fatalities from 1950s to present (2018 to 2019), but the rock related fatalities are still reported at an alarmic rate. Nevertheless, majority of these events were noted to be related to so-called Rockburst. There has been several arguments concerning the actual definition of the so-called Rockburst, in which Kaiser et al. [2] defined it as a damage that took place at the vicinity of the excavations; this damage was indicated to occur in a sudden and violent manner which is associated with seismic events. However the damage can differ based properties the rock mass and properties of the seismic events, as well stresses revolving around the excavation. The definition has been supported or validated by several studies which includes; Cai and Kaiser [3], however Ortlepp [4] provided a slightly different approach, in which the author defined so-called Rockburst as seismic event that generate a violent and substantial damage at the vicinity of the mine excavation. Cai and Kaiser [3] contested that rockburst is understood to be allied with “damage to the excavation or its support system”, the authors further the argument by indicating that “seismic event alone without causing damage is not rockburst”. For argument sake, it is very complex to argue that the so-called Rockburst is simple defined as a damage to the excavation or its support only, suppose there is a Fall of Ground (FOG) due to gravity or disintegration of the wedge/s on the hangingwall, the excavation and support damages are still experienced, therefore, the question will be is that still called rockburst based on the suggestion or proposal by Cai and Kaiser? This study proposed that a rockburst can be simply defined as the sudden release of energy (seismic event) from the rockmass which damages the excavation or its support system (term support system is referred to both reinforcement and support system in this study). Additionally to the previous discussion, Ortlepp and Stacey [5] provided five classes of rockburst noted in South African Gold mines which includes; Strainburst, Buckling, Pillar or face crush, Shear rupture and Fault-slip. All this classes has been evidence in several recent studies [6] and are still considered to be a problematic issue faced by South African deep to ultra-deep gold mines. Brummer [7] stated that preconditioning appears to be a viable technique for combating the “crush” type rockbursts and has been shown to be successful worldwide, in hard rock and coal mines. The conclusions made by the previous has correspond very well with the outcome from Ryder et al. [8] in which the authors commented that preconditioning is one of the major strategies for dealing with the rockburst hazard and they described it as an active engineering measure to modify or control the dynamic behaviour of the rock. The preconditioning research has attracted many scholars due to continuous reporting of rock related issue from the mining houses in South Africa. In supporting the previous statement, Toper [9] has conducted a study on “the effect of blasting on the rockmass for designing the most effective preconditioning blasts in deep-level gold mines”, the author proposed that the preconditioning technique is a rockburst control technique which is intended to alleviate the effects of potentially damaging seismic events on the excavation face areas, with special reference to face ejection type of rock bursts. Owing that, the previous author also commented that the practical difficulties and the cost are probably the main reasons that preconditioning is not used extensively in South African mines [9]. In principle, the preconditioning technique is intended to prevent the accumulation of strain energy ahead of the working face or, at least control the release of the strain energy. The gas UDK 622.83