Search Documents

By Z-P. Song, Z-B. Jiang, A-N. Jiang

"In deep excavations under conditions of high ground stress, even hard rock undergoes creep and other time-dependent effects that may result in instability. This study involves an analysis of the typical damage to the surrounding rock in the deep tunnels of the Jinchuan nickel mine in China. In order to understand the creep mechanism, triaxial creep laboratory tests were conducted under high stress. The creep characteristic curves and the Nishihara model parameters of typical rock were obtained from these tests. The numerical simulations, with which the creep model is developed, were performed using Flac3D. The creep model parameters were back-analysed on the basis of field monitoring data. Finally, appropriate support schemes for deep tunnels are suggested. The creep deformation of rock increases with time and axial load. At the same load level, the creep deformation of unloading is greater than that of loading. The simulated deformations of the surrounding rock are coincident with those from in situ monitoring, indicating the applicability of the presented rock creep model in situations of high ground stress. The results constitute a reference for support design in deep mining tunnels.IntroductionThe excavation of underground caverns can alter the natural stress field of the surrounding rock. In deep engineering projects under conditions of high ground stress, even hard rock shows obvious creep properties and time effects (Yao, 2005; Liu, 1994). The time effect of excavation not only causes decompression of the floor and increases sidewall stress, but also leads to stress concentration at the corners of the excavation, which influences the stability of the surrounding rock in a very complex manner.Many researchers have studied the creep properties of rock. ‘Griggs (1939) showed that creep occurs in sandstone, shale, and silty sandstone rock under the load of 12.5%–80% of the failure load.’ Subsequently, much research has been published on rock creep tests, including the uniaxial compressive creep test, the triaxial compressive creep test, the discontinuity rock shearing test, and field tests (Wawersik, 1974; Amadei et al., 1980; Okubo et al., 1991; Jin et al.,1995). A rheological model is used to describe the complex rheological deformation of material. This model is based on various fundamental parameters including rock elasticity, plasticity, and viscous properties, which can be combined into a constitutive model to reflect the rheological properties of various types of rocks. Wang et al. (2014) studied the creep– damage–rupture characteristics of rock salt by applying a creep-damage model. Munson (1997) developed a multi-mechanism constitutive model of creep of polycrystalline rock salt based on steady-state creep and modified it to incorporate transient creep through work hardening and recovery. An elasto-viscoplastic approach was developed to simulate the timedependent nature of the fracture zone (Malan, 1999). Rheological models were proposed to understand the collapse of iron ore mines in Lorraine by Dragan et al. (2003)."

Jan 1, 2016

By J. W. Klokow, S. L. Mulder

Early removal of the shaft reef is usually considered necessary on deep level South African gold mines to avoid damaging stress build-up associated with traditional shaft-protection pillars. In the case of the relatively shallow Beatrix Gold Mine it was largely motivated by early access to ore and the consequent earlier return on invested capital. A number of options were considered to protect the shaft from possible damaging stress changes and to minimise deformations in the shaft-reef area. Numerical modelling was used to evaluate the options and to quantify as accurately as possible the likely deformations to be accommodated by the shaft steelwork designs. The option chosen was a combination of strategically placed satellite pillars and yield pillars, and backfill. Following the mining of a small inner cut during the shaft sinking process, full-scale mining is progressing away from the shaft. Suitable instrumentation has been installed to monitor deformations associated with the shaft reef removal. Enlever rapidement le filon du puits est en général considéré nécessaire dans les galeries de fond des mines d’or sud-africaines pour éviter l’accumulation nuisible de contraintes associée aux piliers de protection de puits traditionnels. Dans le cas de la mine d’or Beatrix, relativement peu profonde, l’enlèvement était motivé en grande partie par l’accès rapide au minerai et par conséquent un profit plus rapide sur l’investissement. Un certain nombre d’options furent considérées pour protéger le puits contre les changements de contraintes potentiellement nuisibles, et pour minimiser la déformation dans l’aire puits/filon. La modélisation numérique fut utilisée pour évaluer les options et pour quantifier aussi précisément que possible les déformations probables que la conceptualisation du puits devrait prendre en compte. L’option choisie fut une combinaison de piliers satellites placés à des points stratégiques avec des piliers de protection, et terre de remblayage. Pendant le fonçage de puits une petite coupure intérieure fut exploitée, et maintenant l’exploitation à grande échelle, au-delà du puits, est en cours. Les instruments nécessaires ont été installés pour surveiller les déformations associées à l’enlèvement du filon du puits. Die frühe Entfernung des Riffschachtes wird normalerweise bei südafrikanischen Tiefbaugoldmienen als notwendig erachtet um den zerstörende Druckaufbau zu vermeiden, welcher mit traditionellen Schachtschutzpfeilern verbunden ist. Im Fall der verhältnismäßig flachen Beatrix Goldmine war es hauptsächlich vom frühen Zugang zum Erz und dem konsequenten frühen Rückfluß des investierten Kapitals motiviert. Eine Anzahl an Optionen wurde erachtet um den Schacht vor möglichen zerstörenden Druckänderungen zu schützen und Deformationen im Riffschachtbereich zu minimieren. Um die Optionen zu bewerten und mögliche Deformationen so genau wie nur möglich quantitativ darzustellen die von den Schachtstahlkonstruktionen aufgenommen werden müssen, wurden numerische Modelle verwendet. Die gewählte Option war eine Kombination aus strategisch plazierten exzentrischen Pfeilern und Schutzpfeilern sowie Hinterfüllungen. Nach dem Vortrieb eines kleinen inneren Einbruches während des Abteufens wird der Vollvortrieb vom Schacht weg vorgenommen. Um die Deformationen, die mit der Riffschachtentfernung verbunden sind zu überwachen, müssen geeignete Instrumentenausrüstungen installiert werden.

Jan 1, 2003

By S. Budavari, F. M. C. C. Vieira

For several decades, the deep, gold-bearing reefs of the Witwatersrand basin have been mined predominantly according to layouts characterised by longwalls with strike pillars to provide regional support. During the past few years, a new generation of mining layouts has been introduced. These layouts are based on the concept of grid-type, scattered mining with dip pillars for regional support. As the extraction of the gold reefs extends to depths below 3500 m, the hazards associated with mining at these ultra-depths are expected to increase to unacceptable levels. Therefore, the question arises as to, which of the currently applied mining layouts is most acceptable for the economic and safe extraction of an ultra-deep orebody. The purpose of this paper is to describe a research investigation carried out to evaluate the degree of acceptability, from the rock engineering view point, of four currently used mining layouts for application at a depth-range of between 3500 and 5000 m. Pendant plusieurs décades, les filons d’or profonds du bassin du Witwatersrand ont été exploités d’une manière prédominante selon des dispositions caractérisées par des longues tailles avec des piliers directionnels pour donner un support local. Les dernières années ont vu la naissance d’une nouvelle génération de dispositions de mine. Ces dispositions sont basées sur le concept d’extraction type grille, éparpillée, avec des piliers au pendage pour le support local. Comme l’extraction des filons d’or va à des profondeurs en dessous de 3500m, il faut s’attendre à ce que les risques associés à l’exploitation à ces profondeurs extrêmes atteignent des niveaux inacceptables. Par conséquent, la question se pose de savoir laquelle des dispositions de mine couramment utilisées est la plus acceptable pour l’extraction rentable et sans danger d’un gisement ultra profond. Le but de l’étude présente est de décrire les recherches exécutées pour évaluer le degré d’acceptabilité, du point de vue d’ingénierie de roche, de quatre dispositions de mine couramment utilisées pour application à un rayon de profondeur entre 3500 et 5000m. Die tiefen, goldträchtigen Riffs des Witwatersrandbeckens wurden über einige Jahrzehnte hindurch vorwiegend nach jenen Layouts abgebaut, die von Langfrontstreben mit Schlagpfeilern charakterisiert waren, um regionale Unterstützung zu gewährleisten. Während der letzten Jahre wurde eine neue Generation von Grubenlayouts eingeführt. Diese Layouts basieren auf dem Konzept der Rasterfeld-Art, gestreuter Bergbau mit Neigungspfeilern für regionale Unterstützung. Es kann erwartet werden, daß auf Grund der Tatsache, daß sich die Extraktion der Goldriffs auf Tiefen unterhalb 3500 m verlagert, die Gefahren, die mit dem Bergbau an diesen Ultratiefen verbunden sind, sich auf ein nicht annehmbares Niveau erhöhen. Folglich erhebt sich die Frage, welche der gegenwärtig angewendete Abbaulayouts für die ökonomische und sichere Extraktion eines ultra-tiefen Erzkörpers am annehmbarsten ist. Zweck dieser Arbeit ist es, eine durchgeführte Untersuchung zu beschreiben, die vom Gesichtspunkt der Gesteinstechnik gesehen, vier gegenwärtig angewandte Abbaulayouts für den Einsatz in einem Tiefenbereich zwischen 3.500 und 5.000 m evaluiert.

Jan 1, 2003

The Third International Conference on Coal Research was held in Sydney, Australia, in October 1976. The papers and proceedings of the Conference will be published in Australia on behalf of the International Committee for Coal Research in April 1977. The papers deal with the economics and practicability of coal conversion, coal winning, resources assessment, safety and dust, and coal and power generation, together with an appreciation of coal potential by the deputy chairman of the U.K. National Coal Board. Copies of the report are available to organizations within member countries of ICCR at a cost of 35 dollars (Australian), including postage, by application to the Executive Officer, Third ICCR, Box 3842 GPO Sydney, Australia 2001. Drafts should be in Australian currency payable to Third International Conference on Coal Research.

Jan 6, 1977

By P. C. van Aswegen

The Schools A school on 'Measurement, Process Control and Optimization in the Minerals Industry', organized by The South African Institute of Mining and Metallurgy, was presented twice by course leader Dr Ken Garner, ably assisted by the staff of the Measurement and Control Division of Mintek. The first school was held from 16th to 20th July, 1984, at the University of the Witwatersrand, and the second from 11th to 15th February, 1985, at Mintek. Project development The Sydney Branch of the Australasian Institute of Mining and Metallurgy will hold a second Project Development Symposium in Sydney between 7th and 10th October, 1986. This second symposium will extend the range of topics covered by its predecessor in 1983 to emphasize planning (including strategic planning), construction, and project commissioning.

Jan 1, 1985

By T. C. Marshall

A comparison between hydraulic and pneumatic rockdrills by T. C. Marshall, Pr.Eng. (Member) The greatly increased output of rockdrills has placed new demands on booms, carriers, and drill steels and bits. Limited scope for further improvement in pneumatic rockdrills has led to the development of hydraulic rockdrills, which compare favourably with their pneumatic counterparts: they are more efficient, more flexible in coping with variations in the working conditions, more economical in the consumption of drill steel, and less productive of noise and mist. Their disadvantages include a greater need for a reliable power supply, a greater vulnerability to dirt, greater complexity (requiring more skilful maintenance), and the liberation of heat into the working environment. They should be regarded as a complement to, and not as a substitute for, pneumatic rockdrills.

Jan 2, 1974

By J. de V. Lambrechts

A critical comparison of specific cooling power and the wet kata thermometer in hot mining environments By J. de V. Lambreehts. D.Sc. (Eng.) (Rand) A new formula for the wet kata thermometer has been established in place of the currently used one which is believed to be fundamentally wrong and the new formula is compared with the recently proposed specific cooling power concept. Apart from a constant multiplier, it is concluded that the difference between. the two concepts lies solely in the value of 'n' in the function vn and that this value for the cooling power of air on the sweating human body remains to be established reliably. The kata thermometer might yet be found to be a reliable predictor of heat stress in hot environments.

By J. J. Van Rensburg

The commissioning of a test facility for the calibration of anemometers by J. J. VAN RENSBURG (Student Member). After the erection of a commercially produced open-jet wind tunnel for the calibration of the anemometers used in mine ventilation, the wind tunnel was calibrated for routine use. There is a choice of five orifice plates. which, together with a variable-speed fan, can give a measurable range of air velocities in the test section from about 0,05 to 35 m/so The orifice plates were calibrated against a standard pitot tube, and it is now necessary only to measure the pressure drop across an orifice plate and to read off, from a set of graphs, the true outlet velocity in the test section. The paper describes the underlying theory and the test results.

Jan 4, 1975

By D. A. Viljoen

The ore mined at Black Mountain is of a complex nature, being composed of both magnetic and massive sulphides, which have greatly varying metal values. Because of this, there is need for a rapid method of assaying for the continuous monitoring and control of the process streams, and the Outokompu Courier onstream analysis system and the Proscon process-control computer systems have therefore been installed. Geostatistics In view of the continuing demand, the Department of Mining and Mineral Sciences in association with Special Courses Division, Department of Adult Education and Extramural Studies, both of the University of Leeds, will offer two further courses on A Practical Introduction to Geostatistics in 1981, each covering ten working days. The courses will run from 30th March to 10th April and 14th to 25th September.

Jan 1, 1980

By P. R. Janisch

This paper reviews the sources, production, and technology of gold in South Africa. First of al it details the geographical distribution of gold-bearing materials, together with the mineralogy and distribution of gold within those materials. It goes on to the geological origins, and to the discovery and early exploitation, of the gold deposits. The laws relating to the mining and disposal of the metal are explained, after which an outline is given of gold exploration, processing, and refining. The economics of gold production are discussed briefly, and it is concluded that, although present expertise in the financial and technological aspects of a gold-mining venture have largely reduced the risks involved, one severe risk remains: that the rate of cost inflation will not be matched by the rate of escalation in the gold price.

Jan 1, 1986

By C. Rodrigues

This investigation compares the gas adsorption behaviour and capacity of three bituminous coals from South Africa, of similar rank, by assessing the characteristics of the raw coal, as well as the resulting float and sink fractions (at 1.80 cm3/g) obtained by density separation of crushed coal samples. Calculations were also made to obtain the raw coal gas storage capacity from the weighted contribution of both float and sink fractions results, thereby permitting comparison with the analysed results of the raw coal. The study demonstrated that the clean fraction of a coal has the highest capacity to retain gas in the sorbed state, followed by raw coal, and lastly the sink fraction, and re?confirmed previous investigations that showed minerals to be inhibitors of gas adsorption and retention.

Jan 1, 2008

1. Book reviews Mining and metallurgical practices in Australasia. Melbourne, Australian Institute of Mining and Metallurgy, 1981. $40 (incl. surface postage). Reviewer: M. G. Atmore Coal mine ground control, by Syd. S. Peng. 1978. Reviewer: C. F. Engelbrecht Sixth Annual International Conference on Coal Gasification, Liquefaction and Conversion to Electricity, July 31 -August 2, 1979. Pittsburgh, School of Engineering of the University of Pittsburgh, 1980. Reviewer: S. T. J. van Rensburg This book is a useful general reference volume on the topics covered provided a great deal of technical detail is not required from it. It consists of 29 papers, which are arranged under 6 headings. Flotation agents and processes. Technology and applications, edited by M. W. Ranney. Park Ridge, D.S.A., 1980. $48. Reviewer: R. P. King 2. New books Project control manual, by Sven R. Red. 250 pp. in loose-leaf binder. U.S. Al47. (Obtainable from the author at Bray Studios, Windsor Road, Windsor SL45 UG, England.) Manganese deposits, by Supriya Roy. London, Academic Press, 1981. 400 pp. Joint preparation for welding (set of overhead-projector transparencies). Abington (England), The Welding Institute, 1980. £34 per set. Electron micrographs of clay minerals, by T. Sudo,S. Shimoda, R. Yotsumoto, and S. Aita. Amsterdam, Elsevier, 1980. 228 pp. Dfl.150. Weld pool chemistry and metallurgy. Abington (England), The Welding Institute, 1980. 357 pp. $27. 3. New journal ...being known as Gliickauf + Translation, at an annual subscription of 396 DM for 24 issues per year. It is available from Verlag Gliickauf GmbR, D-4300 Essen I, P.O. Box 103945, Federal Republic of Germany. 4. Canadian MRI publications During 1980 the Mineral Policy Sector introduced a new series of reports identified by the prefix MRI. These cover internal studies and analytical works on a wide variety of subjects, that for one reason or another, do not reach the publication stream of the regular series yet may be of interest to readers in this 'unpublished form'. Twenty-four such titles are listed below. Exploration planning A series of professional advancement seminars for the mineral industry is to be held at Rhodes University from 12th to 20th August, 1981. The series, entitled 'Economic Guidelines for Exploration Planning', will be conducted by Professor B. W. Mackenzie, and the attendance will be limited to 30 participants. The seminars are intended Seminar on Geostatistics A seminar for mining executives on Geostatistics and Decision Making in the Mining Industry is to be held in Toronto from 23rd to 25th September, 1981. v

Jan 1, 1981

By P. J. D. Lloyd

This fascinating paper deserves study by all who are interested in the economics of gold production. The argument in the paper that price is determined by the balance between supply and demand may be thought to be obvious. However, correlation analysis presumes causality, and there is some evidence in the paper to suggest that causality is absent in this market.

Jan 1, 1984

By P. R. Jochens

It is interesting to note that, when the Technical Programme Committee-Mining first decided on this particular topic for a colloquium, the proposed title was different in that it used the words 'rising price of gold'. The very fact that the title was reworded to use the words 'fluctuating gold price' highlights the problem that faces the South African gold-mining industry.

Jan 1, 1981

By A. N. Brown

Underground rock boring was the topic of the mining vacation school held at the University of the Witwatersrand in the week 4th to 8th February, 1980. The School, which dealt with the management and economics of the subject, attracted 75 delegates from all sectors of the South African mining industry, in addition to two delegates from Germany and one from Zambia.

Jan 1, 1980

By R. F. Botha

I want to thank you for inviting me to deliver this, the closing address at the final plenary session of the 15th Congress of the Council of Mining and Metalurgical Institutions. Your Council has an impressive title, and justly so. Consider the expertise, the skill, the capacity, the achievement, that is gathered together here in this room this afternoon.

Jan 1, 1994

By J. Meintjes

by I. J. BARKER and A. B. STEWART J. MEINTJES I read the above paper with considerable interest. I would like to point out, however, that it is fallacious to conclude that the adverse effects of a high inductive reactance on furnace operation can be cancelled by connecting capacitors in series - or for that matter, in shunt - with the power supply.

Jan 1, 1980

By By the staff of Gold Fields of South Africa

A diamond-drilling programme conducted from 1971 to 1973 by the Phelps Dodge Corporation revealed three complex sulphide ore-bodies in the highly folded Namaqualand mobile belt on the farm Aggeneys, some 65 km west of the small town of Pofadder on the road to Springbok in the northwestern Cape. Of these, the Broken Hill occurrence is the most promising.

Jan 1, 1980

The authors and Iscor's management are to be congratulated on an interesting and detailed paper that discloses Iscor's philosophy, strategy, and action concerning what can also be termed productivity improvement. Aside from the pioneering work of Beeforth and Dicks regarding Dynamic Profitability Analysis at Vaal Reefs, there appears to be a shortage of papers on this topic from the mining groups.

Jan 1, 1990

By T. V. Owen

This paper describes the flotation of cassiterite from fine slimes at Rooiberg Tin Limited, and gives an of the Amdel on-line analysis system that was instaled in 1984 to aid in the control of the concentrate The system, which is easy to install and maintain, and which uses X-ray-fluorescence analysis, has improved control, and therefore a better recovery of tin.

Jan 1, 1988