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Pillar design and the associated mining engineering constraints in hard rock bord and pillar mines
Dissertation (MSc (Mining Engineering))--University of Pretoria, 2026.
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| Format: | Thesis |
| Language: | English |
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University of Pretoria
2026
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| _version_ | 1869483797519532032 |
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| access_status_str | Open Access |
| author2 | Malan, Francois |
| author_browse | Malan, Francois |
| author_facet | Malan, Francois |
| collection | Thesis |
| dc_rights_str_mv | © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Dissertation (MSc (Mining Engineering))--University of Pretoria, 2026. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/107933 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-07-01T04:04:42.632Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/107933 Pillar design and the associated mining engineering constraints in hard rock bord and pillar mines Malan, Francois wjtheron@icloud.com Theron, Willem Johannes UCTD Sustainable Development Goals (SDGs) Pillar design methodologies Hard rock mining Pillar strength Analytical hierarchy process (AHP) Squat pillar formulae Dissertation (MSc (Mining Engineering))--University of Pretoria, 2026. A limitation of rock engineering designs is that they are often done in isolation, without considering the constraints imposed by practical mining aspects. This study describes some important mining engineering considerations when designing bord and pillar layouts, namely the constraints imposed by the trackless mining equipment used and the requirements for ventilation. The objective of the dissertation was to create awareness of this problem among both mining and rock engineers. This should support the future development of pillar systems that are more productive, effective, and stable. A literature study on pillar design was conducted. A large number of pillar design papers can be found in the academic literature, but almost none of these papers considered any mining engineering or productivity-related topics. Aspects such as productivity, operational and practical mining constraints, ventilation and trackless mobile equipment attributes are noticeably absent from these papers. Furthermore, the large number of different pillar strength equations found in literature should be concerning to any mining engineer as there is no universally accepted design approach for pillars bearing in mind that a wide range of rock mass behaviors will have specific stability considerations that must be addressed. A case study is presented in the dissertation to highlight that the uncertainty in rock engineering, particularly in terms of pillar design, can lead to multiple cycles of design optimisation. Early integration of mining engineering requirements into the design and decision-making processes for pillar layouts would enhance project planning outcomes. Making these considerations during the initial phases of a project enables the development of more effective and robust mine designs. For example, setting up a drill rig is a time-consuming process; it is preferable to minimise repeated setups within a single drilling cycle. In view of these factors, the determination of practical bord widths should not rely solely on rock engineering principles, but the dimensions should also be aligned as closely as possible with the operational capabilities of the available equipment. Furthermore, ventilation becomes onerous for large pillars. Pillar sizes beyond 10 metres will require specialised ventilation controls. This means additional employees per stoping crew with reduced efficiencies. The pillar design methodology currently used requires that progressively larger pillars be used at increasing depths. This will create conflicting requirements once the pillar sizes increases beyond 10 metres as recommended by the rock engineer at a particular depth. An aspect often ignored during the design of pillars is the “squat” effect of pillars for large width-to-height ratios. The "squat" effect of pillars refers to a phenomenon in mining engineering where pillars with a large width-to-height ratio become significantly stronger and behave in a more ductile manner under load than slender pillars (those with a small width-to-height ratio). A squat pillar formula has never been derived for hard rock pillars in the Bushveld Complex. In the absence of any other equation, rock engineers often use the coal squat pillar equation. In this study, a squat pillar formula specifically designed for hard rock was derived, utilising the exponents from the Hedley and Grant equation. This clearly indicates the potential for the significant increase in pillar strength beyond a “critical” width-to-height ratio as it depends on several assumptions. Apart from the pillar strength, there is also uncertainty in the load acting on the pillars. This is an important parameter in the pillar design methodology and is usually approximated using TAT. This is a conservative approach and the modelling conducted for this study illustrated the smaller pillar stress in the presence of nearby abutments and smaller mining areas. This should be considered during pillar design to ensure that an unnecessary additional factor of safety is not included. The study involved two case studies of which the first highlighted two aspects of pillar design in the Bushveld Complex mines that may lead to inefficient layouts and low profitability. The first aspect demonstrated how pillar layout designs are frequently developed without considering other essential and practical mining engineering requirements. Secondly, there are many unknowns in pillar design and the difficulties encountered include the uncertainty in the overburden density, the type of pillar strength formula to use, calibration of the strength formulae and the onset of “squat pillar behaviour” for large width-to-height pillars. To partially address this problem, the study recommends the use of the Analytical Hierarchy Process (AHP) as a decision-making tool for rock engineers to improve pillar layout designs. AHP is especially useful for teams tackling complex, high-stakes design challenges that require consideration of human perceptions. The design of pillar layouts presents a challenge, as rock engineers seek a stable system, which may be overly conservative, while production staff aim for the smallest possible pillars to achieve a high extraction ratio, thereby maximising reserve allocation and mine profitability. The second case study is where the mine must choose between using smaller in-panel pillars with barrier pillars or gradually increasing in-panel pillar sizes without barrier pillars. The differences in extraction ratios for these scenarios are discussed, and the technique favoured the pillar system without any barrier pillars. Future work needs to focus on creating greater awareness among the rock engineers of the conflicting mining engineering requirements, greater use of multi-criterial decision analysis methods such as AHP and verification of the squat pillar behaviour for hard rock. Mining Engineering MSc (Mining Engineering) Unrestricted Faculty of Engineering, Built Environment and Information Technology SDG-09: Industry, innovation and infrastructure SDG-08: Decent work and economic growth 2026-02-06T10:11:18Z 2026-02-06T10:11:18Z 2026-04 2026-01-18 Dissertation * A2026 http://hdl.handle.net/2263/107933 https://doi.org/10.25403/UPresearchdata.31268359 en © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | UCTD Sustainable Development Goals (SDGs) Pillar design methodologies Hard rock mining Pillar strength Analytical hierarchy process (AHP) Squat pillar formulae Pillar design and the associated mining engineering constraints in hard rock bord and pillar mines |
| title | Pillar design and the associated mining engineering constraints in hard rock bord and pillar mines |
| title_full | Pillar design and the associated mining engineering constraints in hard rock bord and pillar mines |
| title_fullStr | Pillar design and the associated mining engineering constraints in hard rock bord and pillar mines |
| title_full_unstemmed | Pillar design and the associated mining engineering constraints in hard rock bord and pillar mines |
| title_short | Pillar design and the associated mining engineering constraints in hard rock bord and pillar mines |
| title_sort | pillar design and the associated mining engineering constraints in hard rock bord and pillar mines |
| topic | UCTD Sustainable Development Goals (SDGs) Pillar design methodologies Hard rock mining Pillar strength Analytical hierarchy process (AHP) Squat pillar formulae |
| url | http://hdl.handle.net/2263/107933 https://doi.org/10.25403/UPresearchdata.31268359 |