ETD Collection

Permanent URI for this collectionhttps://wiredspace.wits.ac.za/handle/10539/104


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    Validation of a dynamic simulation of an opencast coal mine
    (2019) Muniappen, Kesavan
    A dynamic simulation study is a critical deliverable of a mine project feasibility study. Mining houses rely on simulation to confirm that complex, integrated systems can achieve design capacity before investment decisions are made. Dynamic simulations are powerful tools, but only if they are developed using the right methodology, and with information that has been verified. The importance of work in the field of mine dynamic simulation validation was made clear during the early stages of this research report when it was identified that there is limited information available on the subject. Work conducted in the realm of validation can make an invaluable contribution to the success of future projects undertaken around the world. The last few years have been difficult for employees of some mining companies because of looming job cuts due to high production costs, high overheads, and decreasing product demand. For many mining companies, it was a case of survival which gave rise to the development of new strategies and innovative thinking. Coal Mine A Life of Mine (LOM) extension project is a prime example of innovative thinking. In this case, the project was approved for implementation when export coal prices were on the low end of the price cycle. The dynamic simulation of the full materials handling value chain conducted during the project was of utmost importance, and provided assurance to the project review team that annual production targets can be achieved. The simulation development methodology was based on a unique approach that reduced time spent on the simulation through the integration of different, independent models that represented sub-systems in the materials handling value chain. There was, therefore, a strong need to validate the simulation, which could lead to the adoption of this approach on future projects. In this research report, the LOM extension project scope and the mining activities conducted by Coal Mine A are explained, and a brief, but interesting history of Modelling and Simulation (M&S) is provided. The subject of M&S is vast and has evolved into its own separate discipline. M&S is an invaluable tool, and the importance of verification, validation and credibility is elaborated on. The development of the simulation and the inputs and outputs of the simulation are discussed before the validation effort. The work conducted on the validation aimed to confirm the accuracy of the simulation unequivocally. Although the production target was not achieved as predicted by the dynamic simulation during the period of validation, there was an indication that the materials handling value chain could perform as predicted as each of the individual sub-systems had achieved the design capacity. Problem areas were identified which could be attributed to the poor performance, and if these areas are addressed, the system could perform as predicted by the simulation. This confirms that dynamic simulation can add value to predictions about mining system performance such that informed decisions can be made.
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    Influence of pit wall stability on underground planning and design when transitioning from open pit to sublevel caving
    (2019) Mapuranga, Amos
    This research sought to address the influence posed by the pit wall stability and instability on underground planning and design when transitioning from open pit to underground. Conventionally, empirical methods are used and they sometimes lack consideration of rock mass behaviour, groundwater effects, structures as well as geological considerations. This can potentially result in massive failures of pit slopes and subsequent loss of infrastructure, excavations, loss of machinery and human lives. It was against this background that this research sought to reduce mining exposure to the above mentioned hazards. In line with the aims and objectives of the study, this research investigated stress changes around the pit slopes with progression of mining and also the influence of geological and geotechnical conditions on mine planning. This was done so as to determine the zone of geotechnical influence from which planning of the underground mine would be done. Elastic 3D numerical modelling approach was used to determine the expected underground back break and its influence on the underground structure, pit slopes as well as the primary access. Different Factor of Safety shells were modelled, so that the corresponding zone of influence for each Factor of Safety could be correlated to the mine design. The results suggested that a Factor of Safety of two was ideal for this research for underground infrastructure to be outside the zone of geotechnical influence from start to finish of mining the first slice until the last fourth slice of the sublevel caving. This approach yield better projections of rock mass and slope behaviour since it considers a broad range of parameters that include rock mass strength properties, geology, geo-mechanical parameters, groundwater and rock behaviour.
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    Application of rock mass classification and blastability index for the improvement of wall control at Phoenix Mine
    (2017) Segaetsho, Gomotsegang Seth Kealeboga
    The study sought to establish the applicability of rock mass classification as a primary input to wall control blasting. Conventional rules of thumb are used to develop blast designs based on parametric ratios with insufficient consideration of the rock mass factors that influence the achievability of final wall designs. Control of the western highwall of the Phoenix pit had proven to be challenging in that the designed catchment berms and wall competence were perpetually unachievable from the pit crest to the current mining levels. This exposed the mining operation to safety hazards such as local wall rock failure from damaged crests, frozen toes and rolling rock falls from higher mining levels. There was also an effect of increased standoff distances from the concerned highwall which reduce the available manoeuvring area on the pit floor and subsequently the factor of extraction that is safely achievable. The study investigated the application of rock mass classification and the Blastability Index (BI) as a means to improve wall control. This was achieved by establishing zones according to rock type forming the western highwall rock mass wherein distinguishing rock mass classification factors were used to establish the suitable wall control designs through a Design Input Tool (DIT). The DIT consolidated rock mass classification methodologies such as the Geological Strength Index (GSI) and the Rock Mass Rating (RMR) and related them to the BI and discontinuities of the rock mass to produce a tool that can be used to develop objective wall control designs. The designs driven by the tool inherently take into account the rock mass characteristic factors at the centre of rock mass classification methods and significantly reduce the dependence on rule of thumb. It was found that this approach yields designs with powder factors that are consistent with the rock breaking effort and the behaviour of discontinuities while remaining biased towards preservation of perimeter wall rock.