3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Pillar stability analysis from secondary extraction at Goedehoop Colliery’s No.2 Seam(2018) Banda, ChikondiThe 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.Item Review of techniques for identification of underground bord and pillar workings(2018) Govender, Ganasen LoganathanThe 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.Item Investigations into the effect of size and width to height ratio on the strength of the laboratory sized coal specimens(1996) Canbulat, IsmetThe design of bord and pillar working in South African collieries is based on the pillar strength formula developed by Salamon and Munro1967 and which has been used widely since then for designing pillars. This formula is based on the statistical analysis of 27 collapsed and 98 intact coal pillar cases from collieries located in the Transvaal and the Free state. The main objective of this study is to establish the difference in the strength of the coal material in ditferent seams by means of laboratory testing. In this manner, some 753 coal samples from 10 collieries from 4 seams were tested. The size and width to height ratio effects on strength were analysed. The size effect showed that the difference between the seams was obvious, with a difference of 59,4 per cent between the strongest and weakest coal. The statistical re-analysis showed that the strength of the six blocks from the No 2 seam, Witbank Coalfield occurred in a fairly tight strength range; and that laboratory coal strengths from individual seams or mines could deviate to a significant although relatively small extent from the overall average.Item Design guidelines for pillar and rib pillar extraction in South African collieries(2016-07-20) Beukes, Johannes StephanusPillar 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.