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By G. J. Joy, J. P. Rider

"Technical advances in longwall mining over the last several years have resulted in much larger and faster shearers that have the capability of mining at speeds over 100 ft./min. This has resulted in a substantial increase in the amount of dust that is generated at the shearer and during shield advances. Meanwhile, increased underground coal production has put a greater demand on longwall dust control systems as some operators have had difficulty maintaining consistent compliance with federal dust standards. To address this need, the National Institute for Occupational Safety and Health [NIOSH] is investigating the effectiveness of a water spray manifold mounted on the tailgate end of the shearer body. The sprays are oriented parallel to the tailgate ranging arm, and these sprays create a water curtain confining the dust plume near the face, preventing the dust from drifting into the walkway. This redirection of dust provides a clean air envelope for the tailgate shearer operator and jacksetters working near the tailgate drum. Three different tailgate spray manifold designs were tested and evaluated at the Office of Mine Safety and Health Research [OMSHR] Pittsburgh Longwall Test Facility. Manifolds were equipped with hollow cone or flat fan water spray nozzles and evaluated at three face air velocities (500, 700, and 900 fpm) and at water pressures of 100, 150, and 200 psi. Reductions in dust concentrations were observed at six face sampling locations for all the tailgate manifold systems at each of the tested spray pressures and face velocities. Based on results from the laboratory tests showing reductions in dust concentrations at sampling locations downwind of the shearer a spray manifold was fabricated and evaluated at an underground operation. INTRODUCTION In 2012, underground coal mining in the United States produced a total of 342 million short tons, with longwall mining accounting for over 53% of this production [EIA 2013]. The longwall mining industry continues to see remarkable and significant improvements in longwall mining equipment and mining practices. Average shift production during compliance dust sampling has increased from 3,500 tons per shift in 1994 to approximately 6,000 tons per shift in 2012. A dramatic decrease in working longwall faces from 80 to 49 has occurred over the same period [Fiscor 2013]. Factors specific to longwall mines that supported productivity improvement include: higher capacity shearers, improved shield hydraulics and control, higher horsepower for equipment, wider face conveyors, and larger faces. Today, the average face width has increased to 1,188 ft., with one longwall operation reporting a face width of 1,650 ft. compared to an average of 750 ft. in 1994 [Fiscor 2009, 2014]. Panel lengths in 2013 averaged 11,307 ft. compared to 7,000 ft. in 1994. Overall production from U.S. longwalls has increased by nearly four percent from 2007 to 2012 with over 182 million tons mined annually [EIA 2013]. Given the volume and rate of coal produced on longwall faces, the potential to generate large quantities of respirable coal mine dust also exists."

Jan 1, 2015

By JESSICA W. A. AZURE, Kansake A. Bruno, Samuel Frimpong, AZUPURI G. A. KABA, FORSYTH A. KADINGDI, PROSPER E. A. AYAWAH

Blasting generates undesirable ground vibration with adverse effects on humans, the environment, and structures. Numerous studies have used various techniques including machine learning (ML) to predict the peak particle velocity (PPV) caused by blasting in surface mines. These studies used the validation-set approach to evaluate the performance of their predictive models. In this study, Random Forest (RF), Gaussian Process (GP), and Gradient Boosting Machine (GBM) were applied for the prediction of PPV using data from a large open-pit gold mine in Ghana. An ensemble model based on a stacked generalization approach was then built on these three base models to significantly improve the PPV prediction performance. The model evaluation was done using repeated tenfold cross-validation which resolves the challenges with the validationset approach for small datasets. The dataset used in this study comprised a total of 196 measurements taken from different blasting operations. R-squared ( R2 ), mean absolute error (MAE), and root mean square error (RMSE) were used to evaluate the model performance. The results obtained from these models revealed that all the base models did not significantly outperform each other. However, the stacked generalization approach had a better performance, with RMSE = 0.12, R2 = 0.96, and MAE = 0.07. This approach presented an improvement over the existing methods and will be useful for highly accurate predictions of ground vibration during blast design. The application of this model will be useful for efficient and effective blast design.

Nov 8, 2022

By S. P. Chong, Peter V. Avotins

The iron and steel industry continues to operate at depressed production levels due to the low level of demand for steel and foundry products. Crude steel production in the Western world dropped by 13.7% from 459.3 Gt (506 billion st) in 1981 to 396.4 Gt (437 billion st). The reduction was particularly severe in North America where the industry suffered a loss of 37.3% from 123.6 to 77.5 Gt (136 to 85 billion st). This reduced level of production severely affected iron ore and agglomerates output. Substantial curtailment was made in both sintering and pelletizing plants to meet reduced demand. The pressure on these plant operators shifted from quantity to quality. With energy cost becoming an ever increasing part of production costs, conservation was a major area of emphasis. Iron Making Sinter has continued to be the favored burden for blast furnaces overseas. As hot metal production declined and excess sintering capacity developed, many of the overseas operators that have been using pellets found it advantageous on hot metal production cost to increase the ratio of sinter at the expense of pellets. This was the case despite the depressed price level of pellets in the world market. In North America where pellets have been the predominant burden material-mainly because it is necessary to pelletize the fine grain iron ores available domestically-there was also increased interest in sinter usage. Bethlehem Steel Corporation's 13.6-m (44.5-ft) furnace at Sparrows Point experimented with a burden with more than 70% of sinter during the second half of the year and indicated some favorable results as compared to its previous 50% super flux sinter and 50% acid pellet burden. The blast furnace operators continued to press for improved burden quality. In addition to the emphasis on the importance of burden chemistry and quality, uniformity, much emphasis was placed on improving reducibilitiy and high temperature metallurgical qualities. These burden properties were recognized to hold further promise in reducing fuels rates. Sintering With reduced consumption caused by the cutback in hot metal production, many sinter plants sat idle while others operated at greatly reduced rates. The deemphasis on production in many plants allowed them to experiment with various means to reduce operating costs. The most notable action was the introduction of low cost South American pellet feed fines into the sinter ore mix. These feed fines, which are finer than 150 µm (100 mesh) ore, were previously thought to be too fine for sintering. However, when the full production rate is not required the use of up to 40% in the ore mix was reported to be successful with the aid of burnt lime and adequate premixing and granulation of the sinter mix before sintering. The emphasis on quality and tighter cost control also has resulted in a further breakthrough in sintering technology. It was recognized that good feed preparation-including selection of compatible ores, good blending, good pseudo-particle formation, additive size control increased bed depth, and closed control of the sintering bed heat pattern-could allow the production of high quality sinters with much lower heat input and FeO level. Bed depth of more than 600 mm (23.6 in.) was practiced in a number of operations. Total heat input of better than 1.3 GJ/t (290,300 kcal per st) has been achieved. Kawasaki Steel's Chiba Works has also achieved a 5.3% SiO2 in the sinter with good quality. The low heat input approach allowed production

Jan 5, 1983

By H. Jiang, Y. Luo

The study develops an automated, high-efficiency drilling control system to reduce respirable dust and increase energy efficiency in underground coal mines. It uses specific energy to evaluate efficiency and proposes a comprehensive drilling control algorithm based on laboratory tests. The algorithm optimizes drilling parameters to maintain high efficiency, reduce dust generation, and improve safety.

Feb 12, 2022

By Peter Johnson, David Barber, Lachlan Henderson

"The traditional approach to rail tunnel fire safety design is to follow NFPA 130, which assumes a major tunnel fire could occur and requires bi-directional emergency ventilation. There is no regard to the impact of ventilation on fire growth and smoke production. In Europe and other parts of the world, the need for tunnel ventilation systems to provide smoke management in the event of fire is being questioned. The European Commission’s Safety in Railway Tunnels TSI is based on a philosophy that improved running capability (preventing fires and other events stopping the train in the tunnel) and elevated fire performance of materials means the chances of a major fire in a tunnel is highly unlikely, with only small fires expected, and no tunnel ventilation required. This approach is reinforced by the International Tunneling Association which has recently published an Engineering Methodology for Performance Based Fire Safety Design on Underground Rail Systems, which includes a methodology that does not require assessment of tenability in tunnels, but requires a scenario based risk assessment to be undertaken to determine overall fire safety measures. Recent research by the University of Edinburgh has shown that forced airflow from a mechanical ventilation system may promote fire growth and increase smoke volumes much more than with natural ventilation. Whilst the concept of no mechanical ventilation (i.e. natural ventilation) is a new concept for some, for many rail tunnels it is worthy of serious further consideration. RAIL TUNNEL SMOKE MANAGEMENT AND STANDARDS Smoke management using mechanical bi-directional ventilation systems has been a central part of the fire safety design solution under NFPA 130 for rail tunnels since 1982. The current version of the standard, NFPA 130: 2014, states that mechanical ventilation should be fitted to rail tunnels of length greater than 305 meters and an engineering analysis should be undertaken for tunnels of length 61 to 305 meters to determine whether mechanical ventilation should be fitted. However, this approach is not necessarily reflected elsewhere in the world. In Europe in particular, mechanical ventilation systems for smoke control within rail tunnels have taken a much less central role within the standards framework."

Jan 1, 2016

By J. G. Groppo

A beneficiation process has been developed to provide selective separation of unburned carbon from high LOI fly ash. Previous reports of utilizing froth flotation to achieve selective separations required long residence times and high reagent costs. A proprietary reagent system has been developed to address both of these limitations. Based on the results obtained from laboratory and pilot-scale investigations, a flowsheet design has been developed to produce two distinct usable products from class F fly ash; low LOI ash and a high carbon product suitable for reburning or further upgrading. A process flowsheet and description are presented.

Jan 1, 1996

By David J. Hatem

Public-private partnerships (PPP) are gaining in popularity at the federal, state and local levels as the public sector seeks private capital to finance infrastructure and other projects that traditionally have been funded with public funds. In general, a PPP involves a development agreement between a public owner and a private sector concessionaire. Under the development agreement, the concessionaire is responsible for financing, designing, constructing and typically operating and maintaining the completed project for a concession period (often multi-decades in duration). The concessionaire typically enters into an agreement ? the design-build agreement ? with a design-builder to design and construct the project. The concessionaire may secure financing from banks, investors or from a combination of these and other sources (collectively the financier). While the PPP experience in the United States has been modest to date, an increasing number of projects involving tunneling or other significant subsurface work are already being delivered in the PPP mode. Public owners have significant options to address risk allocation for subsurface conditions on PPP projects. The same sound and fundamental principles of fairness in risk allocation that apply in other major subsurface projects should be applied and adopted in the PPP context

Mar 1, 2014

By Ramon S. Pizarro, W. Joseph Schlitt

Introduction Trying to synthesize innovations occurring in gold processing is not simple. At present, this technology is exploding, brought about by the high price of gold. This price has compelled the mining industry, as a matter of survival, to produce gold. The frantic search for gold deposits continues, from glacial areas to tropical jungles. The search has been fruitful. New exploration techniques have helped to locate deposits. Some are amenable to conventional processing techniques. Others are in unusual settings that challenge the ingenuity of extractive metallurgists. Ore deposits containing traces of invisible gold, refractory mineralization, and impurities and deleterious materials that previously defied treatment are now being profitably processed. Metallurgists have developed various processing methods and equipment for gold ore treatment that reflect differences in ore characteristics, grade, mineralogy, reserves, topography, climate, and location. These processes can be categorized as: • For nonrefractory or readily leachable gold ores - vat leaching, heap leaching, and agitation leaching. • For ores containing free gold - gravity concentration methods, followed by mercury amalgamation, and • For refractory gold ores - flotation, roasting, pressure oxidation, followed by cyanidation leaching. In actual practice, a combination of these processes may be required. This is because gold mineralization, although usually simple, may be associated with other mineral species or with clays that make the ore difficult to treat. Furthermore, after the gold has been solubilized to form a cyanide complex, one of two important processes must be applied to recover the gold. These ore zinc cementation (Merrill-Crow process) and Carbon adsorption, desorption, and electrowinning. New techniques for leaching and recovery are also advancing. These will become the bases for the next generation of gold processing plants. Nonrefractory Gold Ores Nonrefractory ores with readily leachable gold are among the .easiest to treat. Even so, non-refractory ores from epithermal deposits are likely to contain too much clay. When these ores are damp, they may clog the screens and cone crushers. Depending on the type of process, scrubbing the crushed ore is very effective in overcoming clay problems. After dewatering, the slimes enter the cyanidation process and the thickener overflow is stripped of gold values and recycled. Semiautogenous (SAG) mills are also gaining popularity due to lower capital costs and ability to treat wet, sticky ores. If properly sized, the secondary crushing and screening plants, together with a secondary ball mill, can be eliminated. When the ore is of such a low grade that it can not support fine grinding, vat or heap 'teaching may be applicable. These systems are being actively applied in the US and elsewhere. Rapid construction and low capital costs are important features of these plants. Vat leaching is ideally suited for fast leaching ores and small tonnage deposits located in areas with harsh winters or wet tropical climates. For effective vat leaching, the ore is crushed to less than 25 mm (1 in.), agglomerated with lime or cement to control fines, and leached with sodium cyanide solution (upflow or downflow). The degree of size reduction is a tradeoff between increased costs of comminution and improved gold recovery from smaller particles. However, the size of material

Jan 11, 1984

By Carl C. Martin

The treatment of ores in preparation for fatty acid flotation is characterized by a wide divergence in methods, and attempts to define "common practice", even for the same type of mineral, are usually of little value because of the numerous exceptions. Such factors as desliming, pulp density, pulp temperatures, and reagents for conditioning are successfully employed under conditions representing almost extreme opposites. More precise control of variables is necessary than with sulphydric flotation processes It appears likely that variations result from independent development of a process from the multitude of variables that characterize fatty acid flotation and the ores of non-metallic minerals. Consequently, a symposium is a suitable way of presenting a summary of pretreatment methods for fatty acid flotation processes, together with froth control practices, as they exist today.

Jan 1, 1959

By Hitch M.

Many mining wastes, especially those from the metal mining industry, have traditionally been treated as a matter of little or no value and in practice a cost burden. Some wastes, due to their reactivity characteristics, have emergent values that go beyond purely economic and into the environmentally beneficial realm. This paper discusses the changing paradigm of mine waste management. Such fundamental parameters such as cut off grade, and strip ratio, are positively impacted by the revaluation of waste rock material. Mine rock waste can now be seen as a commodity of value, similar to the underlying ore being mined and influences the economic performance of suitable projects. This valuable material can be used for industrial purposes including acid neutralization as well as the capture and long-term disposal of anthropogenic carbon dioxide. The Turnagain Nickel project, located in northern British Columbia serves as an example of how waste rock material can become an important matrix for carbon capture and sequestration and can benefit economically from it. By producing material that has emergent economic value as well as carbon capture and sequestration capabilities, the sequestration matrix producer is a beneficiary of new carbon credits that have a market value and is looked upon favourably by regulatory authorities and affected stakeholders.

Jan 1, 2010

By B. N. Conley, K. D. Luxbacher

"The underground coal mining industry in the United States has recently seen the occurrences of several high profile, multi-fatality events. The explosions that occurred at the Sago Mine in 2006, the Darby Mine in 2006, and the Upper Big Branch Mine in 2010 have caused a ripple in an otherwise steadily improving safety record. These events transpired in the midst of an unprecedented level of government regulations and modern safety technologies. The recent increase in fatal events in conjunction with a minimal decline of both fatal and non-fatal injuries over the past decade may signify that current safety practices have reached a level of diminishing returns. Risk management, a safety approach that has been successfully applied in various industries including mining across the world, may provide a means to surpass the safety plateau in the U.S. RISKGATE is an Australian risk management program for mines that shows great potential for application in the U.S. However, fundamental differences between the coal mining industries in Australia and in the U.S. prevent direct implementation. This paper discusses aspects of the RISKGATE body of knowledge that require some adaptation before this program may be applied to the U.S. mining industry. INTRODUCTION The underground coal mining industry in the United States has recently seen the occurrences of several high profile, multi-fatality events. These events transpired in the midst of an unprecedented level of government regulations and modern safety technologies. The recent increase in fatal events in conjunction with a minimal decline of both fatal and non-fatal injuries over the past decade may signify that current safety practices have reach a level of diminishing returns. In order to combat this stagnation in performance, a modification to the manner in which the mining industry approaches worker safety may be warranted. The implementation of a risk management based approach presents a potential method for not only surmounting the current safety plateau but also for achieving the long desired objective of zero harm. RISKGATE a risk management body of knowledge designed for the Australian mining industry that shows great potential for application in the U.S. This paper discusses aspects of the RISKGATE body of knowledge that require adaptation before implementation in the U.S. mining industry. These adaptations are based on differences in operating practices and governmental regulations. This discussion will focus on the three major U.S. risk areas of explosion prevention, ground control, and moving equipment."

Jan 1, 2015

By Randal J. Barnes

Computer based techniques for solving the Ultimate Pit Limit Problem have appeared in mining literature since the early 1960's. The majority of papers pertaining to this subject can be partitioned into one of two categories: discussion of the pros and cons of a particular algorithm, or a case study presenting specific applications of an algorithm. Subsequently, there has a1 so been considerable debate concerning the best techniques between, essentially, two camps: those favoring the moving cones techniques, and those favoring the techniques which yield true optimal pit designs. The purpose of this paper is not to add to this debate, but rather to present a few new ideas (partially a new look at an old idea), which can be easily implemented to noticeably improve any ultimate pit limit approach independent of the particular algorithm used. These ideas fall under the heading of "bounding the optimum" (Barnes and Johnson, 1980).

Jan 1, 1982

By Emily Sing, Ashim Gajurel, Thomas Pennington, William Brown

The Pardee Chemical Feed Shaft Project involves construction of two new chemical feed shafts to improve raw water treatment capabilities at the East Bay Municipal Utility District’s (EBMUD) Pardee Reservoir in Valley Springs, California. The project includes construction of two 250-foot deep, 16-inch diameter stainless steel chemical feed shafts that penetrate an existing 8-foot diameter concrete lined conveyance tunnel. The design approach required the shafts be installed using top-down drilling methods and within a strict verticality tolerance (0.1%). Innovative precision drilling techniques ensured that the shafts penetrated the tunnel in their planned locations and the installed chemical feed lines would function as designed. Challenges included extremely limited access to the tunnel because of a requirement to maintain the tunnel in service during construction. This paper discusses the overall project’s design and construction approach, including unanticipated conditions that the project team faced and how these conditions were managed and overcome through collaboration between the contractor, designer, and owner.

Dec 1, 2022

By R. L. Grayson

Following lip on a USBM-sponsored research project, the authors have utilized the knowledge-base structure and system concepts from the Sun Sparcstation-based worker scheduling system of the Mine Management Support System to develop a PC-based application. The new software adopts the nested-window concept to facilitate data collection and modification on personnel, their availability on a shift, and work priorities for a shift as well as to allocate manpower optimally on a work shift and delineate supervisory training responsibilities. The various components of the software are described in detail, along with enhancements made to the original system.

Jan 1, 1996

By A. Moergeli, Philip Sander, John Reilly

"SUMMARY While the basic elements of risk management, including probability, consequences, risk registers, mitigation measures, etc., are now well understood, the process to include correlation, dependencies and linkage of risks and risk scenarios is less well defined and not well understood. To perform accurate and complete risk analysis and risk management, it is necessary to include correlation, dependencies and linkage between risk events, as well as risks that may occur multiple times. In this way, owners and contractors can more accurately determine risk-based costs, risk impacts and risk mitigation strategies. This paper will outline methods to deal with correlation, dependencies and linkage and will consider risks that may occur multiple times. Practical result comparisons – with or without these elements – will be presented. INTRODUCTION We believe the reader is familiar with basic concepts of risk, risk management and mitigation and the use of probabilistic cost-risk processes versus deterministic ones (Reilly et al. 2015; Sander et al. 2015). The probabilistic approach, compared to the simpler and more common deterministic approach (unit prices times unit costs plus a contingency), offers more useful information with respect to the range of probable cost as well as cost “drivers” and better quantifies the effects of risks, opportunities and variability – which improves understanding, leading to a better potential for profit (or loss) for contractors and added value for owners. In this context, a valid and sufficient quantification of correlation, dependencies and linkage of risk events, plus the impact of risks that may occur multiple times, is essential. Components of Cost Estimates – Base Cost, Risks and Other Uncertainties The components of cost that need to be correctly addressed in an estimate include (Moergeli et al. 2015): •,Base costs – the costs that will result if “all goes according to plan” (Reilly 2004) •,Risk costs – the resulting costs of threat and opportunity events, if they should occur •,Escalation costs – costs resulting from normally expected inflation with variability •,Other uncertain costs – costs that result from other events, normally external to the project team’s control, which may include unanticipated events, politically related changes and “black swan” events (Talib 2007)"

Jan 1, 2016

By S. K. Kawatra, S. K. Valluri, S. J. Root

Common carbon dioxide capturing reagents, such as amines and sodium hydroxide, are expensive, toxic, and energy intensive to regenerate. We have added frothers to a sodium carbonate solution in order to increase the surface area available for CO2 transport within the packed bed of a counter current scrubbing column. Addition of frothers has improved the performance of sodium carbonate scrubbing solutions to be on par with sodium hydroxide scrubbing solutions. This novel enhancement of a relatively inexpensive CO2 capture-regeneration cycle shows potential to allow plants to turn a profit by sequestering a waste product. These results are discussed in detail in the following manuscript. INTRODUCTION The combustion of fossil fuels converts chemical energy to thermal energy. CO2 is produced as a byproduct of the reaction. 80% of the world’s electricity is produced by using this thermal energy to power a generator, accounting for 40% of global carbon dioxide emissions. In an effort to stabilize the rising atmospheric CO2 levels, researchers are investigating the application of carbon capture and storage (CCS) systems in power plants. [1] Efforts to capture CO2 at some power plants have been successful, but the cost of installing and operating the required equipment is high. As such, very few power plants have CCS systems. If CO2 can be captured and processed into a product that can be sold at a profit, installing CCS systems in power plants will be a very attractive business decision. In order for the sale of captured CO2 to become a profitable venture, the cost of capturing the CO2 from a flue gas must be reduced. BACKGROUND The most common method for separating CO2 from a flue gas is by passing it through a counter-current packed bed scrubbing column. The flue gas enters the bottom of a column while a solution of a chemical with properties advantageous to the absorption of CO2 is pumped to the top. The fluids interact in a packed bed, where the CO2 is transported from the gas to the liquid. CO2 is an acid gas, so it is common for the scrubbing solution to be alkaline in nature in order to neutralize the carbonic acid that is formed when it is dissolves into water. The exhaust exits the top of the column free of carbon dioxide, which exits the column in the scrubbing solution, reacting or complexing with the absorbent. Figure 1 is a schematic drawing of a CO2 scrubbing column. It shows the molar flowrates and compositions of the gas and liquid at the bottom [1], the top [2], and an arbitrary height in the column [Z]. [2,15] L is the molar flowrate of liquid at any point in in the column. G is the molar flowrate of gas at any point in the column. Since the CO2 is transported from the gas to the liquid, L and G are variable with respect to height. To simplify calculations, the CO2 free molar flowrates Ls and Gs are often used. X is the fraction moles of aqueous CO2 per mole of CO2 free liquid. Y is the fraction moles of gaseous CO2 per mole of CO2 free gas. Figure 2 is a composition diagram of the scrubbing column depicted in figure 1.

Jan 1, 2019

By JA Vallejos

High stress underground mining poses a significant challenge to rock mechanics and rock engineering. To overcome theses challenges significative improvements in solutions and best practices of the design and operation of mines under high stress have been developed and implemented. This paper presents certain topics related to the management of high stress for sustainable underground mining. The topics include; the effect of preconditioning techniques (destress blasting and hydraulic fracturing) in the seismic rock mass response to underground mining and the dynamic behaviour of rock support systems. The opportunities associated with research in rock mechanics and practical rock engineering are discussed.

Apr 26, 2022

By H. Wagner

INTRODUCTION One of the most important tasks facing the opera¬tors of deep-level gold mines is supporting the roof strata in the immediate vicinity of the stope faces. Some of the deeper gold mines operate at depths ex¬ceeding 3.0 km; the extreme mining depths and the tabular nature of the gold-bearing reefs result in high stress concentrations at the abutments of the stope faces. These, in turn, lead to extensive fracturing of even the hardest quartzites. Although most of these fractures develop in a stable manner, there have been many instances where rock failure occurred suddenly, resulting in a considerable amount of damage to the underground workings. Such violent rock failures commonly are known as "rock bursts," and they are typical of many hard-rock mines that are operating at great depths. To safeguard mining personnel and equipment against the effects of stable and unstable rock failures, adequate support must be provided to the fractured roof as quickly and as effec¬tively as possible. Traditionally, timber props and timber packs have been utilized to provide roof support in gold mine stopes up to 1.5 m wide. Both methods of support suffer from the fundamental disadvantage of generating sup¬port only in reaction to movement of the strata. Since unrestrained strata movement often results in a break¬down of the frictional forces that preserve the stability of the intensely fractured roof strata, it is essential that stope supports have rapid load-bearing characteristics. An equally important requirement is that the roof sup¬ports be able to accommodate displacements of the rock mass. A third requirement of roof supports in gold mine stopes is that they must be able to accommodate the high rates of stope convergence typical of rock bursts. The hydraulic prop is the obvious choice for sup¬porting the stope faces in deep-level hard-rock mines. Since hydraulic props can be installed with a positive setting load, they can provide roof support that is independent of strata movement. By equipping the hydraulic props with yield valves, they meet the require¬ment of being able to accommodate rock-mass displace¬ments. However, the requirement of being able to accommodate high rates of stope convergence without overloading or damaging the rock strata was rather difficult to meet. The first introduction of hydraulic roof supports into gold mine stopes showed that conventional hy¬draulic props, such as those used in coal mines, were completely unsuitable for a number of reasons, in¬cluding: 1) Since drilling and blasting are used to break the ore in gold mine stopes, supports installed close enough to be effective are exposed to the vigor of the blast. Conventional coal-mining props suffered extensive blast damage, despite being protected by a blast barricade. 2) The environmental conditions in gold mine stopes favor corrosion. The high quartz content and the abrasiveness of the ore further aggravate the problem by damaging the protective coatings on the hydraulic surfaces. Simply changing the design of gold mine props to have the piston project from the bottom rather than from the top resulted in dramatic improvements in the service life of the props. The improvement was attributable to external water in the stope washing the fine quartz grit away from the hydraulic surfaces, rather than concentrating the particles between the cylinder and piston of the prop. 3) The most obvious deficiency of conventional coal mining props was their inability to yield rapidly enough to accommodate the high convergence rates of rock bursts without overloading the supports. As a result of the first disappointing results with hydraulic supports in narrow hard-rock stopes mined by drilling and blasting, a comprehensive research and development program was undertaken. The hydraulic props resulting from several years of research and exten¬sive field trials are described herein. To date (1978), more than 130,000 of these props have been manufac¬tured and used successfully in a number of mines and under a variety of geological conditions. Although many of the detailed specifications are directed spe¬cifically to gold mining conditions, there are a number of points that are of general importance in the design of underground support systems for tabular excavations in hard-rock mines of any type. SPECIFICATIONS FOR RAPID-YIELDING PROPS Yield Requirements The yield requirements for hydraulic props in deep¬level hard-rock gold mines are summarized in the fol¬lowing paragraphs. Slow Yield Load: The design of the yield valve must allow the yield load to be preset to between 300 and 400 kN. This flexibility is necessary to account for the differences in the strength properties of the roof and floor strata. Drop in Load Under Slow Yield: The drop in sup¬port load during a slow yield should be as small as possible, but it should not exceed 5% of the slow-yield load. Rapid-Yield Load: The load exerted by the prop during periods of rapid stope convergence should be as close as possible to the slow-yield load. The rapid-yield load should not exceed the slow-yield load by more than 15% at yield rates of 1.0 m/s. The limitation of the upper valve of the yield load is important; it deter¬mines the hydraulic performance of the yield valve. The hydraulic props that satisfy this criterion have performed well, even under severe rock bursts. Load Changes Under Rapid Load: On some of the earlier rapid-yielding props, conditions of dynamic in¬stability were observed; these conditions resulted in a complete breakdown of support resistance. It is essen¬tial that the force oscillations during rapid yielding be as small as possible, not exceeding -*5% of the average rapid-yield load at a yield rate of 1.0 m/s. Longitudinal Resilience: During rock bursts, vibra¬tions of the roof and floor sometimes are observed. To

Jan 1, 1982

By W. D. Mayercheck, A. G. Mayton, J. R. Bartels

Since 1982, the US Bureau of Mines has investigated improvements in protection for operators of thin seam shuttle cars. Due to working height restrictions in thin seam mines (=1.22 m or 48 in.). Federal mine regulations require that canopy protection on shuttle cars be provided only in mines =1.07 m (42 in.). However, court obtained variances are granted to mines =1 .22 m (48 in). This paper presents ongoing research to design and evaluate a uniquely positioned, ergonomic compartment for a shuttle car that provides the operator with full canopy protection in working heights of 1.02 m (40 in.).

Jan 1, 1990

By S. W. Cavender

The analysis of the results of metallurgical experiments is often complicated by experimental errors and uncertainty, the complexity of the system being studied, and the confusion of correlation with causation. Consequently, comparative statistics are used to determine if a difference exists between the outcomes of tests, an estimate of this difference, and the precision of the estimate. This paper reviews the use of significance tests and confidence intervals for the comparison of results from two tests, the use of reference distributions, and blocking and randomization techniques to reduce unavoidable sources of variability. These techniques are demonstrated using plant and laboratory data.

Jan 1, 1993