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By J. Nielen van der Merwe

For the last 3 decades, coal pillars in the Republic of South Africa have been designed using the well-known strength formula of Salamon and Munro that was empirically derived after the Coalbrook disaster. The database was recently updated with the addition of failures that occurred after the initial analysis and the omission of failures that occurred in a known anomalous area. An alternative method of analysis was used to refine the constants in the formula. The outcome was a new formula that shows that the larger width-to-height ratio coal pillars are significantly stronger than previously believed, even though the material itself is represented by a reduced constant in the new formula. The formula predicts lower strength for the smaller pillars, explaining the failure of small pillars that were previously believed to have had high safety factors. Application of the new formula will result in improved coal reserve utilization for deeper workings and enhanced stability of shallow workings.

Jan 5, 1999

A good blasting result is largely achieved by putting the right amount of explosive in the right place and firing it in the right sequence. The best blast design in the world will not break the rock if the planned blast layout is not achieved in the field. One of the critical inputs into a blast design is the diameter of the blasthole. An assumption that the actual blasthole diameter is equal to the nominal drill bit size is generally made. However, a small deviation in the actual hole diameter from that assumed will have a dramatic effect on the hole's volume and, consequently, where the explosive is placed in the blasthole. Any discrepancy in actual blasthole volume from that assumed will be reflected in 'overloading' or 'underloading' of the blasthole with the calculated explosive quantity and, thus, reflect in explosive distribution and stemming lengths. When loading to a 'collar' in an oversized hole extra explosive will be used, resulting in higher than planned powder factors and explosive costs. A blasthole diameter assumed from a nominal drill bit size is an incorrect assumption. This paper will present some actual blasthole diameter measurements illustrating the variation in hole diameters seen in the field and proposes a practical method for achieving a useful blasthole diameter measurement.

Jan 1, 1990

By Liqun Liang

Various nondestructive testing (NDT) inspection methods are available to evaluate the structural integrity of cast-in-place shafts. The widely used methods include Cross Hole Sonic Logging Testing and Low Strain Testing. Due to its advantages such as low cost, easy operation, quickness and flexibility (no need to plan ahead and prepare inspection tubes or other devices), Low Strain Test is frequently specified in quality assurance programs of many countries or when doubts arise as to the integrity of the finished shafts/piles. The method is well suited for small to middle sized shafts. However it is an indirect NDT testing method and has certain limitations. Data interpretation requires proper training, experience and judgment and, therefore, inconsistent conclusions and reporting may be provided by different testers. To avoid or reduce such inconsistencies, it is best to follow a standardized data interpretation and record classification system. In this paper, a new classification method is presented with examples. A step-by-step data evaluation and interpretation procedure is proposed with examples of real cases to help understand the LST data. The paper also makes recommendations for measures to be taken when anomalies are detected in tested production piles.

Jan 1, 2011

By Edward A. Barrett, Lynn L. Rethi

From 1987 through 1996, 13 fatalities occurred at underground operations in the U.S. stone mining industry. A review of the underground limestone mine industry data for this 10 year period indicated a high fatality concentration in one area: ground failures.

By Mark S. Stagg, Rolfe E. Otterness, Farrokh Djahanguiri

The U.S. Bureau of Mines (USBM) evaluated empirical equations that predict fragmentation from underground stope rounds. Controlled blasting is necessary for creating leaching stopes that maximize the recovery and minimize backbreak of the perimeter wall. This paper presents the fragmentation results from one of the three drop-raise blasts used to develop a reduced-scale cylindrical stope, 1.8 m in diameter and 6 m in height. The stope is located in the Colorado School of Mines Experimental Mine (Edgar Mine) in Idaho Springs, Colorado. This stope is part of a USBM research effort to determine the feasibility of incorporating in situ leaching of rubblized stopes into active underground metal and nonmetal mines.

Jan 1, 1994

By Carls Benedicks

It is well known by every one who has had to deal with boiler tubes that these are often seriously affected by a sort of corrosion, occurring as a local pitting, that frequently causes a perforation of the tube in a rather short time. The characteristic appearance of this corrosion is shown in Fig. 1. A very similar corrosion occurs in condenser tubes (Fig. 2).l A study of the microstructure or local chemical composition of the metal (iron 70:30 brass) fails to reveal any cause for this pitting. Of course one might possibly assume the starting point to be some oxide particle, causing an electrolytic local action, but this in no way explains the continued corrosion, progressing even when the assumed oxide particle must have disappeared. By the excellent work done by the Corrosion Research Committee of the Institute of Metals, and communicated, in October, 1923, to the Institution of Engineers and Shipbuilders in Newcastle-on-tyne, stress was laid on the faot that a content of entangled air has a very obnoxious effect. In the following correspondence, Sir George Goodwin stated that "engineers have, for a long time past, regarded air as the big enemy to be fought against in all questions of corrosion'72 and Kenneth Fraser pointed out that the most vital point is "the avoidance or removal of possibly the chief cause of present day corrosion, i. e. entrapped air and gases brought out of solution."3 In their reply, however, the authors state that they had "never for a moment believed that entangled air was responsible for the beginnings of corrosion, and express the opinion that the gradual liberation of air could not account for localized corro~ion."~ On consulting the many textbooks on corrosion, as that

Jan 1, 1925

By A. B. Wilder

We study the past Because it is a guide to the present and a promise for the future. The struggle for a better world is strengthened By the hopes, ambitions, and deeds Of those who were before us. As we look backward Our attention is directed forward. ONE hundred years ago, the manufacture of steel from molten pig iron without the use of fuel first began. In the earlier part of the nineteenth century the crucible process was the principal steelmaking method. It was a costly process, producing only a few pounds of steel at a time; so, most of the ferrous metal output was in the form of wrought or pig iron. With the perfection of the converter technique it became possible to produce low cost steel by the ton, thereby completely changing the structure, not only of the ferrous metal industry, but also of industrial production in general. This was the turning point from the Iron Age to the Age of Steel. William Kelly (Fig. 2), Sir Henry Bessemer (Fig. 1), and Joseph G. Martien experimented with the process before 1856. William Kelly began in Eddyville, Ky., in 1847 and has been given credit for first discovering the principle of the pneumatic converter process. Several years later in England Henry Bessemer independently conceived a steelmaking process similar to Kelly's. Bessemer made public his invention at the annual meeting of the British Association for the Advancement of Science held at Cheltenham, England, August 1856. As a result of his paper, "On the Manufacture of Malleable Iron and Steel Without Fuel," and his progressive leadership in the years to follow, the process became permanently identified with the name, Bessemer. Credit for the commercial adaptation of the process must be given two additional persons. Robert Mushet (Fig. 3) in 1856 in England recognized the necessity of deoxidation and recarburization of the converter product and evolved the technique for adding high manganese iron following the blow. In Sweden, in July 1858, G_ F. Göranson [ ]

Jan 1, 1961

In the first half of this century a mining industry was developed in Indonesia under Dutch colonial rule. World War II and the subsequent struggle for independence resulted in the destruction of most of the infras- tructure and much of the data. After independence, restrictions on for- eign investment and internal turmoil prevented re-establishment of a viable mining industry until the formation of the present Government after 1965 and the enactment of sound laws in 1967 to encourage foreign investment. Rebirth of the mining industry was followed initially by slow growth, but in the 1980's, spurred by the worldwide interest in gold, Indonesia has become the focus of an intense exploration boom for gold and other precious metals. 103 Contracts of Work for gold have been awarded since 1985 with Australian companies being the most predominant. Since 1985 three new gold operations have been commissioned and another two are nearing completion. Several more are undergoing feasi- bility studies. There is reason to predict that Indonesian gold produc- tion will grow to place the country in the ranks of significant producers during the 1990's.

Jan 1, 1988

By Jouko L. Lehtonen

Sheet pile walls can be sealed watertightly using various methods. The objective of this paper is to introduce a new innovation comprising the use of continuous cement grouting during embedding. The method has been tested on a field test site and installation and permeability features have been observed and analyzed. Installation can be carried out using traditional sheet piling machinery, merely some additional grouting equipment is needed. Installation speed of grouted sheet piles corresponds to that of conventional embedding. The permeability of the tested method is satisfactory in applications where e.g. polluted soil or water has to be isolated from the surrounding environment. In addition, this method can be used for conventional retaining walls where very low permeability is required or for reduction of soil vibration, e.g. close to a railway embankment. The new method to grout simultaneously and continuously during embedding has been developed based on respective innovations on impact driven steel piles.

Jan 1, 2006

By J. F. T. Agapito

Stability in Exxon's Colony Pilot Mine in the Piceance Creek Basin, Colorado has been monitored by periodic pillar stress-determinations End roof-to-floor convergence measurements since 1971. Pillar failure has caused marginal stability in some areas of the mine. Measurements taken during the process of failure provided valuable information on the in-situ pillar strength and long-term behavior of the mine structure. Four pillars were reinforced by 32 mm (1-1/4 in) diameter tensioned grouted bolts to increase long-term stability in the northern area of the mine. Stability of this area is necessary because future plans envision its use as an exit/access and ventilation exhaust. Computer analyses were performed to help evaluate the effect of pillar reinforcement on long-term stability. Results indicate that bolting is particularly useful in stabilizing failed pillars, but its effects are significant only in the immediate area of the pillar. The projected significant decrease in deformation of two extensively failed pillars near a main entry indicates that bolting reinforcement will assist the long-term stability of the opening.

Jan 1, 1985

By H. W. Kerr, B. Soutiere

THE possibility of using unidirectionally solidified eutectic alloys as high-strength composite materials has been investigated by several workers. Unidirectionally solidified lamellar and fibrous eutectics have been shown to have good short-time structural stability at temperatures close to the eutectic melting temperature.'-4 Several investigations of both short-time high temperature tensile properties and creep properties of eutectic alloys have been carried out,3-" with promising results. Little work has been reported, however, on the thermal stability of eutectic alloys which have been unidirectionally solidified and subsequently deformed in compression. Since processes such as rolling and grinding introduce compressive stresses, and since the properties depend on the spacing and perfection of the composite structure10,11 this aspect is of definite importance if unidirectionally solidified eutectic alloys are to be considered for commercial use. A Cd-Zn alloy made from 99.999 pct starting materials was cast into a graphite boat and zone levelled12 to obtain a completely lamellar structure at one end of the bar. Sections from this region of the bar were removed, recast into 6.5 mm I.D. Pyrex tubing, and solidified unidirectionally upwards at a rate of 2.8 cm per hr. Specimens were cut from the solidified rods, heated in air at 200°C (0.88 of the eutectic melting temperature) for various lengths of time, and examined metal-lographically. Compression specimens were also cut from the solidified rod carefully machined to a length of & in., and deformed with the compressive axis parallel to the original growth axis to produce a total longitudinal strain of 12 pct. Some of these specimens were examined metallographically; others were heated in air at 200°C for various lengths of time and then examined. Metallographic examination of the deformed specimens showed the two types of deformation previously described; slip lines13 (smoothly bent lamellae) and kinks13,14 (sharply bent lamellae). Very close to the specimen ends there were a large number of deformation bands, but at a distance of about -re- in. the deformation was very localized, as shown in Fig. 1.

Jan 1, 1970

By D. F. Hewett

ALTHOUGH most persons will agree that an individual or a nation can profit from the experience of other individuals or nations, there is always room for debate over the degree of similarity of their past and present conditions and of their future problems. Noting the increasing interest that Americans are showing in our mineral problems, I have felt that we could profit from reviews of the experiences in mineral exploitation acquired by the industrial nations of Europe. Whether we can learn much from Europe's experience in exploiting such minerals as petroleum may be debatable, but certainly, with a record of metal production extending back nearly 3000 years, Europe should hold much of value for America. A trip to Europe in 1926 permitted me to visit 28 mining districts, of which about half are now or have been in times past outstanding sources of several metals. The districts range from England to Greece and from Spain to Poland. To summarize briefly my impressions of these mining districts, as well as such reactions to the thought and life of Europe as so short a visit permits, I shall only venture the opinion that Americans can review with great profit the ideas and actions of Europeans, with regard not only to the production of metals but to many expressions of life. I believe that America has made and is making new contributions to the art of living, as well as to the arts of mining and metallurgy, but in so far as Europe is and has been a laboratory of economic, social and political experiments, the results she has attained deserve the thoughtful attention of America. I have come to believe that many of the problems that harass Europe lie in our path not far ahead. I have therefore hoped that a review of metal production in Europe in the light of its geologic, economic and political background may -serve to clear our vision with regard to our own metal production.

Jan 1, 1929

The paper reviews some characteristic features of feasibility studies and discusses the need for a wide scope at the pre-feasibility stage. The performance of recent Australian gold mines against the predictions contained in their respective feasibility studies is examined, resulting in a recommendation that feasibility studies need to be improved The advantages to be gained from having a feasibility study reviewed by an independent authority are discussed, and some of the reasons for using consultants are listed. Two examples of successful optimisations in the early stages of pre-development studies are described briefly and the benefits achieved are presented. The paper concludes that feasibility studies need improvement to enhance the confidence of investors in the mining industry.

Jan 1, 1991

By J. P. Cooney

Placer Dome is learning from experience in Latin America, Asia and Africa, as well as in North America, that contributing effectively to sustainable human progress in the areas of its operations presents unending challenges to think creatively, communicate effectively and remain culturally sensitive. People must be better off in terms of their economic circumstances, their social conditions and the quality of their natural environment not only during the life of the mines, but after mines close. Stakeholders, all those who are directly or indirectly affected by a mining project, should be able to participate in decisions which affect them. The development of sustainability strategies, the monitoring of sustainability performance and the implementation of sustainability programs are best done in partnerships with governments, communities, nongovernmental organizations and multilateral development institutions. Ultimately, the success, if not the survival of mining, will depend on our ability to get the sustainability equation correct.

Jan 1, 2000

By William C. Cassun

The important role of pit slope design in the overall economics of open-pit mining ventures has long been recognized and well documented.1 2 Any economic analysis of a pit slope design must reflect the trade-off between the benefits and the increased risk of slope failure inherent in steeper slope angles. The conventional practice in pit slope design is based on the factor of safety analysis.' The approach uses average values to arrive at a deterministic solution to slope stability. Past analyses based on this approach generally have had several drawbacks: 1. The risk from slope failure could not be quantified. 2. Only relatively simple pit wall geometries were considered. 3. The analyses were performed solely for the benefits of steeper slopes, seldom discussing the potential costs of slope failures. 4. Analyses were seldom considered in a year-by-year mine planning context. Recognizing that average values do not reflect the uncertainty in geomechanical parameters, a probabilistic philosophy to slope design has evolved. 4,5 However, this approach had not been fully developed to include complex slope geometries and mine planning consideration. In order to develop an integrated, pit slope design procedure, a research project was initiated at the University of Arizona during 1973 in conjunction with the Canada Center for Mineral and Energy Teleology. This research resulted in the development of a probabilistic design procedure. The remainder of this paper gives an overview of the probabilistic design procedure and a discussion of the requirements for the benefit-cost analysis of a pit slope design. Finally, the results of a case study undertaken at an operating mine are given.

Jan 1, 1977

By Marzio Piller, Girolamo Belardi, Jure Mencinger, Paolo Bozano, Gianni Schena

"The hydrodynamics of the Tri-Flo™, a two stage cylindrical cyclone used in dense media separation, is studied using Computational Fluid Dynamics. The flow field is simulated with an Euler-Euler Volume of Fluid two-phase approach and the Reynolds stress turbulence model.A unique feature of the device is that the separation medium suspension is pumped and introduced tangentially into the two cylindrical compartments while the raw feed is conveyed to the feed hopper and fed at the axial inlet. This feature allows to use less pumping energy and limits the unavoidable production of fines. The Tri-Flo™ complex flow pattern is little known but central to the efficiency of the separation.The velocity field is computed within the two compartments of the separator. The interface of the air-core that forms in the inner axial part of the cylindrical sections is identified and visualized. The numerical results for a reduced-size 100 mm ID Tri-Flo™ are compared against laser Doppler measurements on a transparent acrylic model (Chinè, 1995) operated with water. The robustness of the model and its prediction capability are verified.The possibility to accurately predict the velocity profiles within the vessel and their dependence on the main Tri-Flo™ operating and geometrical variables paves the way to a better understanding of the functioning of the separator, its design improvements and scale-up."

Jan 1, 2014

By N. R. Sainath

This paper discusses the results of a laboratory investigation carried out to study the microscale flow characteristics of copper ores and the variation in flow behavior resulting from flow of leach solution. Fractures in 1.5 and 4 inch diameter cores were mapped by visual inspection. The cores were stressed in a triaxial stress field representative of in situ conditions. The permeability of the samples to water was then estimated. The samples were exposed to 20 g/l sulfuric acid and the experiment repeated. The Permeability of unleached samples ranges from 10-1 to 10-19 m2 and it increases as leaching progresses. The porosity variation and the rate of recovery of copper from the specimen during leaching were also studied.

Jan 1, 1991

The most important event affecting the United States coal industry in 1993 was the strike by the United Mine Workers of America (UMWA). This was a series of selective strikes, beginning with a strike against four Peabody Holding affiliates on Feb. 2, following unsuccessful contract negotiations between the UMWA and the Bituminous Coal Operators' Association (BCOA). Although that strike ended on March 3, the failure to reach a new contract agreement led to walkouts at several Midwestern mines on May 10. During the summer, the strike expanded to include mines of 13 companies in seven states including Ohio, Pennsylvania, Illinois, Indiana, Kentucky, Virginia and West Virginia. About 17,000 miners were idled during the strike. As the prospects for a settlement diminished, the Secretary of Labor appointed a federal mediator. The mediation resulted in a five-year contract. In addition to increases in wages and pensions, it was agreed that 60% of new job openings would be filled by laid off and active UMWA miners. In return, companies won the right to establish more flexible work rules and scheduling of miners. While some health care benefits were expanded, the agreement established a new health care system that was designed to reduce costs. Preliminary Energy Information Administration (EIA) data indicate that US coal production fell by 5% in 1993, to 859 Mt (947 million st) (Table 1). The strike was one of the primary causes of the decline in production. Another significant cause was a 27% decline in coal exports. Also, a very small displacement of domestic coal production resulted from a rise in coal imports.

Jan 1, 1994

By Henry Hengeveld

Are the IPCC results credible? The most recent IPCC assessment is??an admirable summary of research activities in climate science? US National Academy of Science 2001 report to President Bush Joint statement by Academies of Science from 17 other countries ? May 2001 ?The work of the?IPCC represents the consensus of the international science community on climate change science. We recognize IPCC as the world?s most reliable source of information?and endorse its method of achieving this consensus.?

Nov 1, 2002

By Gustavo A. Munoz

Activated carbons owe their adsorption capacities to their extensively developed pore network structure. As a result, these adsorbents generally exhibit high specific surface areas. Currently, granular activated carbons produced from coconut shells are traditionally used for gold recovery by adsorption from cyanide leaching solutions. Magnetic activated carbons (MACs) for gold recovery from cyanide solutions produced from sources other than coconut shells have been developed at the University of Utah by mixing a magnetic precursor with a carbon source, and treating the mixture under controlled conditions of temperature and gas phase composition. The pore size distribution of the activated carbons is dependent on the degree of activation, among other factors. The significance of the MAC pore size distribution on gold adsorption kinetics and gold adsorption capacity is presented.

Jan 1, 2003