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By L Dyer, G. J. Wilkie, P. Walters, B Tadesse, L. Keeney

Grade Engineering® is a term trademarked by the Cooperative Research Centre for Optimising Resource Extraction (CRC ORE) and includes five key levers for upgrading ores and rejecting waste prior to expensive downstream comminution and mineral processing. These five levers include natural deportment, induced deportment, bulk sorting, particle sorting and gravity separation. Over the past ten years, CRC ORE has progressed a range of technologies that exploit these levers from laboratory proof of concept through to large scale demonstration and validation. This paper details the work carried out by CRC ORE and Curtin University for assessing the amenability of an ore for its natural deportment and particle sorting attributes in an Integrated Screening and Particle Sorting (ISPS) Grade Engineering® process. ISPS is seen as a preferred method for Grade Engineering® as compared to individually operated unit operations as the benefits of each can be complementary. Furthermore, it is suggested that integrating the two levers has two important impacts: 1. Firstly, there is a risk that isolated particle sorting test results will be misinterpreted as being representative of the full sample without considering the mass balance impact of high-grade material that might have been lost in the fines fraction. This fine fraction will not be detected through the particle sorter. 2. Secondly, and potentially of more valuable impact, is that the opportunity may exist to upgrade the feed first through determining if there is a concentration of high grade to the fine (or coarse) fraction which can be separated through screening. Undertaking screening in the preparation stage of the particle sorting process will enable analysis and separation of the fine or coarse fractions of a rock mass. The result of this study provides the mining industry with an independent framework for undertaking an Order of Magnitude (ISPS) Grade Engineering® assessment on a range of constituent ore types. Keywords: Grade engineering, particle sorting, grade by size fractionation

Jan 1, 2020

By S. Sekhar, S. Bhargava, A. K. Godugu, J. L. Porathur

Cemented backfilling has enabled underground hard rock mines to extract orebodies more safely with improved ore recovery. It is important to estimate the minimum required strength parameters for a backfill mix by optimizing the binder percentage to enable cost-effective and safe stoping operations. We conducted three-dimensional numerical modelling to study the effect of various stoping parameters on the stability of a free-standing backfill wall. A Mohr-Coulomb material model was used for the backfill material and the rock-fill interface. A strength reduction technique, excluding friction angle, was employed to arrive at a minimum stable strength value for the backfill. For a given combination of strength values, the stability state of the backfill wall could be demarcated using a displacement and yield zone tracking method. The numerical modelling results are compared to some earlier theoretical models. From the simulations, a predictive equation is developed to predict the required strength parameters for a backfill mix to ensure a stable free-standing wall. Examples are given of the successful use of the predictive equation at some underground hard rock mine sites in India.

May 2, 2022

By S. Schutte, J. Pelders

Worker participation in equipment development can result in improved user acceptance and product quality. This paper focuses on worker engagement in equipment development processes in the South African minerals sector. Qualitative data was gathered during interviews with original equipment manufacturers (OEMs) and industry experts. A lack of inclusion in equipment design from workers from all organizational levels in mines was reported. Meanwhile, the historical context and workplace culture of the mining industry (including leadership, trust, training, performance, and remuneration factors) were evident barriers to the implementation of new technology. Worker engagement processes should include securing management commitment, creating multidisciplinary teams, effective facilitation, shared understanding of needs, training and development, and iterative design. Human-centred design approaches and independent platforms for engagement on equipment design requirements are recommended.

Feb 2, 2021

By G. Coetzer

"Prior to operating a non-recovery coke pilot plant oven, it was essential to ascertain coal cake stability during the loading of a 1 m3 (1 m × 1 m × 1 m) coal cake into the cold pilot-plant oven by a pusher mechanism. Previously established laboratory-scale compaction parameters, to obtain coal cakes with sufficient stability, were employed during the loading tests of the coal cakes. Two different coals were evaluated, namely Waterberg semi-soft coking coal (sscc) and Oaky North hard coking coal.It was demonstrated that lower applied compaction forces (14%) can be utilized during 1 m3 compaction, in comparison to laboratory-scale tests, to obtain similar wet cake densities, owing to differences in the effect of frictional forces. Wet cake densities for Waterberg sscc improved slightly (3%) to 1.13 t/m3 when utilizing 79 t/m2 applied force for a 1 m3 coal cake, in comparison to laboratory-scale tests. Similar results were obtained for Oaky North hard coking coal, with a 6% density increase to 1.27 t/m3 at a similar applied force. Porosities decreased by 13% and 32% for Waterberg sscc and Oaky North coal, respectively, when 1 m3 compaction was compared to laboratory-scale tests. An opportunity exists to further decrease the porosities of Waterberg sscc during compaction, whereas acceptable compaction parameters were achieved for Oaky North hard coking coal. Most major vertical cracks and the partial collapse of coal cakes were mitigated, and high-stability coal cakes were obtained that could be successfully loaded into the pilot-plant coke oven by a pusher mechanism.Factors contributing to the instability of the coal cake during loading into the oven, such as vertical cracks, are (i) the cubic geometry (1 m3) of the coal cake, (ii) friction exerted by the oven floor, and (iii) mechanical problems, such as a misalignment between the pusher machine feeder plate and the oven floor. IntroductionOperation of the stamp-charging horizontal 1 t electrically heated coke pilot-plant oven at Exxaro Resources requires coal cake stability during the loading of a 1 m3 compacted coal cake into the oven. In this case, a pusher plate is utilized to push the coal cake into the oven over the oven floor. This is in contrast to a ‘spoon’ or bottom plate feeding mechanism as found in industrial horizontal coke ovens. The pusher plate loading mechanism dictates that the coal cake should possess high stability and inherent strength owing to frictional forces exerted by the oven floor. In order to obtain a coal cake of acceptable stability for the 1 t coke oven, various compaction parameters need to be verified and established."

Apr 1, 2019

Notices STRASZACKERREPORT The Institute has received, for its information, a copy of the following letter, which was addressed to The Federation of Societies of Professional Engineers: REPORT: COMMISSION OF ENQUIRY INTO THE METHODS OF TRAINING FOR UNIVERSITY DEGREES IN ENGINEERING (STRASZACKER REPORT) Geagte Heer, VERSLAG: KOMMISSIE VAN ONDERSOEK NA DIE METODE VAN OPLEIDING VIR UNIVERSITEITSGRADE IN INGENIEURSWESE (STRASZACKERVERSLAG) Second International Symposium on Jet Cutting Technology This symposium, sponsored and organised by BHRA Fluid Engineering, of Cranfield, England, is to be held at St John's College, Cambridge, from 2nd to 4th April, 1974. Competition for student members of the South African Institute of Mining and Metallurgy Each year the Institute offers a prize (or prizes should the entries warrant it) of up to R100 for the best paper or dissertation on a topic appropriate to the interests of the Institute. Techomin 74 - World Mining Fair The above World Mining Fair, under the sponsorship of the International Committee for the Organization of World Mining Congresses and the Peruvian Government, is to be held in Lima, Peru, from 3rd to 12th November, 1974, to coincide with the 1974 World Mining Congress, which is to be held in Lima. NIM Reports Report No. 1435 The determination of chromium, manganese, iron, cobalt, and nickel by atomicabsorption spectrophotometry using the nitrous oxide-acetylene flame. Report No. 1463 Liq'uidus temperatures and activities of manganese (11) oxide in slags associated with the production of high-carbon ferromanganese alloys. Report No. 1467 The spectral analysis of solutions. 1. The analysis of rare-earth minerals. Report No. 1479 Infrared studies of the adsorption of oleate species on mineral surfaces,with special reference to fluorite. Report No. 1483 The South African manpower requirements in extractive metallurgy. Report No. 1484 Cost estimates for the production of copper wirebars from sulphidic ores. Report No. 1486 Review of the jluoro-chemical industry of the World. Report No. 1490 The adsorption of krypton, nitrogen, and water vapour on sodium oleate. Report No. 1491 Technology and economics of the Olaus kiln under South African conditions. De Beers Report The dry grinding of tungsten carbide/ steel combinations with diamond wheels. Metallurgical Directory The Israel Export Institute has just published the first edition of the Israel Metal Industry Directory, which gives pertinent information relating to the 750 Israeli manufacturers of metal products-addresses, annual turnover, and products- and to consulting engineers and export companies specializing in metal products. Visiting Nuclear Scientist The National Institute for Metallurgy has announced that Professor Vincent P. Guinn, of the University of California, is to spend his sabbatical leave (April to June) working with the Activation Analysis Research Group of the National Institute for Metallurgy.

By D. J. Briggs

The use of backfill for regional and local support is receiving increasing attention in the South African mining industry. To ensure that fill materials meet the purposes for which they are intended, a test procedure to characterize the load-deformation characteristics for a particular fill was developed. The major variables identified as influencing the load-bearing proper- ties of backfill include particle size distribution, porosity, width-to-height ratio, strain rate, confinement, water content, and additives. The influence of these variables on the performance of backfill is described in relation to crushed waste, dewatered tailings and deslimed tailings. These investigations confirmed that no single test could be used to define the overall stress-strain behaviour of a selected fill. Nevertheless, resulting from this work, a preliminary standard test procedure for uncemented backfill materials, com- prising a suite of tests in unconfined and confined compression, has been formulated. This test procedure is a significant advance towards a more meaningful evaluation of fill materials. Test results will also provide numerical information for input use in computer programs for the design of mine layouts incorporating backfill.

Jan 1, 1988

By C. J. Liebenberg

This paper focuses on the application of ion exchange technology for the recovery of copper from a leach solution originating from a heap bioleach in which base metals are leached from a low-grade ore that bears platinum group metals. Screening tests indicated that Dow XUS43605 has high selectivity for copper over the other metals in the solution, namely nickel, iron, cobalt, zinc, manganese, and aluminium. Batch adsorption kinetic experiments showed that copper adsorption equilibrium is attained at a fast rate. The kinetics of adsorption increased as the temperature was increased from 25°C to 60°C due to the decrease in solution viscosity and the subsequent improved intra-particle mass diffusion. Single-component Langmuir and Freundlich isotherm models were fitted to the batch copper adsorption equilibrium data, and a maximum copper capacity of 26 g/l was observed for Dow XUS43605. The effects of flow rate, temperature, pH, and initial metal concentration on the dynamic recovery of copper were investigated in fixed-bed columns, and it was determined that temperature and flow rate had the most significant impacts on the loading of copper on the resin at copper breakthrough. A 36% increase in copper loading at breakthrough was observed when the temperature was increased from 25°C to 60°C. Finally, it was determined that a split elution is possible by using different concentrations of H2S04 to first elute co-loaded nickel from the resin, followed by the elution of copper.

Jan 1, 2013

By C. J. Lenz

The results of prospecting operations involving geological data and a large number of geochemical determinations of the metal content of soil samples are plotted and evaluated by computer. Anomalous areas are identified in each type of environment by selecting probability or population boundary values from frequency distributions. The anomalies are plotted to permit correlation with geographical or geological features. Ranking of prospecting targets is made using geographic pattern, geology, absolute value and metal ratios. Three short case histories are presented.

Jan 1, 2014

By T. M. Louw, L. Auret, S. M. Bradshaw, F. F. Noelle

Modern industrial processes undergo frequent process state shifts due to changes in demand, feedstock or maintenance operations. Multimodal continuous process monitoring is therefore required for effective plant operation. Steady state analysis is a key component in effective multimodal monitoring. Various issues still remain in determining the starting and ending times of transition states. High dimensionality of process data is a characteristic that makes it difficult to select variables to consider when conducting steady state analysis. In order to address these problems, steady state detection on the principal component space is proposed. First, data undergoes principle component analysis to reduce dimensionality, then existing multivariate steady state detection algorithms are applied on the principle component scores. A novel algorithm, threshold PCA-SSD, is proposed and compared to an existing technique for steady state detection. The algorithms are investigated on high dimensional synthetic data Keywords: Multimode process, steady state detection, principle component analysis

Jan 1, 2020

By T. B. Beeton

In view of the limited reserves of good-quality coking coals in South Africa, Iscor has been involved in direct reduction since the middle sixties. Since the early seventies, its interest in direct reduction was stimulated further by a swing towards' continuous casting, which, in turn, contributed to a shortage of the scrap supply for electric-arc-furnace (EAP) steelmaking. Rock engineering The First International Conference-Rock Enginet:ring and Excavation in an Urban Environmentorganized by The Institution of Mining and Metallurgy and the Hong Kong Section of the Institution, in association with the Hong Kong Institution of Engineers, will be held in Hong Kong from 23rd to 28th February, 1986. SPOTLIGHT on Gold Fields National Engineering Awards For the Gold Fields Foundation National Engineering Awards, each university affiliated to the South African Federation of University Engineering Students (S.A.F.U.E.S.) selected a candidate who, in their opinion, presented the most outstanding design project in their final year during 1984.

Jan 1, 1985

Visit to the Datsun Nissan Company's body pressing and assembly plant at Rosslyn, Pretoria, and the Claremont-Danville Tunnel on 27th February, 1970. The excursion arranged for the 27th February to the Datsun Nissan motor car assembly plant at Rosslyn, near Pretoria, in the morning and the Claremont-Danville tunnel in the afternoon was well supported by some 43 members. The visitors were met at the factory by Mr Rademeyer, the Industrial Relations Manager, and members of his staff and were taken to the artisan training centre for light refreshments. There is a well-equipped training section with an air-conditioned lecture hall; we were told that such training facilities were important because of the cosmopolitan nature of the artisan staff. The visitors were divided into small parties and taken to the tool die and jig-making section, which is perhaps the key department for a factory of this nature. There the many dies for the presses in the body pressing section, as well as the complicated jigs for body welding are made. The technique for making the castings for the dies is interesting. A polystyrene model of the casting is embedded in moulding sand. In a neighbouring foundry molten metal is pressed into the headers and burns away the polystyrene, which leaves no residue, and this exactly fills the space occupied by the model. This rough casting is then machined in large copying machines (costing as much as Rl80 000). An exact plastic model of the surface of the pressing required, set up in juxtaposition to this casting is traversed by a master stylus which operates the slave milling cutter, thereby machining the surface to close tolerances. The machined casting is cleaned up by hand and finally finished in large spotting machines, using a blue dye to show up high spots, to the fine degree of accuracy required. The body pressing section was next visited. There the large number of pressed parts which make up a vehicle body are pressed out of special deep drawing steel plate. Some of the largest presses were capable of applying a pressure of 1 200 tons and cost as much as Rl85 000 each. The visitors then followed through to the assembly section where jigs are used to hold together the many pressings, which are then spot welded into body frames. The frames go to an assembly line where they are finished to the stage for painting. The continuous crawl painting assembly line carries the frames through all the stages of prime coating with zinc phosphate sprayed on in a tunnel, followed by immersion of the lower parts in a priming bath, then drying and spray painting and baking in tunnels. The body frames, after painting, join another assembly line, where the doors, upholstery and many fittings are attached. After this stage the completed bodies are lowered onto and attached to the chassis units which are largely assembled from imported parts (engines, transmission units, etc.). From the end of the line the completed cars are driven off to the trial track and then pass through a tunnel with powerful water sprays to detect leaks in the body work. The proportion of locally made parts is just on 45 per cent. An interesting aspect of the assembly organization is that, of the 140 or 160 cars completed each day there may be included some of each of the Datsun model as well as some Renault and Alfa Romeo models models which are assembled by this company. The change from one model to another several times a day does not present any difficulty to the organization. Each section of the assembly plant 'buys' the units from the preceeding section and 'sells' to the succeeding section. This means that the responsibility of each section ends when the unit is sold to the next section. The cost of repairing any faults found subsequently is charged to the section where it is found, which puts a powerful emphasis on meticulous inspections between sections to safeguard their costs. After the tour the parties assembled at the lecture hall where a lavish cold buffet luncheon was provided by the company. After luncheon Mr A. R. C. Fowler, on behalf of the Institute, thanked the Managing Director, Mr W. J. Wilson and his staff for this most interesting and well organized visit. The party then left for the Claremont-Danville tunnel. The tunnel is being driven by General Mining Federale Kontrakteurs through the Daspoort Range, Pretoria, to link the suburbs of Danville, near Iscor, and Claremont, which at present can only be reached by a nine mile detour. It is estimated that some 6000 vehicles per day will use the tunnel. Before entering the tunnel a short talk was given by Mr Ross who is in charge of operations. He called on various officials and staff of the Consulting Engineering firm, Basil Read (Pty.) Ltd., to describe the tunnel and

COUNCIL AND STANDING COMMITTEES, 1974-1975 Office Bearers : Prof. R. P. Plewman (President), Dr R. E. Robinson and Dr M. D. G. Salamon (Vice Presidents), J. K. E. Douglas (Honorary Treasurer), and P. W. J. van Rensburg (Immediate Past President). Elected Members of Council: Dr M. G. Atmore, E. Collier, G. H. Grange, Dr P. R. Jochens, Dr D. I. Legge, D. G. Malan, C. T. Shaw, L. W. P. van den Bosch, D. A. Viljoen, H. M. Wells, P. A. von Wielligh. Branch Chairmen: B. T. Hosking (Witbank-Middelburg Branch), D. A. Smith (Orange Free State Branch). Past Presidents Serving on Council: R. J. Adamson, M. Barcza (until May 1975), H. Britten, H. E. Cross, Prof. J. de V. Lambrechts (until December 1974), R. C. J. Goode, Prof. D. D. Howat, Dr J. P. Hugo, D. M. Jamieson, D. G. Maxwell, Dr J. T. McIntyre, V. C. Robinson. Ten Council meetings were held during the year, with an average attendance of 19, and the standing and sub-committees held 74 meetings. COMMITTEE CHAIRMEN Membership, Dr M. D. G. Salamon; Technical Programme-Metallurgy, D. A. Viljoen; Technical Programme-Mining, G. H. Grange ; Vacation School-Metallurgy, Dr P. R. Jochens; Vacation School-Mining, Dr M. D. G. Salamon; Awards, Prof. R. P. Plewman; Excursions, Dr D. I. Legge; Constitution, Rules and Policy, P. W. J. van Rensburg and Prof. R. P. Plewman; Mines and Works, P. A. von Wielligh; Education, P. W. J. van Rensburg. REPRESENTATIVES ON OTHER BODIES Associated Scientific and Technical Societies Members: V. C. Robinson and Prof. R. P. Plewman. Alternates : Dr R. E. Robinson and Dr M. D. G. Salamon. Federation of Societies of Professional Engineers Members : J. K. E. Douglas and P. W. J. van Rensburg. Alternates : Prof. R. P. Plewman and G. H. Grange. South African Council for Professional Engineers Member : R. C. J. Goode. Alternate : G. H. Grange. Engineers' Liaison Committee (Pretoria) Member: Dr J. P. Hugo. Alternate: P. W. J. van Rensburg. MEMBERSHIP Thirteen Fellows, seventeen Members, eleven Graduates, three Associate Members, eighteen Associ¬ates, twenty-six Students, and one Company Affiliate were elected during the year. Nine Fellows, four Members, and three Associates were admitted to retired membership. Eight Fellows were elected to Honorary Life Membership. Three Members and one Graduate were transferred to Fellows, nine Graduates and two Students to Members, six Students to Graduates, one Student to Associate, and one Associate to Associate Member. Six Fellows, ten Members, three Associates, and one Student resigned. A statement of membership as at June 30th 1975 and the end of the previous year is shown in the following tabulation: 30th - 30th June, - June, 1974 - 1975 Honorary Life Fellows - 9 - 15 Honorary Fellows 8 - 8 Life Fellows 170 - 170 Fellows 544 - 536 Members 512 - 523 Associate Members 10 -15 Graduates 130 - 133 Associates 194 - 210 Students 173 -175 Company Affiliates 70 - 71 1 820 - 1 851 [ ] OBITUARIES Your Council records with deep regret the death during the year of the following members: M. Barcza, Honorary Life Fellow and Past President of the Institute; J. A. Boyd, F. E. Keep and J. H. Taylor, Life Fellows; I. D. B. Corner, C. O'G. Deane, R. E. Gilmour, A. C. Hofmeyr, M. W. Howell, T. J. Robin and F. C. Steinhobel, Fellows; J. J. Frankel, Member; T. J. Higgs, Associate. FINANCE The annual accounts, which follow this report, indicate that income again exceeded expenditure by a margin of R21 410 (last year R28 524). This year's income of R71 184 showed a further increase compared with last year's figure of R55 025. Costs, however, also in¬creased, and it is calculated that, excluding non-recurrent costs, the cost of running the Institute in¬creased by R6 654 from R25 501 to R33 155 for the current year. The main increases were involved in secretarial fees, stationery and print¬ing, and in publication of the Journal. All indications are that costs will continue to rise, and we have been advised that the A.S. & T.S. will be increasing their secretarial fees by 25 per cent in the year ahead to meet their rising costs. This year's surplus was derived entirely from the revenue from sales of publications (R13 644) and a surplus from the 1974 Winter School (RIO 654). There can be no certainty that revenue from these sources can be repeated each year. Our funds are in a satisfactory position because of these worth¬while activities, but the administrat¬ion of the Institute should not de¬pend on them. Council will accord¬ingly have to give consideration in the year ahead to an upward adjust¬ment of subscriptions to meet rising costs.

Jan 10, 1975

The AMIRA Code of Practice and Guidelines for Metal Accounting was developed in response to demand from a number of sponsor companies, including one major platinum producer. Since its publication in 2007, the Code has become widely accepted in the mining industry world-wide as a guide for best practice in metal accounting. With the changes in the structure of the platinum mining industry in South Africa over the last 10 ? 15 years, in particular, the starting up of a number of small platinum producers who must have their concentrate smelted and the contained valuable metals refined by third parties, the need for metal accounting systems that are accurate and have an acceptable level of precision has become even more critical to the success of a platinum-producing operation. The current state of metal accounting in the industry is discussed and possible areas for improved accounting and associated metallurgical efficiencies are identified.

Jan 1, 2012

By T. Vincent, J. Steele, C. Debrunner, M. Whitehorn

This paper presents current work on the development and use of stereovision for underground mining. Information on the calibration of the cameras and the feature-matching algorithm are presented. This system uses an intensity-based approach that evaluated correspondences along the epipolar line. Once features have been identified and their distance from the cameras computed, a three-dimensional map of the muck pile is developed. The approach used here uses a ray-tracing algorithm. This approach provides an uncertainty measure along with the elevation. A discussion of the use of this modelling information in the control of the LHD is included. Keywords: Robotics, automation, LHD, underground mining, vision sensing, task automation, tele-operation

Sep 1, 2001

By Allan Jansen, Robin Bissett

[Power-Point Presentation]

Jan 1, 2005

By Gordon Chunnett, Ron Sheets, David Grant

[Power-Point Presentation]

Jan 1, 2005

By D White, L. Lorenzen

Sampling and metallurgical testwork during various phases of engineering studies is of paramount importance for a robust processing plant design. When developing a process flowsheet, risks in achieving desirable financial outcomes are minimised by ensuring that appropriate sampling and adequate metallurgical testwork support the engineering and cost estimation at each phase of project development. The quality and type of samples used for metallurgical testwork are just as important as the metallurgical testwork itself. The key characteristic required of any sample is that it represents some defined portion of a mineral deposit. Representivity should consider the spatial orientation, lithology, alteration, degree of oxidation, mineralogy, and competency of the ore such as hardness and abrasiveness. Statistically representative sampling procedures and an appropriate metallurgical testwork program should be designed to bring metallurgical understanding up to feasibility study standard and to give a basis for process plant design. The authors have observed that the quality of sampling and quantity of metallurgical testwork carried out during the various phases of engineering studies are often insufficient to truly support a robust plant design. Some designs are based on benchmarks of apparently similar ore bodies or rely on buoyant metal prices supporting cash flows until rectifications can be implemented. The paper will discuss important aspects of sampling and testwork required for engineering studies in designing process plants. Keywords: Sampling, metallurgical testwork, studies, design

Jan 1, 2020

By G. Howell, J. Wates, A. Coetzee, C. J. MacRobert

The Global Industry Standard on Tailings Management (GISTM) requires mining companies to make four key appointments as part of their tailings management structure. These four positions are an Accountable Executive with policymaking responsibilities, a Responsible Tailings Facility Engineer with operational responsibility, an Engineer of Record to ensure facilities are designed, operated, and closed safely, and an Independent Tailings Review Board to assess safety drivers regularly. Little guidance on the traits of these individuals is available in a South African context. Consequently, the tailings community of practice was surveyed to develop a table of ideal competencies and establish the flexibility in meeting these traits.

Jun 2, 2022

By G. van Aswegen

The geometry and morphology of a set of low-angle fractures around a stope in a deep Witwatersrand gold mine are explained in terms of extension fractures forming under variable conditions of stress. Primary extension fractures (E1) form some distance ahead of an advancing stope along the s1, s2 plane. With stope advance, a couple of these fractures end up in a stress regime conducive to transpressional shear and a secondary set of extension fractures(E2) is formed at a high angle to the primary fractures. i.e. at a low angle to the stope. As the E2 fractures are undermined, they migrate into a stress regime of transtensional shear and a third set of extension fractures (E3) may develop between E2 fractures. These have sigmoidal shapes, being parallel to the E2 fractures at the E2 discontinuity where s3 is negative, and curved through the unfractured rock between E2 fractures where s3 is positive at the instant of fracturing. The fractures all display fractographic features characteristic of dynamic extension failure with striae indicative of the direction of rupture propagation and the local, instantaneous orientation of s1.

Jan 1, 2012

By G. M. Evans, S. Mitra, G. J. Jameson, M. M. Hoque, E. Doroodchi, R. Moreno-Atanasio

In this study, the detachment behaviour of 314 μm diameter silica particles from a single 3 mm diameter bubble rotating in a confined cavity connected to a cross-flowing water channel was investigated. The liquid cross-flow generated a rotating flow inside the confined cavity, which was quantified using 2D particle image velocimetry (PIV) measurements. The fluctuating (x-y) velocity components inside the cavity for each cross-flow velocity, U, were then used to estimate the corresponding time/volume average turbulence intensity values, Ti. Turbulence intensity ranged from 9.3-16.2%. In the absence of a bubble, the rotating vortex within the cavity created a pressure field which decreased towards the centre of the vortex; wherein the lowest pressure zone was located at the centre of the cavity. The vorticity into the cavity was found to increase with increasing the turbulence intensity. A bubble, both without and with particles attached, was introduced into the cavity under different flow conditions and its motion was tracked using the shadowgraphy technique. Experimentally, it was found that the bubble-particle aggregate was trapped at the centre of the cavity (low-pressure region) following a spiral trajectory. An interface resolved 3D computational fluid dynamics (CFD) model was developed to predict the particle detachment conditions within the confined cavity. CFDpredicted vorticity in the absence of a bubble agreed well with experimental observation. The CFD analysis indicated that the vorticity inside the cavity was not significantly changed when a single bubble was introduced. On this basis, the computed vorticity was utilised in describing the force balance applied to the attached particle. Computationally, it was found that the critical turbulence intensity, beyond which the particle was detached from the bubble, was 14%. This value was consistent with the experimental observation of detachment at Ti at 15.7%, and above, but not at lower values. Keywords: Bubble, particle, turbulence intensity, vorticity, particle detachment, CFD, PIV

Jan 1, 2020