Mabuza, Rekson Steven2023-04-112023-04-112022https://hdl.handle.net/10539/34962A research report submitted in partial fulfilment of the requirements for the degree of Master of Science in Engineering to the Faculty of Engineering and the Built Environment, School of Mining Engineering, University of the Witwatersrand, Johannesburg, 2022The main objective of this research study is to identify factors that cause coal losses and dilution when underground coal pillars are exposed through opencast mining methods, and to find ways to reduce the negative impacts of these factors. The opencast mining methods used in the exploitation of underground coal pillars involve the blasting of pillars with overburden and collapse the bords before exposure by draglines, trucks, and shovel fleets. This research study also aims to answer the main research question relating to the current causes of both dilution and coal losses, and interrogate if the existing bonus incentive scheme promotes the motivation for employees to send more waste material with the run of mine coal into the crushing plant. To achieve the main purpose and answer the research questions, research methods such as the application of multi-criteria decision methods, simulations using software such Science RS2 and 3DDig, and application of empirical formulae to calculate pillar scaling were extensively used in this study. By using these methods, it was found that coal losses were mainly caused by the following factors: • Roof coal losses take place due to blast shear and exposure equipment such as draglines and shovels scalp coal during exposure. The scalping happens because of inaccurate coal pillar profile sent to the monitoring system designed to assist operators with visibility of the plan to be followed; • The other coal loss happens on the floor due to accumulation of water which the mine struggles to control in the coaling face and hard coal left on the floor because of exposure equipment cycling the pit at a faster rate and catching up with the coal extraction process before all the coal can be extracted, and • Geological and geotechnical factors were also found to contribute immensely towards coal losses in the mine. In terms of dilution causes, strip orientation and the current incentive scheme were found not to cause dilution in the mine. The main causes of dilution were found to be a combination of pillar scaling and current blasting practice, mode of failure when bords are collapsed and methods used to blast pillars before exposure. These causes are not currently considered because the mine assumes that the pillar shape and size have not changed since the creation of pillars some years ago. When the coal pillar methods were reviewed with multi-criteria decision methods, it was found that bord collapse with the cleaning of waste between pillars was found to be the suitable method. However, if pillar implosion is to be used, the review found that pillar implosion with coal pillar loss of 26.5% was found to be an appropriate method. The main recommendation for this research study is to adopt the bord collapse method with cleaning between pillars across all the pits. This method can only be successful if a detailed sequence is developed with the operators and introduce a monitoring system where a coal pillar plan can be loaded into the coal loading equipment. However, if the mine wants to continue to use pillar implosion in some of the pits, the current bench setup and method should be changed to allow coal blending from the pit. The required blending ratio to reach plant yields of above 60% is two blocks of high quality upper seam coal which are not been mined previously and one block of imploded coal pillar. The imploded coal pillar must be cleaned up to the top of the predicted profile leaving waste on the lowest points in the profile.enDissertation