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By R. A. Puchner

The location of a decline shaft portal can have far reaching implications if the geotechnical conditions are not suited for safe and cost effective excavation. Ideally the portal should be positioned in an area where the excavation requires minimal support and the portal can be formed in reasonably competent rock. In many cases, however, the shaft is linked to an underground mining plan and the shaft may have to pass through poor ground conditions. Determining the optimal position at which tunnelling can commence i.e. the portal, is critical and requires a thorough geotechnical investigation. Methods used to acquire information for the assessment of the ground conditions are discussed in this paper. Selection of the appropriate methods is dependent on the anticipated ground conditions, the phase of investigation and restrictions due to site access and budget. Non-invasive techniques are often used during preliminary phases and invasive techniques for the detailed investigation. The methods used during each phase of investigation are discussed. Two case studies are then presented to provide examples of the investigative methods used in two different environments. The first being a flat featureless site with thick soils and deeply weathered bedrock, while the second is a mountainous site with differentially weathered rocky outcrops. Based on these cases, it is clear that an understanding of the geology and geomorphology of the site is vital to the final geotechnical assessment. Key words: Decline shaft, boxcut, geology, geomorphology, geotechnical, portal.

Jan 1, 2009

By R. A. Puchner

The location of a decline shaft portal can have far reaching implications if the geotechnical conditions are not suited for safe and cost effective excavation. Ideally the portal should be positioned in an area where the excavation requires minimal support and the portal can be formed in reasonably competent rock. In many cases, however, the shaft is linked to an underground mining plan and the shaft may have to pass through poor ground conditions. Determining the optimal position at which tunnelling can commence i.e. the portal, is critical and requires a thorough geotechnical investigation. Methods used to acquire information for the assessment of the ground conditions are discussed in this paper. Selection of the appropriate methods is dependent on the anticipated ground conditions, the phase of investigation and restrictions due to site access and budget. Non-invasive techniques are often used during preliminary phases and invasive techniques for the detailed investigation. The methods used during each phase of investigation are discussed. Two case studies are then presented to provide examples of the investigative methods used in two different environments. The first being a flat featureless site with thick soils and deeply weathered bedrock, while the second is a mountainous site with differentially weathered rocky outcrops. Based on these cases, it is clear that an understanding of the geology and geomorphology of the site is vital to the final geotechnical assessment. Key words: Decline shaft, boxcut, geology, geomorphology, geotechnical, portal.

Jan 1, 2009

By Y. Mitani, M. Xie, G. Zhou, T. Esaki

The assessment of landslide instability and risk has become a topic of major interest for both geoscientists and engineering professionals as well as for local communities and administrations in many parts of the world. In this paper, based on a new developed Geographic Information Systems (GIS) grid-based 3D deterministic model and taken the slope unit as the study object, the landslide hazard is mapped by the index of the 3D safety factor. Assuming the initial slip as the lower part of an ellipsoid, the 3D critical slip surface in the 3D slope stability analysis is obtained by means of a minimization of the 3D safety factor using the Monte Carlo random simulation. The failure probability of the landslide is calculated by an approximate method in which the distributions of f,c and the 3D safety factor are assumed to be in normal distributions. The assessment of the earthquake triggered landslide hazard is done by the dynamic displacement analysis using the index of the Newmark displacement. All the calculations are implemented by a computational system call 3DSLOPEGIS in that a GIS component is used for fulfilling the GIS spatial analysis function. Besides the results of 3D safety factor and probability, the possible landslide body and boundary can be three-dimensionally quantitatively identified. L’ estimation des glissement de terrain et des risques impliqués est devenu un des principal sujet de préoccupation pour les géotechniciens, mais aussi pour les ingénieurs specialisés ainsi que pour les communautés et administrations locales dans de nombreuses région du monde. Dans cette étude, basé sur un modèle de maillage 3D et une approche déterniniste couplée au Système d'Information Géographique (SIG), étudiant la stabilité des versants , le lieu d'étude à risque est maillé suivant le facteur de sécurité calculé en 3D. En supposant que le glissement initial soit la partie inférieure d'un élipsoïde, l'analyse de stabilité pour le glissement critique 3D d'un versant 3D est obtenu grace à une minimisation du facteur de sécurité en 3D utilisant la méthode de simulation aléatoire de Monte Carlo. La probabilité d'un glissement de terrain est calculée par une méthode approximative, supposant la distribution de c, f et du facteur de sécurité 3D normale. L'estimation d'un risque de glissement de terrain causé par un tremblement de terre est faite grace à une analyse du déplacement dynamique suivant l'index de Newmark. Tous les calculs sont effectués par le biais d'un système de calcul appellé 3DSLOPEGIS dans lequel te GIS est utilisé pour gérer l'analyse spatiale. En plus de cela, les résultats du coefficient de sécurité en 3D, des probabilités, le terrain susceptible de glisser, et ses limites, peuvent être quantitativement évalués en trois dimensions. Die Bewertung von Erdrutsch-Instabilität und risiko sind zu einem Thema von großen Interesse für sowohl Geowissenschaftlern und Ingenieuren als auch von Gemeinden und Verwaltungen in vielen Teilen der Welt geworden. In dieser Arbeit, basierend auf einem neu entwickelten Geografische Informationssysteme (GIS) gitterbasierten 3D deterministischen Modell und mit der Böschung als Untersuchungsobjekt wird die Erdrutschgefahr durch den Index des 3D-Sicherheitsfaktors kartografiert. Unter der Annahme, dass der erste Rutsch der untere Teil eines Ellipsoiden ist, wird die 3D kritische Schlupfoberfläche in der 3D-Böschungsstabilitätsanalyse mit einer Minimierung des 3D-Sicherheitsfaktors mit der Monte Carlo Zufallssimulation erhalten. Die Fehlerwahrscheinlichkeit des Erdrutschs wird mit einer Annäherungsmethode berechnet, bei der die Verteilungen von f,c und dem 3D-Sicherheitsfaktor als innerhalb normaler Verteilungen angenommen werden. Die Beurteilung der Erdbeben-ausgelösten Erdrutschgefahr wird mit der dynamischen Verdrängungsanalyse mit dem Index der Newmark-Verdrängung gearbeitet. Alle Berechnungen werden mit einem Berechnungssystem mit der Bezeichnung 3DSLOPEGIS ausgeführt, bei dem eine GIS-Komponente zum Erfüllen der GIS räumlichen Analysefunktion verwendet wird. Neben der Ergebnissen des 3D-Sicherheitsfaktors und der Wahrscheinlichkeit kann der mögliche Erdrutschkörper und der Umfang dreidimensional quantitativ identifiziert werden.

Jan 1, 2003

By A. Pellegrino, F. Collin, C. Guiducci, R. Charlier

A numerical approach for modeling coupled Hydro-Mechanical fracture behavior in 2D is presented in this paper. This approach accounts for the strong dependence of the flow characteristics on fracture apertures and offers an anisotropic description of the flow propagation in the fracture. An interface finite element and a constitutive model are developed . In order to validate the applicability of the model to general geomechanic problems, 2D simulations were performed. Results show the good application of the mathematical model and the fundamental hydraulic role played by the fractures. In diesem Beitrag wird ein Stoffgesetz vorgeschlagen um hydromechanisches Kluftverhalten numerisch zu Modellieren. Dieser Vorgang nimmt die starke Abhängigkeit der Fliesseigenschaften von der Kluftöffnung mit in Anbetracht. Ein Interfaceelement und ein Stoffgesetz wurden entwickelt. Zum validieren der Anwendbarkeit dieses Modells wurden 2D Simulationen durchgeführt. Ergebnisse haben gezeigt dass das mathematische Model anwendbar ist und dass Klüfte eine fundamentale hydraulische Rolle spielen. Une approche numérique pour la modélisation du comportement couplé hydro-mécanique des fractures en 2D est présentée dans ce papier. Cette approche prend en compte la forte dépendance des caractéristiques du flux de fluide sur les ouvertures des fractures et présente une description anisotrope de la propagation du flux dans la fracture. Un élément fini d'interface et un modèle constitutif sont développés. Dans le but de valider l'applicabilité du modèle à des problèmes généraux de géomécanique, des simulations 2D ont été réalisées. Les résultats montrent la bonne application du modèle mathématique et le rôle hydraulique fondamental joué par les fractures.

Jan 1, 2003

By S. Zhao, S. P. He, M. Y. Zhu, Y. Tao

"The effect of two refining slags (A: 1.0–1.8 CaO/Al2O3 ratio, 11–20 wt% SiO2; and B: 1.0–1.2 CaO/SiO2 ratio, 25–35 wt% Al2O3) on the inclusion morphology of a carbon structural steel (Q235B) was studied by controlling the balance between the steel and the refining slag at 1600ºC in a Si–Mo resistance laboratory furnace. The results showed that most of the inclusions in the molten steel balanced with slag A were formed by a lowmelting CaO–MgO–Al2O3–SiO2 system with a total oxygen content (T[O]) being fixed at 6–13 ppm. The inclusions in liquid steel balanced with the slag B were mostly formed by the CaO–MnO–Al2O3–SiO2 system, with T[O] controlled to 19–26 ppm. The overall size of the inclusions under balance conditions was higher in the steel reacted with the slag B than that reacted with slag A, with the latter showing more inclusions smaller than 3 um. In order to generate a large number of spherical CaO–MgO–Al2O3–SiO2 inclusions smaller than 3 ??m while decreasing the T[O] in the resulting steel, the composition of slag A should be used. This composition allowed improving the cleanliness of the slab, and is also advantageous for the castability of the molten steel. IntroductionThe sample used in this study was a typical carbon steel manufactured by CQ Steel. The galvanized, tinned, and plastic composite steel plates made of the original plates are used extensively for decorative panels, general dust pipes, drums, instrument cases, switchboxes, and train cars, among other uses. The target control composition is shown in Table I. The S and P contents are usually fixed during production below 0.020 and 0.025 wt%, respectively, with the aim of reducing longitudinal cracks on the slab surface."

Jan 1, 2017

By E. L. Thyse

Keywords: Pyrometallurgy, converter, nickel, matte, distribution Metallic elements occupy a wide range in granulated nickel converter matte phases. The distribution of these metallic elements, particularly during crystallization path events, appears to be poorly understood. The present study serves to investigate the distribution of Fe, Co, Ni, Cu, and Pb between nickel-sulphide, copper-sulphide, and alloy phases. A novel combination of thermo-chemical modelling, electron microscopy, and electron probe microanalysis was applied to understand crystallization path events and the associated metallic element distribution. This study has demonstrated that major Ni incorporated during copper-sulphide crystallization would serve to mobilize minor Co towards distribution in copper-sulphide phases. In addition, solid solution substitution of Cu by Ni is manifested by compositional zoning of copper-sulphide phases. The role played by Ni during alloy crystallization suggests that minor Co was also mobilized, along with an increase in principal Ni. Fe, by contrast, seems to be incompatible with principal Ni. In addition, solid solution substitution of Ni with PGEs and Cu is manifested by compositional zoning of NiCu-alloy phases.

Jan 1, 2011

By J. Krzyzanowska

Paper written on project work carried out in partial fulfilment of Bachelor of Engineering-Mining Venetia Mine, an open-pit diamond mining operation in the Limpopo Province of South Africa, currently has a mixed haul truck fleet consisting of Caterpillar 785B and C; 789C; modified 793D and 793D. Even in an ideal situation these trucks have different cycle times, which causes queuing at the loading area and their different speeds cause bunching on the ramps, leading to higher overall cycle times and lower productivity. This problem was identified but the root causes of the problem were not investigated and quantified. A time and motion study on the haul trucks was thus undertaken to measure actual cycle times and compare them to ideal cycle times as well as to observe any reasons for deviations. Ideal cycle times are partly evaluated on the basis of simulation and partly from production optimization expert input. Several areas that affect production were identified and these include: haul road conditions, the control room, dispatching programme and dispatching data management, as well as truck-shovel matching. The investigation was important in establishing control parameters for haul fleet operation since time spent queuing is production time lost, which defers waste tonnes to later in the life of mine, thus decreasing the tempo at which kimberlite is exposed.

Jan 1, 2007

By B. van Beek, J. Ndlovu, K. T. Hara, J. M. A. Geldenhuis

This paper describes the development of an alternative technique for measuring the matte level height in sulphide smelting furnaces. The initial studies involved applying electrochemical oxygen probes in a smelting furnace to measure the oxygen potentials of the matte and slag phases. However, these measurements were not successful as a result of low temperatures, preventing there ference electrode from attaining equilibrium during the measurements. These trials were followed up by using oxygen probes containing a (Mo + MoO2) reference electrode instead of the(Cr + Cr2O3) reference electrode used previously. It was shown that with some further development work, it should be possible to measure the oxygen potential of these mattes accurately. Further measurements were performed with a magnetic sensor in sulphide mattes. It was shown that an electronic signal, which is proportional to the magnetic susceptibility of the surrounding material, was generated during immersion into liquid matte. These measurements were extended and done in a smelting furnace. Initial results indicated that when the magnetic sensor was dipped through the slag layer into the matte, a signal was generated as soon as the sensor came in contact with the matte. Measurements are ongoing in order to record (on a computer for improved accuracy) the signal as a function of distance when the sensor is immersed through the slag layer into the matte phase. The magnetic sensor measurements may be the solution to a matte level measurement problem that has existed for a few decades in matte smelting furnaces.

Jan 1, 2004

A Special General Meeting of the Institute was held in Kelvin House, Johannesburg on Wednesday, 29th September, 1971. The President, Prof. D. D. Howat opened the meeting at 9.55 a.m. The President read the notice of meeting which was as follows: "In order to bring industry into closer liaison with the work of your Institute and to place the Institute's finances on a sound basis your Council recommends that companies be admitted to membership of the Institute under clause 2.6 of the Constitution, that is, as Non-Corporate members. The designation for this class of member will be that of "Company Affiliate". 2 Membership: This clause to be amended as follows:- 2.6 "Non-Corporate members shall comprise the grades of:- Company Affiliate Honorary Fellow Graduate Associate Student" 2.6.1 This clause to be added:- "Companies involved in or associated with the mining or metallurgical industries are eligible to become company affiliates" 2.14 Add:- "A special certificate shall be issued to all company affiliates". After giving the background to the recommendation made by Council the President asked for a proposer and seconder for the resolution. Mr J. K. E. Douglas proposed and Mr D. G. Maxwell seconded the resolution. The meeting agreed that the constitution be amended as proposed. The meeting closed as 10.05 a.m.

By B. Simser

At Brunswick Mine, an increase in the number of seismically-related falls of ground and in particular rockbursts occurred during 1999. This was due to the ever-increasing stress levels in the remaining ore reserves, mining in difficult highly stressed areas and in particular troublesome geological features. In conjunction with the Noranda Technology Centre, development of rockburst support systems started at the Brunswick Mine in 1996 and efforts were accelerated in 1999. A support package consisting of #6 gauge chain link mesh, #0 gauge heavy mesh straps, and a 1 m by 1 m pattern of modified conebolts was developed. The conebolts were modified to enable mixing of the resin anchoring. Two major rockbursts occurred during an intense seismic episode at the Brunswick Mine from October 13th to 17th , 2000.The area was evacuated approximately four hours before the first burst hit, and remained closed during the seismic ?flurry??. The first damaging activity occurred around midnight on Friday the 13th, and a second damaging episode occurred on the 17th that included a local Richter Magnitude 2.7 event. The second rockburst had dimensions of approximately 5 m by 5 m by 20 m or 2150 tonnes of massive sulphide material (density 4300 kg/m3). The first failure area was more extensive, caving approximately six metres of an intersection back with the lateral extent not safely measurable. This paper briefly describes the mining conditions that led to the bursting, the seismic response of the region, the mechanisms thought to have caused the bursts, and a yielding support system which had been partially installed before the burst.

Jan 1, 2002

By M. du Plessis

This paper describes the evaluation of a limit equilibrium model to simulate the behaviour of crush pillars in platinum mines. An analytical model was derived to calculate the residual average pillar stress (APS) values of the crush pillars. The values predicted by this model were compared to the numerical values obtained from TEXAN simulations. In general, the limit equilibrium model appears to be very attractive for simulating pillar failure as the gradual crushing of the outside of the pillar and the transfer of stress to the intact core can be replicated. The value of the TEXAN crush pillar model was further demonstrated by simulating an idealized layout with crush pillars between two adjacent panels. The simulations illustrated that oversized pillars will not crush close to the face and this may lead to seismic failure in the back area. An important finding of the study is that closure measurements may prove to be a very valuable diagnostic measure in crush pillars layouts. Distinct differences in magnitudes of closure were simulated for a scenario where the pillars crush as expected, compared to the scenario where an oversized pillar is left. Experimental closure data collected in a crush pillar stope provided further evidence regarding the value of closure measurements in these layouts.

Jan 1, 2011

By B. P. Watson

The first crush pillars on the Bushveld platinum mines were introduced at Union Section in 1978. Before the introduction of crush pillars, serious problems were experienced when stoping advanced to a point 30 m to 40 m on both sides of the centre gully. At least three to four stopes were collapsing per month. The introduction of the pillars stopped the stope collapses in the mining area where they were introduced. The residual stresses of these pillars were never measured; however, the successful elimination of the ?back-break? problem suggests that the original pillars had a residual strength of at least 8 MPa. Apart from back analyses, very little work has been done to determine the residual strength of crush pillars and only very recently have any measurements been made. The lack of knowledge in this field has resulted in pillars being designed based on experience. Concerns about stope collapses, similar to the Coalbrook disaster, have led to larger pillars being cut in more recent times. If such pillars were cut in brittle quartzites they would always fail violently but the ductile nature of the Merensky Reef generally allows large pillars to fail without bursting. Occasionally, however, one would burst in a working area. Increased incidence of bursting has been reported on some mines at deeper levels but most of these bursts occur in the back areas. Nevertheless, the incidence of bursting increases the risk of falls of ground in already dangerous areas, and the larger pillars decrease the extraction ratio. This paper describes the evaluation of stress measurements conducted in two boreholes over a crush pillar with dimensions 2.5 m x4.0 m, and a height of 1.2 m. Boussinesq equations for vertical and shear stress were used to analyse the original measurements and provide a stress profile across the pillar as well as the residual strength of the pillar. The results showed an unexpectedly high peak stress of 280 MPa at the centre of the pillar and a residual strength of 48 MPa. The reason for the high residual strength is suspected to be the result of the stiff environment under which the pillar failed and the small height of the siding on the up-dip edge of the pillar. More measurements should be conducted on several mines to establish a range of residual strengths for narrow crush pillars.

Jan 1, 2008

By J. H. Rhee, H. B. Ku, J. S. Lee, H. J. Park, B. S. Jang

A large wedge failure had occurred in the study area which was under construction. Therefore, in order to analyze the potential instability for this rock slope, the authors conducted numerical analysis with DEM and then the behaviour of rock mass was analysed after appropriate reinforce-ments were applied. Ein großer Keildefekt geschah in dem Untersuchungsgebiet, das im Bau befindlich ist. Deshalb, um die potentielle Unbeständigkeit für diesen Felsenabhang zu analysieren, führen die Urheber zahlenmäßige Analyse mit DEM. Und dann wird die Bewegung der Felsenmasse ana-lysiert, nachdem angemessene Verstärkungstruppen angewandt werden. Un grand échec de coin sèst passé dans le région étudié qui était en construction. Par conséquent afin d’analyser linstabilité potentielle de cette pente de roches, les auteurs ont mené une analyse numérique avec DEM. Ensuite le comportement de la masse de roches pourrait être analysée après les renforts appropriés étaient appliqués.

Jan 1, 2003

By H. E. James

Much has been said and written about the need to reduce South Africa's dependence on gold. To compensate for the decline in the country's foreign-exchange earnings resulting from the phasing out of gold, which must inevitably occur at some future date, a far higher priority will have to be placed on the mining, beneficiation, and export of the 59 other mineral commodities produced in South Africa. The basic strategy of the mining and metallurgical industries should be to move from the traditional approach of establishing a resource base to the establishment of a market base; to turn from production orientation to market orientation; and to rely less on exploration and economies of scale and more on process innovation and product development. The enthusiasm, entrepreneurial spirit, and commitment of the leaders in the mining and metallurgical industry will clearly be of decisive importance in the establishment of new industries for the beneficiation and export of added-value mineral-based products. The State can make a significant contribution by the provision of a welldeveloped and efficient infrastructure, including rail and harbour facilities, communications and health services, roads, and of electricity and water supplies. In our search for a new development strategy for the beneficiation and export of South Africa's minerals, we need to recognize that no one nation has all the mineralresources that it needs. Commercial and strategic manipulation of mineral supplies should no longer be tolerated. The future of the human species lies in international cooperation and in a greater understanding of the limitations of the world we live in.

Jan 1, 1985

The optimum cut-off grade policy maximizes the net present value (NPV) of an open pit mining operation subject to the mining, processing, and refining capacity constraints. The traditional approaches to cut-off grade determination ignore the escalation of the economic parameters such as metal price and operating costs during life of an operation, and consequently lead to unrealistically higher values of the objective function. Further, the NPV of a mining operation declines due to the depletion of the available reserves, causing a decline in the optimum cut-off grade, i.e. higher cut-off grades in the early years of an operation and lower cut-off grades during the later years. Hence, low grade material mined in the earlier years may be stockpiled for processing during later years to offset the effect of escalating economic parameters on NPV. This paper demonstrates the combined impact of introducing economic parameters, escalation and stockpiling options into the cut-off grade optimization model. The model promises an enhancement in NPV as illustrated in a case study incorporating practical aspects of an open pit mining operation.

Jan 1, 2011

By D. J. Fourie

During the production of pure TiO2for the pigment industry, ilmenite, containing 35?60% TiO2, is reduced to high titania slag, containing 70?95% ?TiO2? and pig iron. The high titania slag produced, consists mainly of titanium in different oxidation states and FeO in equilibrium with liquid iron. To predict the phase and chemical reaction equilibria in a furnace, a suitable solution model is required with accurately determined binary interaction parameters, as slag melts tend to behave very non-ideally. This paper investigates two popular slag models, namely, modified quasi-Chemical (MQC) model and the cell model and provides the binary interaction parameters based on recently published data of the ternary system and critically assessed published unary and binary data. Very few modelling results have been published on the ternary Ti-Fe-O system pertaining to high titanium slags. The solution models, with their regressed interaction parameters, can subsequently be implemented in commercial software of the slag-metal phase equilibria to predict how much and which type of solids will precipitate for a given bulk slag chemistry and operating temperature or, alternatively, above which temperature should a furnace be operated to avoid excessive solids precipitation.

Jan 1, 2005

By J. N. Van der Merwe

"A major shortcoming of the statistical back-analysis of coal pillar strength is that it relies on the asmined pillar dimensions, not taking into account time-related pillar scaling with subsequent reduction in pillar width. The paper describes an investigation where the rate of pillar scaling was applied to the pillars in the databases of failed and unfailed pillars. The reduced pillar sizes were then used in the same method of statistical back-analysis that had been used in the past.This resulted in an equation for pillar strength which predicts significantly greater pillar strength than the previous statistical analyses, which is similar to the strength which had been found earlier by direct testing of large specimens underground. It is concluded that the lower strengths found by previous statistical analyses are due to the incorrect pillar width being used and that by adjusting the pillar sizes to compensate for scaling, more credible results that correspond to direct testing are obtained.As the newly derived strength equation is time-dependent, it follows that the safety factors and probabilities of failure are likewise time-dependant. An equation to determine the probability of failure is also developed. This results in the safety factor being close to unity at a probability of failure of 50%, which is aligned to statistical expectation. IntroductionSince the Coalbrook mine disaster, caused by massive pillar collapse, there have been several attempts at analysing and defining the strength of coal pillars. It was realized in the very beginning that performing classical strength tests on coal specimens in a laboratory and then transferring those results to real coal pillars could not be successful. The scatter of results is one problem and, more seriously, there is a size effect (at least for small specimens) that made the transformation of strength results to much larger coal pillars underground all but impossible.Two main schools of thought then emerged. Some researchers preferred to perform direct strength tests on large specimens underground, while others relied on statistical back-analysis of failed and unfailed pillar cases, attempting to determine the differences in size and shape that would allow a satisfactory prediction of failure. The latter school of thought resulted in the method that was widely accepted by the South African coal mining industry, described in the landmark publication by Salamon and Munro (1967)."

Jul 1, 2019

By W. Wittke, J. Gattermann

ABSTRACT: One alternative to close a radioactive waste repository in rock salt is the construction of a “Cross Section Closure (CSC)“ sealing barrier. The proposed material for the CSC is highly compacted bentonite. To investigate the swelling behaviour of a highly compacted bentonite a large number of laboratory tests were performed. In addition, large scale model test were carried out to demonstrate the development of a nearly homogeneous and isotropic swelling pressure. The results of the large scale model tests were interpreted numerically based on the models for stress-strain behaviour and water uptake which are implemented in the finite element codes FEST03 and HYDOPO. The investigations show a good agreement of the results of the model tests and the corresponding analyses and show, that the theoretical models are capable of describing the behaviour of sealing structures based on highly compacted bentonite. ZUSAMMENFASSUNG: Eine Möglichkeit für den Verschluß eines Endlagers für radioaktive Abfälle im Steinsalz ist die Konstruktion einer Querschnittsabdichtung aus hochverdichtetem Bentonit. Zur Untersuchung des Quellverhaltens von hochverdichtetem Bentonit wurden eine große Anzahl von Laborversuchen durchgeführt. Um die Entwicklung eines nahezu homogenen und isotropen Quelldrucks nachzuweisen, wurden darüber hinaus auch Modellversuche in größerem Maßstab durchgeführt. Die Ergebnisse dieser Modellversuche wurden im Hinblick auf die Wasseraufnahme und das Spannungs-Verformungsverhalten mit Hilfe numerischer Berechnungen mit den finite Element Programmen FEST 03 und HYDOPO interpretiert. Die Untersuchungen zeigen gute Übereinstimmungen zwischen Versuchs- und Berechnungsergebnissen. Die numerischen Modelle sind somit geeignet, das Verhalten von Abdichtungsbauwerken aus hochverdichtetem Bentonit zutreffend zu beschreiben. RÉSUMÉ: Une possibilité pour fermer un dépôt final de déchets radioactifs dans sel gemme est la construction d'un étanchement de coupe transversale, fabriqué de bentonite fortement compacté. Pour étudier le comportement de gonflement de bentonite fortement compacté, de nombreux essais en laboratoire ont été exécutés. En outre, des essais sur modèle sur une plus grande échelle ont aussi été exécutes afin de prouver le développement d'une pression de gonflement à peu près homogène et isotrope. Les résultats de ces essais sur modèle étaient interprétés en vue de l'absorption d'eau et du comportement contraintes-déformations par le moyen de calculs numériques avec les programmes d'éléments finis FEST03 et HYDOPO. Les études montrent de bonnes conformités entre des résultats d'essai et de calcul. Les modèles numériques sont ainsi capables de décrire justement le comportement d'ouvrages d'étanchement fabriqués de bentonite fortement compacté.

Jan 1, 2003

By Lutz Markworth, Wolfram Jaspers, Johannes Kottmann

PNEUFLOT® technology has been applied for the past 20 years in coal, ore and other minerals processing plants. During the last two years this technology has achieved a breakthrough with some 42 units being sold signifying a rising trend. »Humboldt Wedag Coal & Minerals Technology« has performed extensive research and development work over the last five years. The results of which were used to design a new fourth generation aerator. Humboldt Wedag, through its association with EKOF, can offer a holistic solution encompassing both flotation equipment and reagents. It is the only company in the world able to offer such a package. The association with EKOF strengthens the Humboldt Wedag product offering, especially as the company in-troduced pneumatic flotation cells to the South African market in the form of the PNEUFLOT®. Before starting pilot scale test work, a mineralogical analysis has to be carried out to determine the mineral com-position as well as the liberation grade. HW-CMT works together with independent institutes. Different reagent regimes can be tested in laboratory scale. Pilot machines, each packed in a 20? container, are available to carry out extensive test work at customers? processing plants. A group of engineers from HW-CMT is involved in the pilot test work. The flexible pilot machines are designed to cater for coal, ores and other minerals. The small feed rates of 7 ? 12 m³/h only means the pilot machines do not disturb the operation of process plants. Batch tests have to be carried out to determine the numbers of PNEU-FLOT® stages. New applications in iron ore, copper ore, platinum group minerals, rock phosphate and potash were suc-cessfully tested in the last three years. In applications where the feed material is very fine, PNEUFLOT® technology is able to achieve high recoveries with particle sizes where conventional technology failed.

Jan 1, 2007

By H. Hurkchand

Background: A cross-sectional study was conducted in November2001 to establish the prevalence rates of Human Immunodeficiency Virus (HIV) and sexually transmitted infections (STIs) (Chlamydia trachomatis and Neisseria gonorrhoea) in a coalmining town in Mpumalanga. Methods: 155 adults were recruited (79 males and 76 females), by holding community meetings, and by door-to-door recruitment. Saliva and urine specimens were collected for the analysis of HIV and STI prevalence, respectively. Results: The mean age for males was 31.35 years (min = 19 yrs and max = 50 yrs) and the mean age of the female participants was31.90 years (min = 17 yrs, max = 49 yrs). The prevalence of HIV was found to be 22.78% [95% CI (14.09?33.59)] in the males vs. 47.37%[95% CI (35.79?55.16)] in the females, [p = 0.001, OR = 3.05, 95%CI(1.49?6.26)]. The prevalence of C. trachomatis was 7.90% [95% CI(2.95?16.39)] in the males vs. 12.86% [95% CI (6.05?23.00)] in the females, p = 0.324. The prevalence of N. gonorrhoea was 3.79%[95% CI (0.79?1.08)] in the males vs. 9.86% [95% CI (4.06?19.26)]in the females, p = 0.137. HIV was significantly associated with C. trachomatis, [p = 0.032, OR = 3.18, 95% CI (1.04?9.72)], but was not significant when stratified by gender. HIV was not significantly associated with N. gonorrhoea (p = 0.072) but it was significantly associated when stratified by gender, p = 0.001 for females. There were no significant associations between HIV and age (p = 0.408), even upon stratification by gender. Conclusions: HIV prevalence in this community is high, and corresponds to national figures. However, the prevalence of STIs is surprisingly low as it would be expected to be high in a migrant population. Although communities are exposed to expanding peer-education activities that encourage behaviour change, the prevalence of HIV in this group. There is an urgent need for interventions designed to treat or prevent HIV infection in women generally and in women at high risk. Keywords: HIV prevalence, STI prevalence, antenatal, mining

Jan 1, 2005