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By Lance A. Roberts

The Federal Highway Administration (FHWA) has mandated the use of the AASHTO Load and Resistance Factor Design (LRFD) specifications for all new federally-funded transportation infrastructure projects beginning in October 2007. This includes the design of all geotechnical-related elements, such as deep foundations, which have historically been excluded from the LRFD requirements. The basis of the LRFD specifications is the application of a probabilistically computed parameter called a resistance factor to the foundation capacity in lieu of the traditional, and often arbitrary, factor of safety. Therefore, the process of computing resistance factors for use in the design of deep foundations is extremely critical to ensure a safe, efficient, and consistent design methodology. In this paper, various methods to calibrate resistance factors for use in the design of deep foundations are examined. The methods that are currently utilized to calibrate the resistance factors reported in the AASHTO LRFD specifications may be classified as the allowable stress design (ASD) method and the reliability theory calibration method using static capacity prediction techniques. These methods are compared to a ?t-z? model design methodology. The current methods focus exclusively on the strength limit state design of deep foundations. The advantage of the ?t-z? model methodology is that it can be utilized for both strength and service limit state design. In addition, the results show that resistance factors vary based on geological setting, construction method, failure criteria and deep foundation type. This variability in the resistance factors should therefore be integrated in the design to ensure that the objectives of the LRFD approach are satisfied.

Jan 1, 2008

The intent of this address is to look forward into the 21st Century and present certain thoughts as to how underground coal mining might be conducted. The views in this talk are based principally on the author's experience with mining practices in the United States. It may be difficult to accept, but the 21st Century is a mere 12 years away. What new techniques will be available? To develop an understanding of the way in which technology has been and could be changing, a two- stage analysis is made of mining technology for U.S. Coal. The first phase covers the period 1975 to the present, while the second includes 1960 to 1975. This historical perspective includes a view of underground production by mining methods, considerations of labour productivity, and a review of accident and fatality rates. Several topics are important features of this historical analysis. Among the most significant are: (1) the introduction of Ion-wall mining technology into U.S. underground coal mines, (2) the use of computers to assist in mine planning and design activities, (3) major efforts to improve health and safety performance, with emphasis on underground dust control, and (4) improvements in mining equipment with an eye towards increased reliability and up-time performance. Based on that historical perspective, projections are made in three increments. The first being immediately at the turn of the century, the second being a dozen or so years beyond that, and the third being at the quarter point of the 21st Century.

Jan 1, 1988

By J. Alton Burks, Roy C. Bartholomae

The chain conveyor is utilized extensively in underground mining to convey raw ore, especially coal. It is estimated that several thousand loading and continuous mining machines rely on this type of conveyance. Although the chain conveyor is both efficient and highly reliable, its use is generally associated with the production of noise levels that often exceed 105 dBA at the operator's position. Thus, it is one of the most significant contributors to the occupational noise problem experienced by miners in the underground coal mining environment. Conventional engineering noise controls that result in an average reduction of 4 dBA have been previously designed and implemented. However, a novel solution involving a change in conveyor operation has been proposed that takes advantage of two aspects of conveyor noise: 1) conveyor noise has an approximately cubic dependence on conveyor chain speed and 2) due to the damping provided by coal, a full conveyor is 5 dBA quieter than an empty one. An engineering analysis has shown that a significant reduction in the operating noise level of a typical continuous miner can be achieved through the use of an adjustable speed drive automatically controlled by a coal loading sensor that maintains a full conveyor at all times. The potential reduction depends primarily on the mining conditions (coal seam thickness and the presence of either rock or water) and varies from 7-18 dBA. Other benefits to be derived from the use of a variable speed drive include reductions in power consumption, dust, and maintenance costs.

Jan 1, 1992

By A Califice, E Pirard, M Benzaazoua, R Mermillod-Blondin

Image analysis is more and more considered as a powerful tool for quantitative analysis of ores and concentrates. Apart from being very much dependent upon the quality of the imaging principle and the adequacy of the imaging sensor, quantitative image analysis is also the result of a long chain of material, image and pixel sampling strategies. The most reliable way to demonstrate the accuracy and the precision of modal analysis obtained from images is probably to use a blended material with known proportions of pure minerals and confront the results obtained from different analytical tools. This operation has been performed on a series of mineral blends mimicking the tailings of a flotation operation in a plant operating on massive sulfide mineralisation. The intention was to be able to better predict acid mine drainage potential from direct mineralogical observations. Selected sulfide minerals: pyrite (Py), pyrrhotite (Po), chalcopyrite (Cp) and sphalerite (Sp) were mixed as variable amounts within gangue minerals (quartz, calcite, dolomite and siderite). Typical blends contained six to ten per cent (Py); one to three per cent (Po); 0.5 to one per cent (Cp, Sp); 15 to 40 per cent carbonates and 40 to 75 per cent quartz by mass. The 1000 gram blends were carefully sampled and prepared for X-ray diffraction, chemical analysis by ICP-AES and optical microscopy image analysis (OMIA). Results obtained for the different analytical techniques are compared and discussed revealing the limits and strength of each method in the accurate quantification of sulfide and gangue minerals.

Jan 1, 2008

In the UK as existing face capacity is replaced, many of the new faces will have higher installed powers and be located in zones of higher strata temperature. These factors coupled with the need to increase production will result in more faces experiencing environmental difficulies, especially with respect to climatic conditions. In many cases these problems are unlikely to be solved, as in the past, by simply increasing the face air quantity. Therefore other techniques including refrigeration will be necessary, possibly requiring major capital and operational expenditure. It is easy to spend large capital sums and incur high operational expenditure without achieving the desired amount of climatic control. There is therefore a great need for reliable prediction techniques to aid in the making of sound, informed decisions which will have a significant influence in the long term on the level of production costs. A computer program able to predict the heat flows and resultant climatic conditions on a long¬wall coalfaces has been developed. Throughout it's development underground measurements have been used to validate the computer model and it has been shown that for an advancing coalface under normal production conditions that the program predicts the climate to within 1°C of the measured conditions. This paper outlines a number of methods available to improve climatic conditions on longwall faces. The coalface temperature prediction program is used to quantify the effects of these methods on the climatic conditions for a model coalface and a comparison is given. In conclusion a cool¬ing strategy for longwall faces is outlined.

Jan 1, 1991

By Clemens Jones

An interesting paper by J. E. Merion and Edward Hart, in Volume I., No. 2, of the Journal of Analytical Chemistry, on the Decomposition of Blast-Furnace Cinder by Acid, describes a plan of sampling the cinder by means of a previously-heated iron bar thrust into the cinder car or into the cinder at the notch, and then allowed to cool, thus chilling the cinder which adheres to the bar, and rendering it decomposable by hydrochloric acid, of 1.12 sp. gr. A short series of results is given, from which the deduction follows that blast-furnace cinder " is decomposed perfectly when chilled." Where many silica determinations are to be made, this method, if reliable, would effect notable economy of time and reagents. The conversion of insoluble silicates by fusion with an alkaline carbonate, together with the subsequent solution, evaporation, drying, etc., is destined to remain the standard method. But all fusionmethods are time-consuming and expensive. Chilling appears to render the supplementary method available for all practical purposes, in the determination of silica in cinder. But, with a view of securing more evidence on the subject, and in view of the fact that uniform results were not obtained by employing this method, it was decided to test the method in the laboratory of the Thomas Iron Company where a large number of silica determinations are made. The experience met with may not be devoid of value, both theoretical and practical. Mr. Iles's paper, in the Chemical News, Volume L., 1881, doubtless suggested to several chemists, connected with iron metallurgical

Jan 1, 1888

By Robert A. Haney

During the last ten years, longwall mining systems have undergone many changes. Panel widths and lengths have increased. Longwall faces have become more automated. Average production from individual longwall panels has increased from 1,000 to 3,600 tons per shift. To control the dust generation resulting from the higher production, longwall dust control systems have integrated various dust control techniques. Systems designed to control dust generated at the crusher/stageloader, shearer, and supports are common to most longwall faces. A survey was made of the dust controls that are currently in place on all the longwalls in the U.S. This survey addressed the types of controls used to reduce dust generated at the crusher/stageloader, shearer and roof support movement. Additionally, information on face ventilation rates, cutting cycle and level of automation was obtained. The purpose of this paper is to review the dust control practices that have been implemented throughout the United States and to identify those controls that are being used on high production longwall faces. Additionally, a model is used to demonstrate how ventilation and automation affect occupational exposure. Automation of roof support movement can offer some of the greatest reductions in occupational dust exposures. While technically feasible, its full benefit has not been fully realized by the industry. Until technology to fully automate longwall mining systems becomes more reliable, future dust control systems must rely on increased ventilation, application of headgate dust collectors, improved shearer dust controls and improved shield dust suppression systems.

Jan 1, 1995

In the wake of the financial crisis that affected world markets in 2002, there has been an increasing international focus on corporate governance. Various corporate governance codes of practice have been introduced, such as the Sarbanes-Oxley legislation in the USA, the Combined Code in the UK, and King III in South Africa. This focus on corporate governance has increased since the most recent financial crisis in 2008, the effects of which are still being felt world-wide. In the mining and minerals industry, reliable metal accounting is essential to sound corporate governance and is also becoming a focus of increased attention and concern, particularly as the figures generated by the metal accounting system feed directly into the financial accounts of mining companies. Mass measurement, sampling, and analysis provide the input data for the metal accounting system and sound corporate governance requires that the procedures used are based on best practice and that the data generated is accurate and handled correctly, transparently, and consistently to produce the accounting reports. The AMIRA Code of Practice for Metal Accounting has been widely adopted in the industry as a means to achieve this, and the compilers of the Code have conducted numerous metal accounting audits at operations, both in South Africa and abroad. These audits have shown that there is a real need for such a code of practice. Keywords metal accounting, AMIRA Code, corporate governance, risk management.

Jan 1, 2014

By R. V. Ramani, W. Miola

The MSHA prescribed method for the determination of quartz in airborne respirable-dust samples from underground coal mines is the P-7 method, a combination of low-temperature, radio-frequency ashing (LTA) and infrared analysis (IR). There is no prescribed procedure for quartz analysis in bulk samples of coal and host rock. Dispersive infrared (IR), Fourier-transform infrared (FTIR) and X-ray diffraction (XRD) methods are most commonly used for the analysis of quartz in powders. Several aspects of the experimental procedures, such as the preparation of the analysis sample from bulk samples, ashing techniques, scanning procedures, peak measurement location, calibration techniques, sample amounts, size consist and data interpretation, affect the results from each of the methods differently. Significant differences in analytical results obtained from X-ray diffraction (XRD) and infrared spectroscopy (IR) on the same samples are reported. All studies point to the need for reliable quartz analysis methods. In a recent research program, a procedure for preparing bulk-coal and host-rock samples for quantitative quartz analysis was developed. Further, the results from X-ray diffractometry and infrared spectroscopy for quartz content on identical samples were compared. Calibrations with pure and mixed standards were used to assess the influence of particle-size distribution, matrix and calibration on the analytical results. In this paper, several issues concerning the measurement of quartz in the samples of coal, host-rock and airborne respirable dust from mines are outlined and quantified.

Jan 1, 1996

By Allan E. Hall, Stephen G. Hardcastle, Lucien D. Nel, Jean-Paul Saindon

A description is given of the investigation conducted at Sherritt Gordon's Ruttan Operation in Manitoba during 1986. Gas and dust concentrations were measured in the exhaust air of the major working sections to assess the potential for recirculating exhaust air into the intake air in winter to reduce heating costs. The results indicate that there is excellent potential to significantly reduce winter heating costs by controlled recirculation of exhaust air. Gas and dust concentrations vary significantly during the working shifts but have consistent trends from shift to shift and day to day. The variations in gas concentrations have similar trends but no single gas could be reliably used to predict the variation of the other gas or the dust concentrations. Dilution and the other effects which reduce pollutant levels as the exhaust air returns to surface indicate that recirculation should take place as close to surface as possible, subject to the economic constraints of the airway construction required and the extra fan energy required for the longer recirculation path. Recommendations are made for the choice and positioning of air and dust monitoring sensors and the logic of a control system. Economic analysis of the results indicates that controlled recirculation is viable at an existing mine with a pay back period of approximately two years. Incorporation of a system into a new mine at the planning stage would significantly shorten the pay back period.

Jan 1, 1987

By Paivi Suikkanen, Kari Hietala, Kaarlo Haavanlammi

"Processing of high-magnesia concentrates, the recoveries of nickel and copper, as well as those of platinum group metals (PGM’s) and cobalt are key issues of the Nickel Smelting technologies. PGMs are typically found in association with each other, but also importantly with nickel and copper. A challenge of producing saleable concentrates at acceptable recovery degrees, an increasing focus on the sustainable use of metals and recent decreases in the value of nickel has increased the interest to find a reliable route from Cu-Ni-PGM bulk concentrates to product. According to studies, most efficient process for Ni-Cu-PGM concentrates is flash smelting using DON process20 years ago, in 1995, Outokumpu commenced at Harjavalta a new Nickel Flash Smelting technology based on the Direct Outotec Nickel (DON) Smelting Process. The DON process enables production of high-grade nickel matte with low Fe-content directly in the Flash Smelting Furnace (FSF) without subsequent converting. Metal values from the smelting slag are recovered in the Electric Furnace (EF) as iron containing Ni-matte. Matte refining is based on atmospheric pre-leaching and total pressure leaching. Nickel, cobalt and iron are leached leaving a leach residue containing small amount of gangue minerals and PGM’s. Iron is removed from the leach solution in and nickel will be recovered with standard methods. Overall > 95% metal recovery can be expected with low energy consumption and low environmental impact."

Jan 1, 2014

By Isobel Clark

The problem of the estimation of ore reserves is essentially a simple one to describe. Given a set of sample data, at specified locations within a deposit, how can we estimate the value (or quantity) of ore in unsampled areas. The question may be posed of a whole deposit (global) or it may be more desirable to estimate smaller volumes within the planned mine area, e.g. stopes or blocks (local). Many methods have been evolved to tackle this problem, from hand-contouring of values by the mine geologist to extremely sophisticated geomathematical analysis. The main difficulty with any estimation method in this context is that it is almost impossible to check whether the "predicted" value bears a close relationship with the "actual" value. The only reliable way to decide if an estimation method has "worked" is to test the eventual value of ore against the predicted value. This is, more often than not, impossible - even allowing for the time factor involved. To know the "actual" value of a mined block it has to be sampled intensely, and these values with their positions recorded accurately. Alternatively, blocks may be passed through the concentration process individually and these results recorded. In most producing mines neither of these alternatives are practicable or seen to be-important. Another problem with comparing in-situ (so-called) mineable reserves with production figures is the introduction of many variables into the concentration process -- dilution, wastage, possible stockpiling, mill recoveries and so on.

Jan 1, 1979

Hamersley Iron Pty. Limited has maintained an interest in the screening of iron ore fines (nominally -6 mm). However, no dry screening process had successfully demonstrated acceptable separating efficiencies at high tonnage rates, low operating costs, and mechanical reliability when screening iron ore fines (containing up to 6% free moisture) at sizes of around 1 to 2 mm. A new type of vibrating inclined screen has recently been developed which is claimed to have a non-blinding screening surface. It was decided to test a pilot scale unit in an existing pilot plant located at Hamersley's facilities at Dampier, Western Australia. The appropriate operating parameters such as vibration speed and feed rate were determined using one fine ore type. Mats with different aperture sizes, and different feed moisture contents were also tested. Trials were then conducted on various fine ore types to indicate the effect of different size distributions on separating efficiencies. The effects of feed moisture content were determined with these ore types, and a blend of lump (nominally -30+6 mm) and fines was tested to compare the screen's performance with that of the bottom deck of the minesite product Screens.

Jan 1, 1991

By James V. Thompson

SINCE it was introduced in 1943 to recover chromite from Oregon beach sands, the Humphreys spiral concentrator has proved successful in several fields of wet mineral beneficiation. By the end of 1957, 9390 Humphreys spirals had been manufactured. Most of these are still in service. The spiral does not offer a panacea for all mineral dressing problems. Its proper application can best be determined by test work. Spirals present a unique advantage for the metallurgist to make tests in a full-size machine rather than a miniature model, without the risk involved in scaling up results. With only 10 to 40 lb of sample, the operator of a closed circuit test unit employing a full-size Humphreys spiral can conduct preliminary tests with full-scale loadings of 0.5 to 2.5 tph. With larger samples, from 300 to 500 lb, he can run longer multi-stage tests to obtain reliable data for the next step-pilot plant design. The manufacturer of the Humphreys spiral concentrator maintains a fully equipped ore dressing laboratory and by insisting on test work prior to sales has largely prevented misapplication of the spiral.

Jan 1, 1958

Reliably detect fires by sensing sub-micrometer-sized particles released into the air by smoldering or burning materials. Approach An extremely sensitive, ionization-type fire detector has been built that continuously draws air samples through its ionizing field and collects the ionized smoke particles downstream, thereby generating a proportional electrical output signal. (An offshoot instrument measures the size distribution and number of sub-micrometer particles in air.) How It Works Mine air to be monitored is drawn through the instrument assembly by a small pump. A pre-filter and cyclone remove dust particles and other particles larger than 0.6 micrometer diameter. The air and remaining aerosol-sized particles flow through a gastight tube which contains the detector. See diagram. Smoke and other sub-micrometer-size particles moving Into the detector, pass through an Ionizing field, and are struck by alpha particles released from radioactive source located on the axis of the tube, The alpha particles move radially outward until they strike smoke particles or molecules of air or water. When struck, a smoke particle or molecule loses an electron and becomes positively ionized.

Jan 1, 1979

By H. F. Haller

COLUMBIA-SOUTHERN'S Barberton limestone mine, 8 miles southwest of Akron, Ohio, is a million-ton-per-year producer from a depth of over 2200 ft in a district where other underground mining at this depth is unknown. Mining extracts 46 of the top 51 ft from a formation of Devonian limestone discovered by drilling in the 1890's. The same drilling revealed extensive salt deposits below the lime- stone, which led to the location of the chemical plant at Barberton as a division of the Pittsburgh Plate Glass Co. in 1899. Soda ash was the principal product of the plant, and as production increased the demand for limestone increased. Columbia's first attempt to secure a reliable all-weather source of stone was the development of a quarry at Zanesville, Ohio, in 1919. Zanesville production eliminated some of the stock- piling required by the use of Michigan stone, avail- able only during the lake shipping season. Stone from some Zanesville horizons, however, was found to be more suitable for cement production than for soda ash, and rail transportation remained an important factor. As demand continued to increase, plans were made to develop the Barberton deposit.

Jan 12, 1954

By Roberto Zaragoza

Historically, the control of flotation operations has been viewed by many as an art. Only recently has process measurement and control come to be viewed not as an ?art? but as a very complex and productive science. In recent years, process control applications to flotation plants have been established and already some gains have been reported for several industrial operations using individual stabilizing control loops including level, pulp flow, pulp density, reagent addition rate and pH (Paakinen, 1979; Hales, 1985). The use of process control computers combined with on-line x-ray florescence (XRF) in industrial flotation circuits has made the application of more sophisticated control techniques feasible in the mineral recovery process. In spite of the availability of reliable instrumentation in modern flotation plants, satisfactory control strategies are difficult to develop and implement. Extremely important factors such as changes in ore type, liberation characteristics, flotability, degree of oxidation on particle surfaces, and specific gravity constitute unmeasured disturbances to the process. Most current control systems cannot adapt specifically to such disturbances.

Jan 1, 1987

By M. K. Barnett

Engineering research consists, broadly speaking, in the investigation of the effect of the variations in a number of factors on some property of a product or characteristic of a process. The unambiguous description of the product or process requires that the property or characteristic be expressible in quantitative terms. For the purpose of practical control, it is likewise desirable that the independently variable factors governing the product or process be quantities, although this ideal goal is not always attained. Maximum efficiency—i.e., the attain- ment of the maximum amount of reliable, useful information relating to the influence of, the factors on the property of the product or characteristic of the process, for the least expense—is an important requirement for the satisfactory operation of a research organization. Obviously, a necessary condition for the attainment of maximum efficiency is an adequate knowledge of the specialized field in which the experimental research lies. While necessary, this condition is not sufficient. Proper attention must also be given to the general principles of experimental design together with the modern methods for the analysis and evaluation of experimental data. The Present discussion is confined to a single design, the so-called "factorial" design. This design is of special interest in that it attains its goal, maximum efficiency, by directly departing from the

Jan 1, 1948

The concept of optical basicity is now being widely applied to rationalize and predict the chemical properties of slags. It employs signals from a probe ion to indicate the "state" or relative "freeness" of the oxygen ions in the slag, and hence provides a fundamental measure of slag basicity. Values of the bulk optical basicity of a slag can either be measured spectroscopically in samples of transparent solid glassy slag, or calculated very simply and accurately from the chemical composition of the slag. The way in which these values vary in different systems are illustrated as isoptical basicity lines on ternary diagrams, and the patterns obtained are discussed. The difficulties associated with assigning optical basicities to the oxides of transition elements are also reviewed briefly. It has been demonstrated that these bulk values can be used as the basis of a flux control model for steelmaking to achieve end-point chemistries much more reliably. Furthermore, several correlations have been established which allow the prediction of the slag-metal distribution of various solute elements. This approach has been used to predict the phosphorus distribution at the end of steelmaking, and also to custom design fluxes for the ladle and tundish to aid in the control of residual elements in the steel such as suphur, hydrogen and nitrogen.

Jan 1, 1990

By M. K. Barnett

Engineering research consists, broadly speaking, in the investigation of the effect of the variations in a number of factors on some property of a product or characteristic of a process. The unambiguous description of the product or process requires that the property or characteristic be expressible in quantitative terms. For the purpose of practical control, it is likewise desirable that the independently variable factors governing the product or process be quantities, although this ideal goal is not always attained. Maximum efficiency—i.e., the attain- ment of the maximum amount of reliable, useful information relating to the influence of, the factors on the property of the product or characteristic of the process, for the least expense—is an important requirement for the satisfactory operation of a research organization. Obviously, a necessary condition for the attainment of maximum efficiency is an adequate knowledge of the specialized field in which the experimental research lies. While necessary, this condition is not sufficient. Proper attention must also be given to the general principles of experimental design together with the modern methods for the analysis and evaluation of experimental data. The Present discussion is confined to a single design, the so-called "factorial" design. This design is of special interest in that it attains its goal, maximum efficiency, by directly departing from the

Jan 1, 1948