Search Documents

By E Matinde, M. Mnisi, I. C. Thobadi, W. Clark, J. D. Steenkamp

Pyrometallurgical smelters utilise tap-holes, through which liquid metal, matte and/or slag are tapped at regular intervals. However, tap-hole failures can have a devastating impact on smelters, which includes loss of equipment, human life and business interruptions. Contributing factors to tap-hole failures include poor and/or incorrect refractory material selection, including tap-hole clays. The functions of tap-hole clays in smelters include their ability to be extruded and drilled with ease at the end and beginning of a tap, and their ability to resist chemical wear due to molten metal and slag during tapping. Mintek is currently developing methods of evaluating properties of tap-hole clays with a specific focus on workability, and wear mechanisms of clays due to ferrochrome alloy and slag. Of particular interest to this study was the characterisation of various tap-hole clays. This paper evaluates the chemical and phase chemical properties of three different tap-hole clays. The bulk chemical composition of the tap-hole clays was determined by inductively coupled plasma optical emission spectroscopy, proximate analyses and combustion methods. The bulk phase compositions and specific phase chemical compositions were studied using quantitative X-ray diffraction, scanning electron microscope and electron probe microanalyses techniques. Keywords: Tap-hole clay, chemical analyses, phase chemical analyses, ferrochrome

Jan 1, 2020

By G. Sahasrabudh, G. DeIulii, K. P. Galvin

A novel agglomeration process has been developed, utilising a concentrated water in oil emulsion as a binder. The binder is typically 95 wt% water, the remainder being an organic phase containing kerosene and the emulsifier— sorbitan mono oleate (SMO) in equal mass portions. The binder can selectively agglomerate hydrophobic particles in less than 7 seconds. The agglomeration has proven to be highly effective in recovering any particle of virtually any size, provided the particle is hydrophobic. The approach has previously been applied to coal, magnetite and silica. In the paper, sodium isobutyl xanthate (SIBX) and its much longer chain version, potassium tetradecyl xanthate (C14X), were used separately as collectors to selectively agglomerate chalcopyrite from the ore. Xanthates attach to metal sulphides, thus hydrophobising sulphide mineral particles. Chalcopyrite is a sulphide mineral; however, it hydrolyses quickly in the presence of water. Ethylenediaminetetraacetic acid (EDTA) was used to remove the oxide layer formed at the surface of the mineral particles after wet grinding, leaving behind a freshly generated metal sulphide surface. After the EDTA treatment, the ore particles were quickly conditioned at an optimised pH as well as collector concentration and agglomerated. The agglomeration achieved a copper recovery of 75% within 7 seconds, consistent with the recovery achieved by flotation over much longer time scales. Keywords: Chalcopyrite, agglomeration, froth flotation, interfacial chemistry, X-ray fluorescence, selective hydrophobisation

Jan 1, 2020

By Z. Luo, W. Chen, Y. Zhao, Y. Fu, L. Dong

The gas-solid dense-phase fluidised bed includes a complex multiphase fluid-particle system; different complex exchanges significantly affect the stability of the fluidised bed. To elucidate the characteristics of fluidisation in a gas-solid dense-phase fluidised bed, this study used experimental performance tests to obtain the static density characteristics, and the attachment and flow characteristic of the dense medium. The results indicate that the bulk density of the dense medium increases first and then decreases with the increase of particle size. The airflow rate difference is used to quantify the wall attachment characteristics of dense medium and the average pressure gradient in the axial direction of the bed is approximately 20 Pa/mm under the fluidisation results. At the same settlement location, with the decrease of fluidisation number, the settlement velocity of large and small particles becomes slower, the boundaries of settlement displacement and location probability are gradually disrupted, and the falling velocity of particles with a radius of 20 mm is faster than that of materials with a radius of 15 mm. This work also established a theoretical basis for regulating the stability and separation characteristics of gas-solid dense-phase fluidised bed. Keywords: Fluidised bed, different size particles, fluidisation characteristics, flotation bubbles, settling motion

Jan 1, 2020

By R. Castro, R. Gómez, F. Betancourt, M. Moncada

In block cave mining, rock fragmentation is a key parameter that influences the production level design and mine planning. Fragmentation occurs mainly by natural breakage during the caving process and in the draw column. The breakage that occurs within the column is known as secondary fragmentation. Secondary fragmentation has been successfully described using the block caving comminution model, which replicates the fragmentation mechanics between particles under drawn and vertical loads in a draw column. This model is based on a kinetic and population balance approach, in which non-normalized and normalized assumptions can be used depending on material and comminution system behaviour. In this paper, the non-normalized and normalized approaches are applied and compared to laboratory data to determine which assumption should be used for secondary breakage in block caving. Approaches are compared graphically, with the mean square error and the Fisher test with a false-rejection probability of 0.05. Based on a statistical analysis, the results show that the normalized model can be applied to all the rock types tested.

Nov 1, 2021

By N. Mangadoddy, M. Padhi

The simulation of multi-component classification with modified viscosity model is the key focus in the current study. The classification of the ores using hydrocyclone is a renowned process and has a convoluted flow separation phenomenon. The highly turbulent flow inside hydrocyclone depends on the operating and design parameters apart from the feed mixture. Slurry viscosity also plays a dominant role in the classification of solid particles under the centrifugal settling action. A heterogeneous mixture with different components would result in different settling and rheological behaviour of particles’ suspension in the water medium. The newly proposed multi-component viscosity model (Mandakini et al. 2020) is implemented as a user-defined function to define the material property during the CFD study of the mixture rheology inside hydrocyclone classifier. The multiphase and turbulence model is solved using the modified Algebraic Slip Model and Large Eddy Simulation model. A comparison of the predicted component performance curves is evaluated with and without the corrected viscosity model. The density and size effect on the particle phase distribution inside the classifier are compared, where the misplacements of the finer particles are carefully assessed. Validation of the component classification in hydrocyclone with the laboratory experiments found a close agreement with the rheology based CFD data. Keywords: Dual-component, multi-component viscosity model, double-gap rheometer, computational fluid dynamics, high solids concentration

Jan 1, 2020

By F. Nakhaei, M. Le Roux, Q. P. Campbell, S. Botlhoko

The results of coal sink and float tests are plotted as washability curves. Analysis of these curves indicates the most effective method by which the coal can be cleaned. Sink and float experiments are samplingdependent, destructive, and use toxic chemicals. The present research introduces an alternative method based on a 3D imaging system called RhoVol, in which the density of individual particles is determined from mass and volume measurements. A quantitative error analysis was conducted on coal sample density measurements obtained by RhoVol, and the main factors influencing the errors identified and investigated. The results show that the drawback of this technique is related to its not being able to detect hidden concavities in the particle, resulting in an overestimation of particle volume. Furthermore, it is difficult to capture the impact of porosity and cracks on the volume of coal particles obtained from 3D silhouette images. This mismatch between the RhoVol data and sink and float test results has led to attempts to apply neural network (NN) and linear regression techniques to produce a fully reliable model for correction and estimation of coal density. The NN approach offers superior predictive capability over linear regression, and the estimated density distribution is in line with the sink and float analysis. The root mean square error in estimation of density using the NN model was less than 0.05 g/cm³.

Aug 2, 2022

By Q. Zhang, X. C. Wang, X. Q. Ao

The flotation separation of apatite and calcium-bearing gangue minerals (dolomite and calcite) has always been a problem in phosphate ore mineral processing research. The crystal structure and surface properties of minerals have an important influence on their floatability. In this paper, the theoretical and comparative analysis of the crystal structure and surface electronic properties of apatite, dolomite and calcite were carried out using the first principle calculation based on density functional theory. As a supplement and validation, the surface wettability of three minerals under different flotation conditions were compared and analysed by contact angle test. The results theoretically revealed that the three calcium-bearing mineral surfaces have similar surface electronic properties and thus exhibit similar floatability. In the flotation process, the anion difference between apatite and carbonate gangue should be fully utilised, and the minerals can be separated only after surface modification by flotation reagent. The contact angle test shows that phosphate and carbonate can be separated by using anion flotation collector after surface modification with acid. It is expected that this research is of interest for understanding the surface structure and electronic properties of apatite and carbonate gangue minerals and providing the theoretical basis for surface interaction. Keywords: Apatite, dolomite, calcite, surface structure, electronic property, density functional theory

Jan 1, 2020

By P. C. Pistorius, D. Kruger, Y. Kacar

Because of its superior properties, stainless steel has been widely used for many applications. Nonmetallic inclusions can influence the quality of stainless steel products. A set of samples was used to track the response of inclusion composition during processing of a heat of titanium-bearing 18% chromium steel, from deoxidation after decarburization, to the solidified slab. The oxide inclusions responded as expected to additions of deoxidizers and calcium treatment, changing from silica to alumina and spinels, and then to calcium aluminates. The samples confirmed that titanium nitride can nucleate on liquid calcium aluminate during steel solidification.

Aug 1, 2021

"SAMPLING: THE IMPACT ON COSTS AND DECISION MAKING1. INTRODUCTIONFor years those in the minerals industry have been taking samples to assist them in making decisions; whether they be about investing billions of rand in a new mining operation, or simply whether a truck load of mineralised material should go to the mill or the waste dump, - we need a sample to help us make our decisions. This paper emphasises the importance and significance of sampling as a process, some of the associated technical problems and some of the advantages, especially in the light of traditional approaches that has usually left mine sampling to the least educated and lowest paid individuals on the mine. Perhaps the most important aspect that requires attention is the variability, usually measured in terms of precision, that tends to infect the sampling procedures. Francis Pitard 12 has stated: ""There is no such thing as reliable feasibility studies, unbiased ore grade control, accurate environmental assessments or effective process control, if you cannot identify and minimize the seven (ten) major sources of sampling variability. "" It is these ten sources of sampling variability and the way they arise that are briefly investigated. Variability is measured in terms of variances and rather than being self-compensating, there is good evidence to indicate that they are in fact additive at every step in the sampling and analytical process."

Jan 1, 2014

By M. Abdellatif

"SynopsisCalcined basic nickel carbonate (BNC) concentrate was smelted in a pilotscale DC arc furnace to produce a nickel metal. The furnace was continuously operated for 12 days (24 hour/day), during which twelve different smelting conditions were investigated, with the major variables being reductant type and feed rate, flux composition and addition, and BNC feed rate.The 200 kW DC arc furnace was operated at power levels between 110 and 165 kW and at a total feed rate of 78 to 96 kg/h, resulting in an average slag and metal tapping temperature of about 1650°C. A total of 7.2 t of BNC were smelted, producing about 5.44 t of nickel metal and 2.94 t of slag. Nickel recoveries of 96.4% and higher were achieved, and the slag nickel content was as low as 0.1%. The major impurities in the metal were iron (mostly from oxygen lancing) and carbon. The calculated feed carry-over was less than 0.85% and the graphite electrode consumption was between 2.8–3.3 kg/MWh.IntroductionOne of the most distinctive advantages of DC open-arc smelting is the ability to process fine raw materials without any major issues with regard to the operability of the furnace, metal recovery, and metal quality. This has been demonstrated in Mintek’s DC arc pilot plant facilities over a period of about three decades (Curr et al., 1983). The materials that have been processed include laterite (Kotze, 2002), chromite fines (Curr et al., 1983), manganese fines (Lagendijk et al., 2010), PGM concentrates (Shaw et al., 2013), electric arc furnace (EAF) dust (Denton et al., 2005; Abdellatif, 2002a) and stainless steel (SS) dust (Denton et al., 2005; Abdellatif, 2002a; Goff and Denton, 2004), and petroleum fly ash (Abdellatif, 2002b). The top particle size of such materials can vary from a few millimetres (e.g. laterite) to micrometres (EAF and SS dust). Dusting, whether due to physical carryover of feed or to the arc side reactions, has been proven to be a non-issue. As such, the applications of DC open-arc furnaces have the potential to be extended to other raw materials such as particulate nickel oxide, which has a particle size much less than 100 µm.Nickel oxide is typically produced from laterite ore by sulphuric acid leaching, purification, and precipitation as basic nickel carbonate (BNC) (Rhamdhani, Jak, and Hayes, 2008) or as mixed hydroxide precipitate (MHP) (Mackenzie, Virnig, and Feather, 2006), and finally calcining at moderate temperatures (800–1200°C). The NiO product is very fine, with an average particle size in the range of 10–20 µm and a NiO content of more than 99%."

Jan 1, 2015

By M. Karsten

Platinum mines in the Bushveld Complex are located in areas with a high geothermal gradient. This means that, compared to, for example, gold mines of the Witwatersrand region, high rock temperatures are encountered at relatively shallower depths. Thus air cooling and refrigeration need to be considered at early stages in mine development. Another factor that influences air cooling and ventilation requirements is the use of trackless diesel equipment for loading and hauling broken rock. At shallower depths it will be more cost-effective to locate the cooling and ventilation equipment on surface, whereas for deeper mines the more cost-effective option is to locate cooling equipment underground. For intermediate depths, trade-off studies need to be undertaken to determine the optimum mix between more cooling and less air or more air and less cooling, as well as the optimum location for this cooling equipment. Factors that are taken into account include power requirements, positional efficiency, and additional infrastructure requirements. Traditionally the approach has been to ventilate ?all of the mine all of the time?. However, with increasing power costs and growing pressure to ensure sustainability, this strategy must be modified to apply ventilation and cooling on demand. In other words, both cooling and ventilation equipment should be operated only when needed and should be adjusted to the demand at the time. Obviously there will be areas that will need to be ventilated (and cooled) continuously (for example, for dilution of flammable gases), but this can be built in to the overall strategy. In addition, in devising ventilation on demand (VoD) strategies, occupational criteria relating to exposure to gases, noise, and heat need to be taken into account. This paper discusses options available for implementing energy-efficient ventilation and cooling systems and suggests ways of changing traditional thinking in the overall ventilation and cooling of mines. Efficient ventilation and cooling designs can play a major role in improving sustainability and reducing energy costs and carbon footprint.

Jan 1, 2012

By C. Zangerl, K. F. Evans, S. Loew

ABSTRACT: Settlements above fractured crystalline rock masses are rarely observed and in the past, geotechnical engineers would not expect substantial subsidence to occur in association with a deep tunnelling project. However, recent high precision levelling measurements along the Gotthard pass road in central Switzerland, have revealed up to 12 cm of subsidence along sections that pass several hundred metres above the Gotthard highway tunnel. Large-scale consolidation resulting from tunnel drainage and pore pressure changes in the rock mass are believed to be the contributing mechanism. This paper presents results from an extensive numerical modelling study focussing on the processes responsible for this subsidence. Results derived from 2-D discontinuum (i.e. distinct-element) and continuum (i.e. finite-element) modelling show that both discrete fracture deformation (i.e. fracture closure and shear) and poro-elastic consolidation of the intact rock matrix equally contribute to the observed magnitudes and shape of the surface subsidence trough. RÉSUMÉ: Des tassements aux dessus de massifs cristallins sont rarement observés et par le passé les géotechniciens ne prévoyait pas de subsidence significative associée avec des projets de tunnel profond. Cependant, de récentes campagnes de nivellement haute précision le long de la route du Col du Gotthard (Suisse centrale), ont mis en évidence des subsidences atteignant 12 cm sur des sections passant plusieurs centaines de mètres au-dessus du tunnel routier du Gotthard. Le mécanisme invoqué pour expliquer ce phénomène est la consolidation à grande échelle due au drainage du tunnel et aux variations de pression de pore dans le massif rocheux. Cet article présente les résultats d’une modélisation numérique intensive mettant l’accent sur les processus responsables pour la subsidence. Ces résultats obtenus grâce à des modèles 2-D discontinus (p. ex. éléments distincts) et continus (p. ex. éléments finis) montrent que la déformation sur des fractures discrètes (fermeture de fractures, cisaillement) ainsi que la consolidation poro-élastique de la roche intacte contribuent également aux magnitudes et aux géométries de subsidence observée en surface. ZUSAMMENFASSUNG: Beachtliche Oberflächensenkungen in einem kristallinen Gebirge, deren Ursache im Vortrieb eines mehrere hundert Meter tiefgelegenen Tunnels liegt, wurden bisher nicht erwartet und beobachtet. Dennoch wurden nach dem Bau des Gotthardstrassentunnels, entlang der Gotthardpassstrasse Oberflächensenkungen mit einem Maximalbetrag von 12 cm bei der Auswertung von Präzisions-Nivellements entdeckt. Dieser Maximalbetrag wurde in einem granitischen Gneis gemessen. Die örtliche Übereinstimmung zwischen dem maximalem Senkungsbetrag und dem maximalem Wasserzufluss zum Tunnel, und die zeitliche Abfolge von Tunnelbau und auftretenden Oberflächensenkungen lassen hydromechanisch gekoppelte Prozesse als Ursache dieser Gebirgsverformungen vermuten. In dieser Arbeit werden die Ergebnisse ausgedehnter prozessorientierter numerischer Simulationen präsentiert. Resultate aus den 2-D Diskontinuum (d.h. distinct-element) und Kontinuum (d.h. finite element) Simulationen zeigen, dass beide Verformungsmechanismen, d.h. an diskreten Brüchen und der intakten Gesteinsmatrix, gleichbedeutend für die beobachteten Senkungsbeträge und der Form des Setzungstroges verantwortlich sind.

Jan 1, 2003

By D. Marcotte, R. V. Dutaut

In most exploration or mining grade data-sets, the presence of outliers or extreme values represents a significant challenge to mineral resource estimators. The most common practice is to cap the extreme values at a predefined level. A new capping approach is presented that uses QA/QC coarse duplicate data correlation to predict the real data coefficient of variation (i.e., error-free CV). The cap grade is determined such that the capped data has a CV equal to the predicted CV. The robustness of the approach with regard to original core assay length decisions, departure from lognormality, and capping before or after compositing is assessed using simulated data-sets. Real case studies of gold and nickel deposits are used to compare the proposed approach to the methods most widely used in industry. The new approach is simple and objective. It provides a cap grade that is determined automatically, based on predicted CV, and takes into account the quality of the assay procedure as determined by coarse duplicates correlation.

May 1, 2021

By S. Durapraj, R. T. Masethe, U. Maqina, A. C. Adoko

This study investigates seismicity and rockburst control within the Merensky Reef and UG2 orebody of an intermediate-depth platinum mine located in South Africa's Bushveld Complex. Utilising a mine-wide seismic monitoring system, over 1,900 seismic events were recorded between April 2023 and May 2024, revealing complex seismic patterns driven by mining-induced stress changes. The largest event, with a magnitude of ML 2.0, underscores the seismic risks associated with mining at increasing depths. Key findings include the spatial and temporal variability of seismic events, with high seismic activity observed near pillars and geological structures. A significant portion of events correlated with pillar and foundation failures. Moment tensor analysis identified dominant failure modes, such as stress-driven fracture closures and dynamic pillar failures. To mitigate risks, the study emphasises advanced support system redesign and rockburst risk assessment using the rockburst damage potential (RDP) method. The research highlights the importance of monitoring, geotechnical compliance, and adaptive designs in enhancing safety and reducing seismic hazards in underground mining operations. The study applied the RDP framework, classifying damage across R1 to R5 scales, where most instances fell into low-risk categories (R1 and R3), indicating minor to moderate damage. However, data limitations and the tabular stoping method's complexity led to inconclusive results, highlighting the need for more robust data and customised risk assessment tools. Despite these challenges, the RDP approach provided valuable insights into rockburst mechanisms and the effectiveness of existing support systems.

Jan 12, 2025

By D. van der Westhuizen, H. Krieg, M. Kruger

In the field of Fischer-Tropsch synthesis catalysts, cobalt, platinum, and aluminium are the primary metal constituents of the conventionally used cobalt catalyst. While platinum recovery remains a focal point in this field, a recent endeavour by a South African company emerged, which aimed to recover cobalt and aluminium from spent Fischer-Tropsch synthesis catalysts for potential use in the agricultural sector. This study aimed to optimally separate cobalt and aluminium from spent Fischer-Tropsch synthesis catalyst for this purpose. It further leverages the OLI database to predict metal speciation during solvent extraction to aid with experimental planning. Shake-out tests were conducted to determine optimal separation. conditions, which were validated using three distinct methods: (i) evaluating the experimental error, (ii) comparing results with similar research, and (iii) validating results against the OLI database. The investigation revealed the pivotal role of the aqueous pH yielding effective separation at pH 3.13 ([H2SO4] = 2.5 × 10−4 M) when using 20 vol.% CYANEX 272 and 50 mol.% pre-neutralisation. Effective cobalt scrubbing was achieved with 50 g/L Al at pH 2.8, while successful stripping required 1 M H2SO4. Competitive interactions between complexing aluminium and cobalt species were observed when contacting with CYANEX 272 at a pH < 4. Equipment design analysis for a targeted separation efficiency of 87% dictated the necessity of two mixer stages and a settler measuring 1.5 m × 1.5 m × 6.0 m (height × width × length). This settler would ensure sufficient residence time for gravity separation at a flow rate of 10 m3/h.

May 27, 2025

By S. Khoshjavan

In this investigation, the effects of different coal chemical properties were studied to estimate the coal Hardgrove Grindability Index (HGI) values index. An artificial neural network (ANN) method for 300 data-sets was used for evaluating the HGI values. Ten input parameters were used, and the outputs of the models were compared in order to select the best model for this study. A threelayer ANN was found to be optimum with architecture of five neurons in each of the first and second hidden layers, and one neuron in the output layer. The correlation coefficients (R2) for the training and test data were 0.962 and 0.82 respectively. Sensitivity analysis showed that volatile material, carbon, hydrogen, Btu, nitrogen, and fixed carbon (all on a dry basis) have the greatest effect on HGI, and moisture, oxygen (dry), ash (dry), and total sulphur (dry) the least effect. Keywords coal chemical properties, Hardgrove Grindability Index, artificial neural network, back-propagation neural network.

Jun 1, 2013

By E. Keskinkilic

In this study, sulfide-type inclusion morphologies of a Ca-treated hot-rolled wheel steel, Grade-X, were investigated. The specimens taken from the hot-rolled products of Grade-X heats were studied. The size and distribution of elongated sulfide inclusions were examined for the heats of different S levels. Elongated sulfide inclusions were either not observed or rarely encountered when ladle analysis S content was below 50 ppm. The size and relative abundance of sulfide inclusions were reported to increase markedly when the S composition was greater than or equal to 70 ppm and the Ca/S ratio was less than 0.50. The effect of Ti addition (0.010?0.020% Ti) on sulfide-type inclusion morphologies was then investigated for heats having a sulfur content higher than 50 ppm. Addition of Ti was found to have a partial effect on decreasing the size of sulfide-type inclusions under real steelmaking conditions. Keywords Sulfide inclusions, Ca-treatment, titanium.

Jan 1, 2011

By E. Bakhtavar

There are many near-surface deposits with considerable vertical extent that have the potential to be mined by a combined method of open-pit and underground methods. In this regard, there is often a point called ?transition depth? where a decision has to be made whether to continue deepening the pit or change to underground methods. Recently, optimization of the transition from open-pit to underground operation has become an important challenge in mining engineering. Optimally, to model the transition problem on the basis of maximization of the profit from open-pit and underground mining, (0-1) integer programming has been used. In this method, block economic values of open-pit and underground methods should be imported to the transition model. A hypothetical example is presented in order to assess the model in detail.

Jan 1, 2012

By A. Golder, S. P. Dandapat, I. Roy

One of the consequences of large-scale opencast mining for coal is the disposal of an enormous volume of overburden material that needs to be removed. With the enlargement of opencast mines and associated high stripping ratios, the volume of overburden extraction is rising. Overburden from the initial mine cut has to be necessarily dumped outside the mining area until enough void is created inside the mine for back-filling operations. The quantity of overburden placed outside the mining area normally varies from 10% to 30% of the total overburden removal. The stability of these dumps placed outside the mining area is of prime importance from the point of view of smooth operations of the mines and safety of persons in and around the dumping area. Owing to increasing pressure on land use, mine operators do not have any other option other than to place the waste dumps very near to the surface edge of the pit, which may lead to failure of the topsoil benches of the working pit. This study identified major controlling parameters that influence a stable but economic combination of height and slope angle of external dumps located close to the edge of an open coal pit.

Nov 27, 2024

By J. A. Maritz, D. F. Malan

Pillar strength is affected by pillar shape, but this has largely been ignored in past research studies. Bord-and-pillar layouts are typically designed using empirical strength equations developed for square pillars. Owing to the poor quality of pillar cutting, many hard-rock pillars have an irregular shape and it is not clear how this affects pillar strength. Furthermore, the strength of rectangular pillars in comparison with square pillars is also difficult to quantify. The ‘perimeter rule’ is widely adopted for rectangular pillars, but its applicability for pillars with irregular shapes has never been tested. We used numerical modelling in this study to investigate the effect of pillar shape on strength. An analytical limit equilibrium model of a square and a strip pillar also provided useful insights. For slender pillars, the strength of a long rib pillar is essentially similar to that of a square pillar. In contrast, for rib pillars with a large width to height ratio, there is a substantial increase in strength. The study found that the perimeter rule should not be used for irregularly shaped pillars. Displacement discontinuity modelling, using a limit equilibrium approach, is proposed as an alternative to determine the strength of these pillars.

May 3, 2023