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By Max John

INTRODUCTION One of the main advantages of the New Austrian Tunneling Method (NATM) is its adaptability to varying rock conditions. This method is therefore successfully applied when complex geologic features are expected which cause uncertainties in the prognosis of the rock mass behaviour, as was the care at the Arlberg Expressway Tunnel. Furthermore, by employing the NATM problems are avoided when encountering varying geologic conditions or even extension fault zones along the tunnel, as was the case at the Dalaaser Tunnel and Perjen Tunnel. The NATM can also be used for rock and soil. The following examples will show how various rock conditions can be mastered. In accordance with the NATM all tunnels which will be discussed are road tunnels having a cross section area between 70 and 100 m2. The construction consists of a primary support, which ensures stress redistribution during excavation (Figure 1). The primary support is reinforced shotcrete strengthened by steel arches, when necessary, and rock bolts. When encountering rock pressure, swelling rock or soil, the primary support is suplemented by an invert arch. The purpose of the secondary lining is to increase the safety of the tunnel with regard to long-term stress redistribution processes or changes in rock mass properties as well as to protect the insulation. The secondary lining consists of cast concrete without reinforcement and is generally 0.25 or 0.30 m thick.

Jan 1, 1981

By S. Mathur, Pradip

Polyacrylic acid (PAA) was evaluated as a selective flocculant for the dolomite-apatite system. PAA with a molecular weight (MW) of 4 million was found to flocculate both dolomite and apatite. However, the flocculation behaviors of dolomite and apatite were significantly different with 450,000 MW PAA, which was found to be the lowest molecular weight fraction capable of flocculation. In single-mineral tests with a dosage of 2 kg/t PAA, 90% of the dolomite and 35% of the apatite flocculated. Selectivity was achieved in mixed mineral tests. From a feed consisting of an 80:20 mixture of apatite and dolomite, respectively, a concentrate containing 90% apatite was obtained with a 70% recovery. The dolomite rejection was about 75%, which corresponds to a 2% MgO content in the concentrate.

Jan 1, 1997

By Wai Wu, C. Haycocks

The majority of Appalachian coal deposits lie in a multi-seam environment. Historically, the decision to extract a particular seam has been based on ease of access, ownership and economics rather than ground control considerations. As mining progresses and seams are being mined out, it is increasingly common to find working and abandoned mines in close vertical proximity to each other. Such contiguous operations can produce both positive and negative ground control situations in neighboring seams. These ground control problems, defined as interaction problems, are frequently reported, and their severity can range from minor roof problems that may require no additional support to complete loss of a large section of coal reserves (Stemple, 1955; Peng & Chandra, 1980; Haycocks & Karmis, 1983; Su et al, 1984). As a consequence, interaction problems are of growing concern to the Appalachian underground coal industry. Although interaction problems in multi-seam mining have been recognized for many years and many investigations have been conducted to study the problems, the ground control principles involved in their development are only partially understood. Previous research has identified four interaction mechanisms: pillar load transfer, innerburden shearing, arching effects and upper seam subsidence (Haycocks et al, 1982; Haycocks & Karmis, 1983). Pillar load transfer mechanisms and innerburden shearing have been successfuly used to explain interaction phenomena associated with undermining operations, while arching and subsidence have been used to assess problems during overmining. In addition, interaction-controlling factors such as cover, innerburden and seam thicknesses, extraction percentages on both seams, time delay between operations on two seams, and characteristics of innerburden rock have been identified and utilized in evaluation of interaction effects (Haycocks & Karmis, 1983; Webster et a1.,1984). As an example, Figure 1 shows the relation of innerburden layering and thickness to interaction on the lower seam. The combination of such theoretical work and the analysis of case study information has made it possible to determine, with a certain degree of confidence, the interaction damage in undermining conditions. The results of such an approach have been sufficiently successful and complete to be incorporated into a software package to assist field engineers in estimating potential interaction effects when undermining a previously mined upper seam (Grenoble et al, 1984; Grenoble & Haycocks, 1985; Grenoble et al, 1985). Although the conventional finite element and photoelastic modeling techniques have been

Jan 1, 1986

By J. Hoover

Real growth in the economy, increasing demand for electricity, and consumer stockpiling for a possible United Mineworkers of America (UMW) strike in October made 1984 a banner year for coal. Production and consumption climbed to record heights. Precautionary purchases brought inventories close to the peak levels of early 1981 when coal miners walked out for 72 days. Production slowed in the fourth quarter after labor and management concluded negotiations without a walkout. But output in every major coal producing state showed significant gains during the year US coal production totaled 807 Mt (890 million st) in 1984. This is a 13.8% increase over 1983 output. Lower production rates, principally in Appalachia, and sustained demand in the final quarter put downward pressure on coal stocks by the end of the year. Demand All market sectors experienced greater requirements for coal in 1984. Electric utility coal consumption increased 6.3%; exports climbed 4.8%; coke plants consumed 18.9% more coal; coal requirements in the other industrial sector expanded by 11.8%; and consumption in the residential/commercial sector rose 8.1%. Domestic consumption of coal reached a record 718 Mt (791 million st) in 1984. This is a 7.4% gain over the previous consumption high of 668 Mt (737 million st) in 1983. Electric Utilities The 4.6% increase in electric power generation in 1984 was coupled with expanding coal use relative to other energy sources. This resulted in a 6.3% rise in coal consumption, totaling 603 Mt (664 million st) for the year. Thirty-eight of 45 states where coal-fired electric power plants were operating shared in the 36-Mt (39 million-st) increase in electric utility coal consumption

Jan 5, 1985

By K. A. Natarajan, M. K. Yelloji Rao

The electrochemistry of sphalerite and chalcopyrite was investigated under both open-circuit and applied potential conditions. Emphasis was placed on the selective dissolution of sphalerite from a mixture of sphalerite-chalcopyrite flotation concentrates as a function of applied potential, acid concentration, pulp density, and time. Morphological studies using a scanning electron microscope (SEM) were also carried out with chemically leached, galvanically leached, and unleached surfaces of sphalerite and chalcopyrite. Selective dissoulution of sphalerite could be achieved if the mixed chalcopyrite-sphalerite concentrate slurry was maintained at a negative applied potential of -0.4V (SCE). Probable mechanisms involved in the selective dissolution of zinc are disscussed.

Jan 1, 1990

By James F. Archibald, Ferri Hassani, Jacques Nantel, David O. DeGagné

Operators depend upon the success of backfilling programs to ensure that mine activities run continuously (Archibald et al, 1993) where backfilling is an integral part of the mining cycle. In order to ensure that the backfill is prepared and delivered to the stope possessing the required engineering properties, as designed, and that the backfilling process is safe, mine operators at all stages of the backfilling system must be adequately trained for their tasks and be aware of how their work affects other backfilling stages, both up- and down-stream of their station. Mine operator training is primarily based on learning on-the-job from experienced supervisors or training personnel. Classroom training and the availability of reference manuals are less common. While in use by many industries for some time now, computer-based training (CBT) is becoming more readily accepted by the mining industry for a wide variety of training. It is not intended to replace on-the-job training, but to augment it. CBT offers many advantages to enhance operator learning by utilizing multimedia presentations, interactions and on-line testing to teach complex concepts and relationships. Discussions with many operations revealed that there is an industry need for a backfill guide for frontline operator training and as a reference manual for operators and mine engineers. Sponsored by the mining industry and the CIM, "Mine Backfill, An Operator's Guide" has been developed by the Departments of Mining Engineering at Queen's University and McGill University to fulfil this need. "Mine Backfill, An Operator's Guide" is an interactive multimedia package that incorporates high quality colour images, animations, sound, and video with text to review the main backfill methods employed in Canada, including hydraulic/slurry, paste and rock fill. The Guide is divided into training and reference primer sections. When in training mode, the operator is guided through a presentation of common mining and backfill practices and technologies so that he/she may become more familiar with different aspects of backfill processes. To ensure that key concepts have been learned during training, the operator will be tested after each section using a series of multiple choice and true/false questions. When in reference mode, alternatively, the operator may browse through the information in a more detailed and independent fashion through a series of interactive menus. The Guide focuses on the following main topics: resources, surface preparation, distribution, stope activities, health and safety, and quality control. Special features included in the Operator's Guide are a Buyer's Guide, a Trouble Shooting Guide, and an interactive glossary of backfill and mining terms. Concepts in interactive and computer-based learning are also reviewed in this paper.

Jan 1, 2001

By Richard R. Klimpel, Basil F. Fee

This paper summarizes the status of a series of new chemical reagents developed with the explicit goal of expanding the capabilities of existing froth flotation processes as well as allowing for new solid/solid separations to be undertaken that are not now feasible with flotation. The first portion of the paper briefly outlines the theory and motivation behind the development of each new reagent family. 'The second portion of the paper deals with specific laboratory examples of some separation systems studied to date.

Jan 1, 1993

By R. B. Krog

Airflow patterns in longwall bleeder systems are affected by gob permeability and porosity and the condition of the gateroad entries after mining. As longwall panels are mined, areas of the caved zone and portions of the remaining gateroad entries become inaccessible, making direct ventilation measurement impossible. Mine operators are left to estimate direction and amount of airflow in the gob and the surrounding gateroads. The most readily available locations are where air enters the worked-out area, approved measurement point locations (MPLs) and/or evaluation points such as bleeder evaluation points, intake evaluation points, and the outer bleeder entry. Ventilation models (network or Computational Fluid Dynamics, CFD) can model the gob and the surrounding bleeder system but calibrating these models is difficult without field data. NIOSH installed a tube sampling system ahead of a longwall face and, as the face retreated, released a slug of tracer gas (SF6) to determine transportation times and flow rates in the inaccessible gateroads. The data was used to calibrate both network and CFD ventilation models for a longwall panel. Both model types were used to predict the airflow patterns in the gob and to determine the airflow rate from the longwall tailgate corner back to the bleeders.

Jan 1, 2011

By M. A. Chandler, G. T. Adel, J. N. Richardson, E. C. Gutierrez

A rapid, bench-top analyzer has been developed to determine P2O5 content and CaO/P2O5 ratio in phosphate ores. The analyzer utilizes a portable computer equipped with a frame grabber to measure the reflective intensity (gray level) of phosphate samples placed in front of a television camera. P2O5 content is related to the average gray level of the sample, while CaO/P2O5 ratio is determined from the amount of bright material present. The sensor is currently being used to analyze flotation concentrate samples at Texasgulf's phosphate operation near Aurora, North Carolina. Sensor development along with results from laboratory and in-plant testing are discussed.

Jan 1, 1993

By Paul C. Miclea

With the growing urban population and the concern for traffic congestion and pollution (emissions control), public transportation is becoming more and more attractive to both city dwellers and managers. To gain access to the central area of the city, the sub- way remains the most viable alternative, despite its higher cost when compared to above ground or elevated transportation systems. There are relatively few regulations and criteria for subway ventilation, particularly when compared with mine ventilation. The main document that provides guidance and general recommendations for subway ventilation and environmental control is the Sub- way Environmental Design Handbook, published in 1976 (2nd edition) by the U.S. Department of Transportation, Office of Re- search and Development. Many of the subway systems in existence today have been designed and built with ventilation features adequate for normal train operation, but their design does not consider stringent criteria for such emergency conditions as a train fire in a tunnel. The National Fire Protection Association's Standard for Fixed Guideway Transit Systems known as NFPA 130 as well as the ASHRAE Handbook - HVAC Applications (1995) provide specific design and operation requirements for subway ventilation systems. Some of the existing, old subways are upgrading their ventilation systems to comply with the new regulations. The ability of a particular ventilation system design to provide adequate ventilation during normal and emergency conditions can be evaluated using computer modeling and simulation techniques. A train fire will cause a sudden change in the tunnel ventilation pattern by adding an unsteady and fast-growing source of heat. The hot air and gasses created by a fire will tend to flow uphill, possibly against the normal flow, producing a 'backlayering effect." To prevent this effect from happening, enough ventilation must be provided and the governing criterion to establish the required airflow is called 'Critical Velocity." Several software packages are available for special applications on tunnel and station ventilation as well as to model the spread of smoke and heat in case of a major tunnel fire, using Computational Fluid Dynamics. This paper presents the current issues in subway ventilation, as shared by the public transit community around the world, together with modern alternative design concepts vis-à-vis the more stringent emerging Fire-Life Safety criteria. Examples of recent studies and ventilation systems design are provided.

Jan 1, 1997

By George W. Luxbacher

The inclusion of a new term "planned subsidence" in the Surface Mining and Reclamation Act of 1977 has lead the U.S. coal mining industry into a new aspect of engineering: subsidence planning. Subsidence planning has necessitated the integration of geotechnical, civil, and mining engineering disciplines. Although much of the foundation and application work has been completed, subsidence planning is still a developing area. This paper discusses the application of subsidence planning in several brief case studies (a high voltage transmission tower, a sewage treatment plant, and a slurry impoundment), emphasizing the risk assessment aspects necessary to account for some of the uncertainties that may exist.

Jan 1, 1986

By A. W. Scaroni, C. Y. Tsai

The effect of particle size and composition on the pyrolysis and combustion of a pulverized bituminous coal in an entrained-flow reactor has been investigated. Predicted time-temperature histories of the coal particles and experimental weight loss data indicate a strong coupling of heat and mass transfer to the pyrolysis and combustion rates. A higher combustion rate following ignition was observed as particle size was increased to 112 µm (about 140 mesh). This is related to a higher particle temperature after ignition for the larger particles. Although the heating rate before ignition decreases with increasing particle size, higher slip velocities and surrounding gas temperatures for the larger particles promote early ignition. The presence of liptinite in the coal increases the weight loss rate before and immediately after ignition. Similar behavior was observed for pyrolysis. Fractions of an HVA bituminous coal that were rich in mineral matter or semi-fusinite were found to have a higher heterogeneous char combustion rate than vitrinite-rich samples.

Jan 1, 1987

By H. E. M. N. Moursy, Hassan El-Shall, M. N. Ahmad, Ponisseril Somasundaran, C. R. Holland, D. Chandler, G. Walker, Regis Stana, Patrick Zhang

The reaction kinetics of the acidulation of Moroccan phosphate rock (32% P?05) using 45% nitric acid were investigated using the Shrinking Core Model (SCM) , a newly developed Diffusion Model (DM) and a newly developed Combined Reaction and Diffusion Model (CRDM). This was achieved buy conducting a number of experiments in a controlled batch reactor system at different temperatures. The conversion and the reaction rate were calculated at different time intervals. The SCM based on reaction time and the CRDM characterize the acidulation process of phosphate rock. Diffusion of nitric acid and the products of acidulation at the early stages of reaction through the phosphate rock were found to be the rate-controlling step, resulting in a dif- fusion coefficient, which controls the mass transfer process. The reaction kinetics were found to fit first-order kinetics especially during early stages of reaction time. The deviation of the kinetics from first-order at later stages was due to the fact that the overall reaction was mass transfer controlled with respect to nitric acid and products diffusion.

Jan 1, 2002

By Joel Nonnweiler, David Young, John Hawley

The Sacramento Regional County Sanitation District has implemented a billion-dollar interceptor system master plan, including the 31 km (19 mile) long Lower Northwest Interceptor (LNWI). For the two LNWI Sacramento River crossings, pipe-jack/micro tunnel drives in excess of 300 meters (1,000 ft) from 30 meter (100 ft) deep shafts in mixed soil conditions below the water table were considered, as were600 meter (2,000 ft) tunnel drives utilizing pressurized-face tunnel boring machines. Operation and maintenance concerns, predicted flood scour, and levee concerns are discussed. A risk assessment process was used to select both profile and construction method. Construction will begin in mid 2004.

Jan 1, 2003

By Richard Hogg, Erol Kaya, Jan M. Mutmansky

Characterization of the size, shape, chemical composition, and mineralogical content of mine airborne dusts generally requires a larger mass of dust particles than is typically collected using traditional sampling devices. In this paper, the general design of a passive dust collector is described and the field results are presented. The collector was constructed of galvanized sheet metal duct with a resin-coated honeycomb to provide an elutriation-type system for particle collection. Several versions of the collector were used in the field portions of the research. The dust samples collected from underground coal mines were found to possess angular particle shapes, relatively consistent size distributions, and elemental compositions that showed relatively little variation, at least for the more prevalent elements. In addition, the distributions of particles sizes obtained from the passive dust collector appear to be similar to those of samples collected at the same time in a conventional personal sampler except that the passive device seems to collect a larger quantity of coarse, non- respirable particles. Conclusions on the suitability of this dust collector for collecting characterization samples are presented. In addition, the potential for using such a dust collection system for supplying dusts for biomedical research is discussed.

Jan 1, 1993

By Frank A. Aplan, Barbara J. Arnold

INTRODUCTION Coal flotation is a fine cleaning process usually present in all but the older preparation plants. It is typically used to clean either the -28 mesh (-500 pm) or - 100 mesh (- 150 pm) raw coal fines, and it is the only commonly used preparation method that can effectively recover coal particles finer than, say, -200 mesh (74 pm). To place coal flotation into its proper context, it should be noted that the bulk of the raw coal sent to preparation plants is treated by gravity concentration. On a worldwide basis, from 0 to 40% of the raw feed to a preparation plant is treated by flotation, while in the US only about 10% of the raw coal feed is floated. Roughly, 50% of US preparation plants use flotation to process at least a portion of the raw coal feed, although most of the newer plants incorporate flotation into their flowsheet. Historically, the process has only been used to treat the raw coal fines naturally occurring after mining and a minimal amount of crushing at the preparation plant. This is in sharp contrast to ore flotation where, typically, the entire tonnage is first ground and then floated. As a consequence, of the approximately 500 Mt of raw coal treated by preparation in the US yearly, it is estimated that only about 40 Mt are sent to the flotation circuits (producing -30 Mt of clean product).'O1 This small tonnage compares with about 400 Mt of ores treated annually in the US by flotation. By analogy to ore flotation, where it is an effective, large tonnage, low cost, easy to operate process, its potential in coal preparation should be great. Reasons why it has not achieved a greater potential in coal preparation have been attributed by Aplan 102 to: 1. Indifferent results in removing sulfur and ash. 2. Difficulty in floating low rank and oxidized coals. 3. Inability to make clean separations with the finer sizes. 4.Inability to clean slurries with a high percentage of clay. 5. Problems with water chemistry. 6. Competition with effective, gravity coarse-cleaning methods. 7. Low value of coal historically. 8. Dewatering problems. 9. Transportation and storage problems with coal fines. 10. Marketing problems with coal fines. 11. Inadequate attention to the process in the plant. 12. Inefficient use of capital and operating monies. Inadequate attention to procedures, machines, and processes.

Jan 1, 1991

By G. D. Schena

A decision support system for the management of the mineral resources of a developing country has been derived. The system allows the evaluation of the impact of a mineral project in a developing country in the broad context of its economy. The analysis permits the assessment of the overall socio-economic consequences of mineral prospects and allows incorporation in the evaluation of issues that are broader in scope than the pure financial objectives. The system is built around the Leontief framework of economic analysis. The original input-output model, enhanced to incorporate country-specific behaviour is integrated with cost-benefit analysis and shadow pricing. The analysis leads to synthetic measures of profitability at market and shadow prices. These measures are useful to direct the mineral policy of a developing country through the exploitation of those mineral resources which are most likely to bring about economic growth and social advancement.

Jan 1, 1992

By Thomas A. Wheeler, Robert O. Keys

The choice of the flotation reagent that suits a particular coal has become more complicated with the development of new, more efficient reagents. Frothers and conditioning reagents, in particular, have experienced a dramatic reevaluation of their role in floating various types of coals. This paper offers a better understanding of how each of the following factors contributes to the reagent selection: 1. Natural Flotability 2. Degree of Oxidation 3. Size Distribution 4. Percent Solids in Feed Slurry 5. Fluctuations in Plant Feed 6. Limitations on Froth Handling 7. Clean Coal Specifications 8. Ash Content in Feed a) discrete ashable minerals b) inherent ashable minerals 9. Water Chemistry 10. Petrographic Composition of Coal 11. Free-Swelling Index 12. Convictions of Customer The application of conditioning reagents - both promoters and emulsifiers can substantially improve the coal recovery. Some low-rank, hydrophylic coal, previously considered unfloatable can be economically recovered with the use of the proper reagent.

Jan 1, 1986

By R. Hogg, L. G. Austin, R. C. Klimpel

Slurry densities and holdup were measured for open circuit grinding tests in a laboratory overflow ball mill of 0.3 m diam by 0.6 m long, by emptying and drying after stoppage of the mill. Contrary to some other results in the literature, there was negligible variation of slurry level in the mill as a function of flow rate over a range of increase of flow rate of about 5 to I. However there was a gradual increase of solid holdup at higher flow rates because the slurry density in the mill increased. Equations are given for holdup and slurry density in the mill as a function of over flow diam, ball load, and feed slurry density. The average level of slurry necessary to give over flow was found to be much higher than that necessary to fill the mill to the overflow level at rest. The total level of balls and slurry was only increased slightly by ball loads higher than the overflow level. The overflow diam appeared to be the major controlling factor in determining the mill holdup.

Jan 1, 1990

By Jon P. Stone

The Automated Minerals Information System (AMIS) is an integrated data base system being developed to support the Bureau of Mines minerals information collection and analysis activities. The system facilitates cross-referencing and integration of domestic and foreign information from a variety of sources. The AMIS provides a central source of minerals information that is versatile and responsive to the needs of problem and policy analysts as well as supporting the needs of those involved in data collection and interpretation. As the AMIS becomes fully implemented, it will become an important tool in forecasting and assessing the impact of policy decisions that affect the supply and demand for minerals. The Bureau of Mines has long been the Federal Government's principal source of worldwide information on non-fuel minerals. Emphasis is placed on the analysis of mineral problems and policies as they affect the world's nonfuel mineral resources. To facilitate timely and accurate analysis, comprehensive data on 87 commodities are collected by various Bureau programs. Minerals information is made available through a number of periodic publications including the annual Minerals Yearbook and monthly Mineral Industry Surveys. These data collection and analysis activities have traditionally been supported by over 200 separate information processing systems. The Bureau of Mines has begun to implement a broad information strategy to provide a better response to the mineral problems and issues of the 1980's. The cornerstone of the Bureau of Mines information strategy is the development of the Automated Minerals Information System. When fully operational, we believe that the AMIS will provide the Bureau of Mines with the most comprehensive source of minerals information available anywhere in the world.

Jan 1, 1982