ETD Collection

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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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    Analysis of pillar/rockmass failure and propagation dynamics due to mining in hard rock Platinum Mines
    (2018) Mushangwe, Patrick Chenjerai
    The propagation of failure of a pillar system has often resulted in catastrophic consequences, this research establishes key variables that govern failure propagation in hard rock platinum mines. In order to critically analyse failure propagation, the available literature was reviewed to guide the research on key focus areas that may govern propagation. A review of the global and local geotechnical environment was done leading into detailed analysis of the data and rock mass behaviour from a case study mine to establish key variables and behaviour correlations. Available literature point towards failure largely due to mining practice issues and to some extent ground conditions. Joint orientation has been proven, in literature, to have an influence on the strength of pillar systems in particular when the joints dip adversely at 45° to the pillar / loading axis. This research also establishes that ground conditions, as described by rock mass quality and the effect of major sub-horizontal shear structures on pillar systems, have significant influence on the direction of failure propagation. This research further establishes that the failure prefers a direction 45° to the major vertical to subvertical joint set. The angle between the direction of migration and major subvertical joint is a phenomenon that had not been largely explored in terms of influence on failure propagation. The influence of mining practice issues, like pillar position and factor of safety, on failure direction is comparatively lower. This research also shows that barrier pillars should be designed taking into account the strike of major subvertical joint sets/structures in order to improve the ability to stop the propagation of failure. The analysis of the ground monitoring parameters, closure rates in particular, can be used to inform evacuation plans and reduce the impact of failure propagation on safety and production.
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    Pillar stability analysis from secondary extraction at Goedehoop Colliery’s No.2 Seam
    (2018) Banda, Chikondi
    The current outlook for coal within the global energy market compels South African based collieries to re-strategize their current methods of extraction, with the decline of coal reserves within the Witbank coalfield. An economically feasible alternative would be secondary extraction methods that are relatively low in financial and safety risk. However, efficient mining can only occur where optimal rock engineering practices are used. The No. 2 Seam (thickness of about 6m) has always been a favoured deposit for extraction within Goedehoop colliery, consisting of ‘good quality’ economical coal. Where previously mined at about 4.5m, a possible 1.5m remains either in the roof or floor for extraction (when mined in conjunction with the No.1 seam in areas of thin seam parting). Despite the remaining coal having the potential to be included in future plans, the current concern is the stability of pillars within panels associated with the progressive failure due to minimal roof support and poor rock engineering design, without accounting for the risk of failure. If the failure of the pillars were to occur, it will cause the sterilization of the No.4 seam that is currently being mined above the No. 2 Seam. A bottom/top coaling case study was looked at Goedehoop colliery with the aim to evaluate the stability of pillars within the panel/s using stability criterions (Factor of Safety, Probability of Failure and Probability of Survival). Using the pressure arch theory and applicable strength equations to the No.2 seam, the stability of individual pillars was evaluated, where previously coaling had taken place. The results estimated the likelihood of failure of the pillars within the selected panel. The results from the study showed that if and where coaling has taken place it is likely that the pillars would remain stable well above the FOS value limit of 1.6 and resides within the 99% POS limit of production panels.
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    Subsidence caused by high extraction coal mining in the Sasolburg and Secunda areas : prediction thereof and the mitigation of its effects
    (1991) Van der Merwe, Jacob Nielen
    The thesis describes the results of research which was done over the period 1985 to 1990 in the Sasolburg and Secunda areas into the effects of underground high extraction coal mining on the surface, surface structures and agriculture. Legal restrictions on the undermining of structures potentially sterilize more than 30% of the coal reserves in the study area. The basic motivation for doing the research was that most of the restrictions could be overcome if methods could be developed to undermine structures safely and economically. For subsidence data analysis, a computerised three dimensional method of analysis, the Surface Element Analysis (SEA) approach, was developed and implemented. Using the results of the analyses and analytical considerations, a subsidence profile prediction method was developed. The prediction method incorporates a new approach to the prediction of strain, based on the shape of the subsidence profile and the thickness of deformable layers on surface. The reactions of various commonly occurring structures in the study area, namely bituminised roads, gravel roads, pipe lines and conveyor belts, to subsidence were analysed. It was found that although no consideration to subsidence was given in the design of the structures, most could withstand the effects thereof safely with only minor and relatively inexpensive precautionary and repair measures. With regard to agriculture, it is shown that while there are mining induced effects, they are in general not severe. There is, however, reason for concern regarding the long term and not immediately apparent effects. Further work is thus very necessary. Overall, it was found that while a very cautious approach to high extraction undermining had merits in the past, most of the restrictions can be relaxed in the light of the knowledge which is now available. The important provision is that careful and detailed prior investigations are necessary for each individual case, and that a sound and responsible engineering approach must be followed. Mines can derive substantial economical benefit from the mitigation methods which are described. A very important aspect is the administrative handling of the undermining of structures. A coordinated multi disciplinary approach, catering for communication and joint planning of mining and infrastructure, is proposed. It contains the essential elements of the Australian approach with modifications for local South African conditions.
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    Review of techniques for identification of underground bord and pillar workings
    (2018) Govender, Ganasen Loganathan
    The higher quality virgin coal resources in the Witbank Coalfield are near completion, hence new methods of mining the underground coal pillars that have been left insitu as primary support becomes attractive to mine using opencast methods. Up until 2006 more than three million pillars have been created (van der Merwe, 2006) and have been growing since. There are various challenges associated with pillar extraction via opencast mining method. These challenges relate to spontaneous combustion, underground water and the exact spatial location of underground pillars that have been mined in the early to mid-1900. The reliability of old underground mine plans pre-1960, before the Coalbrook disaster, saw underground pillars not being offset which resulted in unreliable survey plans (van der Merwe, 2006). This report focuses on possible techniques that can be used to identify underground pillars where no water and no spontaneous combustion are evident. The following two methods have been tested: Ground Penetrating Radar (GPR) technique which is based on geophysics and a down the hole 3D laser method using the Cavity, Auto-scanning, Laser System (CALS Tool) which uses reflectorless principles to measure the geometries of the underground pillars. The GPR did not provide any conclusive data, whilst the CALS Tool provides detailed information of the workings. The CALS Tool is not practical to identify every single pillar in a reserve but can be used on a larger extent as a short term mine planning mechanism. The CALS Tool proved to have the ability to identify the spatial location of the underground workings as confirmed by the test done at TOC.
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    Reflections on support design in geotechnically challenging group conditions: a case of Zimbabwean great Dyk platinum mining
    (2018) Chikande, Tonderai
    Falls of ground pose costly hazards to personnel and equipment and thus measures should be taken to prevent them. The stability of excavations is ensured by good support design and sound mining practices. This research endeavours to analyse and improve the support systems used in geotechnically challenging ground conditions for Great Dyke platinum mines by analysing the current support systems and recommending effective support system thereof. Various techniques were used to determine the quality of ground conditions, predict the rock mass behaviour and to identify the appropriate support system. An analysis of the current ground control methods and their limitations was also undertaken. The reflections showed that the current support system and mining practices in geotechnically poor grounds need to be modified to improve safety and productivity. Stoping overbreak is influenced by poor ground conditions and the explosives currently used. The use of emulsion is recommended to replace ANFO. Redesigning of pillars through a reviewed design rock mass strength is also recommended taking into cognisance the current rock mass data. Pillar staggering was also seen as the best practice in geotechnically poor ground conditions in a bid to limit exposure. An evaluation of the current tendon system indicated an opportunity for improvement following comprehensive empirical and analytical design techniques. A new support system was recommended, taking into consideration cost-benefit analysis to clamp overlying layers as well as the catastrophic wedges. Barring down using pinch bars in poor ground was seen as a risky and time-consuming exercise, hence the use of mechanical scalers is recommended to achieve zero harm and to meet production targets. Smoothwall blasting is recommended in poor ground to minimize hangingwall damage. The results gathered and analysed showed that, technically, emulsion explosives are beneficial but the increase of operational cost down-weighs them. However, in solution to the problem which prompted this research, the author suggests the mines to take up emulsion as it promotes safety at higher productivity in terms of tonnage output. Other recommendations include the use of hydrological surveys to determine groundwater levels and implement corrective measures. Both empirical and numerical modelling approaches need to be utilized in determining the optimum support. Additional support is also recommended where there is pillar robbing and pillar scaling to increase the pillar strength. Poor support design and poor mining practices pose danger to employees, resulting in loss of profitable reserves and entrapment of expensive mining machinery thereby culminating in additional capital costs and reduced life of mine.
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    Design guidelines for pillar and rib pillar extraction in South African collieries
    (2016-07-20) Beukes, Johannes Stephanus
    Pillar extraction using 'handgot' methods has been practised in South African collieries fOJ' many years. During the late Sixties pillar extraction with mechanized conventional equipment commenced, and approximately a decade later, continuous miners were introduced into pillar and rib pillar extraction panels. During the years that these mining methods were practised, a vast amount of experience was gained on the various collieries. Problems were experienced by various mines and the management of these mines made numerous alterations to the mining methods with varied degrees of success, Research was 0.150 conducted by COMRO and by V,\ri01l5 mines and mining house". Apart from the recommendations of Salamon and Oravecz (1976) on pillar design in stooping sections, little information has been published and, thus, little is generally available to mine managers, planners and operators to assist them in the layout and design for plllar and rib pillar extraction. A survey of all the pillar and rib pillar practises, past and present, has been conducted for collieries in South Africa and abroad and the successes, failures, problems experienced, changes made to the mining methods and the results of these changes have been documented. The problems and successes experienced, t~ similarities and difference between mines and mining methods, and the research flndlngs have been assessed and evaluated. Design guidelines relevant to the various methods of pillar and rib pillar extraction have been established to improve the safety and performance of pillar extraction operations. These guldellnea ate not intended to be prescriptive but are designed more to bring to the attention of the mine manager, planner and operator those fllctors which should be taken into consideration during the planning and operation \)f a pillar Ot rib pillar extraction panel. In addition to the strata related factors, the economics of the mining method is important to determine if it is beneficial to do secondary ext-action, and also to assist in optimlsing the secondary extraction. The design prlnclplns were therefore appUed to diffcrtmt panel layouts, pillar sizes and extraction sequences to determine the effect on the production costs.