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By J. G. Manchuk, M. Thurston

"The degree of uncertainty associated with a natural diamond resource is important to quantify from the time of discovery through the production lifetime. Data collection occurs during the discovery, exploration, delineation, and production or recovery phases. Quantifying the relationship between data and uncertainty is an important component of project valuation. The value of data is measured as their potential to reduce uncertainty if they are collected. A method is developed using Monte Carlo simulation for predicting resource uncertainty and valuing data during critical phases of development, particularly discovery and exploration. The technique is applied to diamond pipe deposits.RÉSUMÉ Il est important de quantifier le degré d’incertitude associé à une ressource diamantifère naturelle, depuis le moment de sa découverte et durant toute la durée de l’exploitation. La collecte de données se fait durant les phases de découverte, d’exploration, de délimitation, et de production ou de récupération. La quantification de la relation entre les données et l’incertitude est une composante importante de l’évaluation du projet. La valeur des données est mesurée en tant que leur potentiel à réduire l’incertitude si elles sont recueillies. Une méthode a été développée qui utilise la simulation de Monte Carlo pour prédire l’incertitude de la ressource et évaluer les données durant les phases critiques du développement, surtout celles de la découverte et de l’exploration. La technique est appliquée à des gisements de cheminées diamantifères."

Jan 1, 2015

By W. E. Stumpf

"SynopsisSouth Africa recently announced a resurgence in its commercial nuclear power programme. The implications for the development of the necessary high-level manpower within South Africa’s tertiary educational system and its national research and development (R&D) capacity in materials science and engineering, as well as in other engineering disciplines, are placed into perspective. An organized national process of developing this manpower by moving away from the previously high-risk and costly ’large programmes’ to rather a selection of ‘small and better’ research projects and a redefinition of what constitutes ‘nuclear materials’ are proposed as parts of this strategy.IntroductionSince 2008, and more particularly in 2014/2015, South Africa has woken up to the fact that significant steps need to be taken to ensure sufficient electricity generating capacity for the future, even beyond the coal-fired stations at Medupi and Kusile currently under construction. It is, therefore, encouraging to see some active large-scale wind farms in the Eastern Cape near Jeffrey’s Bay, in the Couga area, and others in the Western Cape already in operation. In addition, many solar energy projects are also progressing from the small localized scale to larger programmes in the Northern Cape, which may contribute some capacity on a national basis. South Africa needs to tap into its renewable resources of wind and solar much more, but will these projects solve the country’s long-term industrial needs? Unfortunately not. One cannot run mines and trains on solar cells. Industry needs reliable baseload capacity, and with very limited easily accessible hydrocapacity this leaves really only coal, possibly natural gas, and nuclear power as options. South Africa’s current over-reliance of about 90% on coal–fired power, however, places it in an internationally vulnerable position, and diversification into a more equitable energy mix should be a national priority for the medium to long term. South Africa cannot significant climate change confronting the human race, as the IPCC cautioned in 2013, and will have to adjust its future energy reliance to a more balanced combination of sources."

Jan 1, 2015

By A. G. Nitschke, I. Ossenbühl, W. Dolsak, J. Dase

"The authors have successfully developed an innovative rehabilitation concept, which meets actual technical standards and minimizes the impact on the operation of a key conveyor tunnel. A flexible and stepwise ground support rehabilitation program utilized a combination of yielding steel arch sections with grout filled fabric hoses, which represents a fast and safe backfilling support system. The system was developed and successfully installed at Bingham Canyon Mine, the world’s largest open pit copper mine, which also includes numerous underground structures. The mine is owned and operated by Kennecott Utah Copper (RTKC) a fully owned subsidiary of Rio Tinto. The system was implemented at a conveyance tunnel, which was originally designed as a railroad tunnel, but was re-commissioned and is currently used as a conveyor belt tunnel to transport ore from the open pit to processing facilities outside the mine. The existing structure showed signs of overstressing due to movements in the surrounding rock mass, which had to be addressed with a yielding support system in order to provide safe access into the tunnel. However, the impact on the conveyor belt operation due to support installation was to be limited to the bare minimum. Keywords: rehabilitation, yielding support, mining, stabilization, and grout filled fabric hose.PROJECT DESCRIPTION The C6 Tunnel is considered a critical asset for the operation of the Bingham Canyon mine as it comprises the standard route for transporting crushed ore from the open pit to the processing facility on a continuous conveyor belt system. The C6 tunnel was originally built as a railroad tunnel. Construction was completed in 1959. The original horse-shoe shaped cross section of the tunnel was 18 feet wide and 24-1/2 feet high [8]. The tunnel length was approximately 18,000 feet. During its service life, the railroad tunnel has undergone several transformations. The length of the tunnel towards the Bingham Canyon pit was shortened over the course of mining operations and the railroad tracks in the tunnel were removed. The invert was partially backfilled (3 feet typical) and a 72 inches belt conveyor was installed. Currently, the C6 Tunnel is nominally only approximately 21 feet high and 15,000 feet long. Ground Support and Rehabilitation Measures prior to 2014 The C6 tunnel was mined mainly with conventional mining methods, using drill & blast as the typical one. However, the weak geological sections, such as those encountered in the Fortuna fault, were excavated by shaping and chipping with machine-held moils [8]."

Jan 1, 2015

By M. K. Larson

"Specialized numerical modeling codes have been developed over the years to estimate ground stresses during the excavation of coal in underground mines. One of these tools, MULSIM, a displacement discontinuity boundary element code, was last developed by Zipf into a version called MULSIM/NL [USBM 1992a, 1992b]. The code was used frequently in years past, but closure of the Bureau of Mines in 1996 marked the beginning of a pause in its development. A similar tool with distinctly different treatment of overburden idealization, LaModel, was subsequently developed [Heasley 1997] and largely displaced MULSIM/NL in the literature. However, recent work modeling deep western longwall coal mines [Larson and Whyatt 2013] has demonstrated that MULSIM has distinct advantages for regions with relatively stiff and strong overburden. This work required that MULSIM be revived and updated into a version called MulsimNL/Large. Updates include larger array sizes, greater precision, greater number of materials, and the addition of a five-point, six-segment pillar load/displacement model that provides the user a more flexible coal-strength model allowing hardening and softening before a final residual strength. MulsimNL/Large has the ability to calibrate to large load transfer distances observed in some western U.S. coal mines that appear to be caused by strong, massive units in the overburden and/or floor of a coal mine. Also, it provides the ability to calibrate gob stiffness to simulate measurements or estimates of overpanel weight distribution between gob and abutment, while still maintaining load transfer distance with minor adjustments. MulsimNL/Large can easily implement material strengths calculated from various pillar strength models. The five-point model gives MulsimNL/Large the ability to easily simulate pillar behavior that is extracted from detailed pillar models, such as FLAC3D. MulsimNL/Large or similar approaches should be considered for evaluating mining layouts where stratigraphic conditions are known to cause overpanel weight to transfer to an extent significantly longer than the empirical method widely used to calculate load transfer distances in the U.S. [Peng and Chiang 1984; Mark 1987; USBM 1990]."

Jan 1, 2015

By S. X. Shi, M. Tan, Y. Q. Li, D. F. Han, Z. B. Han

Bauxite resources in China are mainly diaspore ore with the characteristics of low ratio silicon to aluminum. In order to obtain high quality of alumina product, flotation process is generally used to extract the aluminum from diaspore ore. Small aeration rate is needed for bauxite flotation, which requires air to be controlled accuracy. In addition, productive froth from bauxite flotation is too sticky to effects froth transportation. Air-forced XCF/KYF flotation machines are helpful for aeration control, while self-suction GF flotation machines benefits froth transportation. Zhongzhou aluminum plant of China Aluminum Group (Chinalco) uses 7 series of XCF/KYF /GF combined flotation machines to process bauxite. Air distribution, suspension characteristics, froth flow velocity and Al2O3 recovery were investigated, to evaluate the performance of flotation machines in one series and determine recovery contribution of each cell to the entire flotation circuit.The air distribution degree varies from 3 to 4, which is enough for bauxite floatation process. Froth in the tank could flow smoothly with a flow velocity of 2.4m/min. The recovery of the first KYF-40 flotation cell is the largest. Flotation concentrate of Al2O3 is up to 64.29%, the total recovery is about 75%, and the ratio of Al/Si has reached 10.4.

Jan 1, 2015

By Xingkai Wang, Wenbing Xie

"To control the large deformation of soft rock around the roadway subjected to high stress, it is important to improve the stability of support structure, in addition to increasing support strength. In this study, the causes for the destabilization of U-steel frame and its loading characteristics were analyzed by theoretical analysis, laboratory experiments and field tests. The technology of constant support resistance, the principle of support structure compensation and the compensation technique are proposed. The results indicated that the main reasons for frame structure destabilization are caused by low strength of connector, irrational structure of connector, poor interaction between the surrounding rocks and support frame and structure, and unstable support structure. Thus, the corresponding technological measures, such as connector with high strength and rational structure are adopted. The bearing capacity of frame is unstable after slipping. In order to maintain the high support resistance when the frame is performing the support function, the frame connector should be retightened after slipping. Though the working resistance may be improved greatly by using the backfilling or back grouting of U-steel, the frame remains unstable because of the unstable frame structure. Therefore, according to the deformation characteristics of rocks surrounding the roadway and the structure instability of U- steel frame, the stable structure device is used to carry out the structural compensation of U-steel frame, and the whole bearing capacity of the frame and its structural stability are improved greatly.INTRODUCTIONThroughout the development of the roadway supports for coal mines in China, it can be seen that the supporting strength and supporting resistance increase continuously with increase in mining depth and supporting difficulties [1]. With respect to the ground control mechanism and supporting technology of rocks surrounding the soft rock roadways subjected to high stress, considerable research has been done both at home and abroad. The backfilling technology behind the high-resistance and yieldable U-steel wall, the new type of grout/bolt support technology and the bolting with high-strength mesh support technology were developed, and have been used widely in coal mines with notable economic benefits [2-7]. However, a large number of engineering practices show that in many cases the existing rock control technology of roadway may not control the large deformation of the soft rock roadways subjected to high stress. The reason that the large deformation of soft rock roadway occurs is mainly due to poor structure stability of existing frame bearing structure, not insufficient support strength."

Jan 1, 2015

By Chee Theng

"Mining professionals are a resilient lot. Sure, copper prices are dismal, permitting processes seem interminable and the top mining companies are shedding jobs like a Shetland sheepdog sheds hair. All the more reason to hone technical skills, reconnect with old contacts and get one’s finger on the pulse of the industry.More than 400 did just that in the balmy sunshine and among the saguaro cactus of the Tucson venue of the SME Arizona Conference.Giving the keynote speech was Patrick Merrin, vice president at Hudbay Minerals (see box), while the luncheon speaker was University Distinguished Professor Mary Poulton, director of the Lowell Institute for Mineral Resources at The University of Arizona.“Attendance was great, especially given the copper price,” said Ta Li, vice president of business development at Tetra Tech and 2001 SME President. “The luncheon speaker was one of the better ones in recent years. Her talk contained a lot of fresh ideas, and practical versus theoretical concepts.”Talk about values, not economicsPraise was unanimous for Poulton, who gave a thought-provoking talk on “The New Face of Mining: The Culture Change for Compatible Mining.” Corporate social responsibility has been embraced by the metals mining industry, and it’s being done right, she said. “So why do we have more conflict? Why are there more protests? Why does permitting take longer and longer?” Poulton made a case for an approach based on compatible, rather than sustainable, mining to present a new face of mining that can be compatible with communities, cultures and the environment, and still be profitable. When the mining industry starts to talk about compatibility between what it is doing and what “me,” as the consumer, wants, what “we,” as citizens of a community, want, and what’s good for the “world,” we’re going to see the next culture change happen, she concluded."

Jan 1, 2015

By W. Hermülheim, J. Brune

"This paper analyzes mine emergency management and rescue practices in German underground coal mines and compares them to those used in the United States. The German mining industry has developed these practices over more than 100 years, and they have successfully managed numerous fire, water inundation and ground control emergencies using these techniques. The authors interviewed German mine emergency professionals about rescue team and emergency operations. These operations were then analyzed to determine which of these German principles would be of interest to United States mine rescue teams. Implementing these programs into United States mine rescue and emergency operations was analyzed. INTRODUCTION Coal mining has become much safer industry than it has been in the past. Advances in safety and health regulations and company polices have improved working conditions for miners all over the world. Even with these advances there is still a need for continued attention to safety and health. It is also important for mine safety professionals to observe practices and procedures in other countries and cultures and learn what and how to apply this knowledge in their own systems. Coal mine rescue has been an integral part in improving coal mine safety. Mine rescue procedures have evolved with time, experience and technology development. Today, coal mine rescue teams are still needed and must be continually trained and prepared for any mine emergency. Although it is hoped that improved mine safety policies and practices will eliminate coal mine disasters in the future, accidents remind us that disasters can still happen today. In May 2014, Turkey experienced a severe coal mine disaster where 301 people were killed [G.Tuysuz, 2014]. Our industry must learn from these incidents, focusing on disaster prevention and making improvements in mine rescue operations. Mine rescue procedures differ from country to country due different regulatory environments and different historical evolution of emergency response. Sharing practices and procedures from one country to another enables learning from different experiences and cultural backgrounds. Sharing is also a way of preserving information, identifying and learning best practices."

Jan 1, 2015

By T. W. Camm

"As engineers, we are trained to use logical, rational problem solving to insure our mines operate at maximum efficiency. We tend to use the same technical approach to design safety into all mining systems. This works well for machines, but not so much for the human component. Recent insights in the field of behavioral economics provide useful ideas for addressing the fact that we are driven by emotions more often than by rational thought. Understanding the nonrational aspect of human behavior is an important piece of any safety system design. INTRODUCTION The most common economic model is based on humans making rational decisions; that given the proper information, we will make a logical, rational decision based on what is best for ourselves (Ariely, 2009, p. xviii). In many cases this is an accurate description of how we make decisions. As an engineer, I was trained to apply the precision of mathematics and logic to solve problems. As an engineering professor, I now teach this approach to bright young minds preparing them for a life of professional effectiveness as practicing engineers. That said, we are not only rational. Daniel Kahneman, winner of the Nobel Prize in Economics, describes a model for how we think (Kahneman, 2011). System 1 is the part of our mind that is fast, intuitive, and emotional; while our logical, slower, and deliberative mind is System 2. According to Kahneman’s model, System 1 runs automatically, most of what you think and do originates in System 1. System 2 takes over when things get difficult, including the application of math and logic, and the resolution (or avoidance) of conflict. As engineers, we would typically assume that we operate in System 2 mode most of the time. This is where the model becomes useful, for Kahneman points out two important aspects of the dynamic between the two systems in our mind. First, System 1 has biases, systematic errors that lead to answering questions with an easier answer (rather than a right answer) before System 2 is engaged. Second, we can be blind to the obvious, and also be blind to our blindness. Complicating things further, System 1 cannot be turned off (Kahneman, pp. 24-25)."

Jan 1, 2015

By S. K. Kawatra, J. A. Halt

"Low-grade iron ores are finely ground and processed to recover iron-bearing minerals. However, the iron-rich powder is too fine to be used directly in blast furnaces and most direct reduction furnaces, and must be agglomerated or pelletized into a usable product called “pellets.” Bentonite clay has traditionally been used as a binder to make iron ore concentrate pellets, but it is expensive and contaminates the pellets. Organic binders may be a viable alternative to bentonite clay. This manuscript reviews organic materials that have been used to make iron ore concentrate pellets. Included are discussions on the development of organic binders, common pros and cons to organic binder use, organic binder structure and its effects on agglomeration, and additives to organic binders.IntroductionIron ore agglomeration turns finely disseminated, low-grade iron ores into a usable product, called pellets. During pellet production, fine-grained, iron-rich minerals are liberated from low-grade ores, concentrated, and agglomerated into round balls that are thermally hardened or cold-bonded to form pellets. Pellets are then transported to blast furnaces or direct reduction operations where they are used to produce iron; iron is further refined and shaped into the wide variety of steel-based industrial and consumer products in use today.Over the years, pellet production has become increasingly more prevalent with the increased exploitation of low-grade iron ores and increased iron and steel consumption around the world. In 2010, world iron ore pellet production was 388 Mt. It could be argued that the current pellet production process has been enabled by the use of binders – practical experience has shown that it would be nearly impossible to agglomerate iron ore concentrates using rotary drums and discs without using a binder."

Jan 1, 2015

"History - How did you get into mining and involved with SME?Unlike many past presidents, I do not come from a mining lineage. I liked math in high school and believed I wanted to be an engineer. I told my math teacher that, and he laughed in my face. I believe that humiliation is what carried me through engineering school. At the time my ability to go to college relied on how inexpensive I could make it. My brother told me that there were a lot of scholarships in mining engineering, and I should apply to mining schools. As usual, he was right and I was off to the University of Idaho to study. My first summer break I got a job with Hecla at a mine in Arizona. I was a laborer on a shotcrete crew. I knew after the first summer that I loved underground mining, and I never considered changing disciplines. Looking back, I was working in miserable conditions (hot, humid), on a miserable job (shotcrete), where I got injured, and two summer student roommates died in a car accident on the commute home after work. I had every reason to hate the industry, as I had seen virtually everything bad about what we do. But I didn’t, I loved it. I said I was good at math, I never said I was smart.I joined SME in college because I was told to by the head of the mining school, Dr. Jack Hoskins. You did what Jack told you to do. I got involved because I went to an annual meeting and the papers in the underground sessions were terrible. I refer to bad papers as the “Tensile strength on cable bolts in sub-arctic regions on Tuesday” papers. Real snoring fodder. I don’t remember who I was complaining to, but they told me to quit my grumbling and fix it. So I chaired a session, and tried to get only good quality papers, something that has been my mantra for years with the Mining & Exploration Division. I also volunteered to help the local sections too. Then one day I woke up as president.What is your opinion of the health of the mining industry?The mining industry is in bad shape. Coal is under attack and will likely never recover to its former greatness. Our President has banned new coal leases, and the state of California is forcing people it does business with to divest their interests in coal companies. And that all happened in just in a few short weeks this January. Usually in America you get a trial before you are given a death sentence, but not with coal."

Jan 1, 2015

By F. Baczek, S. S. Rocks, D. Chaiko, T. Walters

The atmospheric leaching of chalcopyrite concentrates using acidic ferric sulfate lixiviants is well known to suffer from slow leach kinetics and poor copper recoveries. A number of approaches have been proposed for improving both leach kinetics and recoveries in this system. Many of these, while effective, suffer from high CAPEX and/or OPEX. As many mine sites begin transitioning from heap leaching of copper oxides to processing of primary copper sulfides, cost-efficient leach processes that are compatible with existing SX/EW processes will be needed to maintain existing cathode production. To this end, FLSmidth is exploring process options and reactor technology for the hydrometallurgical processing of primary sulfides. One approach that appears to be highly effective at increasing copper recoveries takes advantage of the enhanced reactivity of transitory, surface-defect structures generated during particle fracture. Significant process efficiencies are gained by matching the rate of grinding to the rate of electrochemical leaching in Mechano-Chemical leach processes. The patent-pending FLSmidth® ROL process uses a Stirred Media Reactor (SMRt reactor) to achieve copper recoveries of 97+% in 6 hours or less. This approach overcomes many of the surface passivation problems that have hindered other atmospheric leach processes. New insights to leach mechanisms are presented.

Jan 1, 2015

By T. Shumka, M. J. Druckenmiller

"INTRODUCTION As we push further into the 21st century and closer to a more efficient mine, safety and operational enhancements are the two major keys towards attaining success. The Crusher Vision Automation System (CVAS) is a technological advance that will allow an operator to achieve higher safety and higher operational goals in the same piece of equipment. The CVAS is a patent pending system and method for measuring and maintaining the closed side setting (CSS) on gyratory crushers. In the same equipment and technology package, the CVAS will also allow safer placement of main shaft pieces for maintenance and replacement. This technology yields multiple uses and allows a site to significantly enhance safety and operational efficiencies. This measurement technique is used to provide more accurate data and faster data collection times than current techniques used today. It will give crusher operators accurate and reliable measurement for the CSS in a live, operating environment. Measurement data can be collected in five minutes allowing for fast adjustment of the mantle position and subsequent enhancement and streamlining of a crusher and downstream flowsheet. The advantage of this system is that it is permanently mounted at the crusher location, where the operator can turn the system on and off as many times as they like throughout the day with a goal of maintaining a constant CSS gap based on production and maintenance criteria to help streamline operations and enhance safety efficiencies.Regarding its other main functional area, mainshaft maintenance, it allows this work to be performed remotely while keeping personnel safer and out of harm’s way. SAFETY ENHANCEMENT The safety factor enhancement with this system is extreme. It does not require the use of overhead cranes, cleaning out the crusher, lowering people into the crusher or having the operator lower paint cans or lead balls into the crusher pocket while the crusher is in operation for measuring the setting. In order to perform the CSS measurements, the operator only needs to operate the laser through manipulation of a joystick while watching the video feed. Danger of a person falling into the crusher while trying to take measures is eliminated, as are the effects of handling lead balls and tracer dyes."

Jan 1, 2015

By B. Yu, S. Kelebek, C. Gibson, M. Aghamirian

There are a number of high grade niobium deposits worldwide which have been deemed untreatable by flotation due to the very fine grained nature of the in situ pyrochlore, the primary niobium bearing mineral. A known method of recovering extremely fine particles is through the use of chelating reagents such as hydroxamic acids which have a strong affinity for transition metals. However, one of the major issues in the flotation of niobium bearing minerals using hydroxamic acids is the corresponding recovery of other transition metal gangue minerals including magnetite, hematite, and pyrite. In order to better understand the differences in behavior of niobium and iron bearing minerals in flotation with benzohydroxamic acid (BHA) and sodium hexametaphosphate (SHMP) at a range of pulp temperatures, a Box-Behnken experimental design was employed. Regression models for the global recovery of iron indicated that iron mineral recovery was significantly influenced by both BHA and SHMP dosage. Upon examinination of flotation products by semi-quantitative XRD, it was observed that recovery of iron oxide and sulphide minerals (hematite, magnetite, goethite, and pyrite) was problematic at high benzohydroxamic acid dosage, while sodium hexametaphosphate was mainly helpful for carbonate mineral depression. Iron rich carbonates (likely an iron rich dolomite) largely reported to the tails with increased SHMP dosage.

Jan 1, 2015

By M. D. Evans

"Note: The views expressed herein are those of the author, not of the Government of CanadaThe mining industry has a significant opportunity to capitalize on past learnings to build better social relationships. The industry’s relationship with society is critical and under pressure. Rising levels of public opposition and social conflict are already having material impacts on operations around the world. The industry has an opportunity to shape the future direction of this social engagement, build public trust, and proactively respond to a material risk to operations, but first it needs to better understand the nature of the challenges and the urgency of addressing them.RÉSUMÉ L’industrie minière a actuellement une excellente occasion de tirer profit de ses expériences antérieures pour établir de meilleures relations sociales. Les relations entre l’industrie et la société sont critiques et elles subissent de grandes pressions. L’escalade de l’opposition par le public et les conflits sociaux ont déjà des impacts physiques sur les opérations partout à travers le monde. L’industrie a l’occasion de façonner la future direction de son engagement social, d’accroître la confiance du public et de répondre de manière proactive à un risque matériel aux exploitations, mais elle doit tout d’abord mieux comprendre la nature des défis et l’urgence de les traiter."

Jan 1, 2015

By S. R. Dindarloo

"Truck-shovel systems are the dominant material loading and haulage machinery in open pit mining operations. Optimal selection, sizing, and allocation of this capital intensive equipment is highly desirable for both achieving production targets and improving the mine’s economics. In this study, discrete event simulation technique was applied for modeling material transportation in Golegohar open pit iron ore mine in Iran. Direct observation of the material loading and haulage for duration of three months resulted in statistical modeling of the operation in the form of probability distribution functions. These probability models were used as the inputs of a stochastic simulation model constructed in GPSS/H simulation language. The model was validated through comparison with the actual operation and was used to test different what-if scenarios and sensitivity analysis of the current system. Some modifications in the number of trucks, shovels, and dispatching strategies were proposed. Simulation resulted in considerable improvements in the mine’s production and economics.INTRODUCTION There are three different mechanisms of discrete, continues, and hybrid material transportation in open mines, including but not limited to: i) in-pit crusher and conveyor belts (hybrid), ii) slurry piping (continues) and iii) truck-shovel system (discrete). Although, each mechanism has its advantages, the truck-shovel system is the dominant method of material loading and handling in open pit mines owing to its high production rate, excellent flexibility, relatively low operating and capital costs, and good maintainability. General objectives of optimal equipment selection include: i) meeting the long and short term requirements of production rates, ii) human & equipment safety, iii) environmental protection, and iv) economic operations (Figure 1).The two most important decision factors on a truck-shovel system selection and sizing are the equipment geometry and size. Geometry (equipment width, weight, turning radius, swing angle, etc.) is mostly controlled by mine’s designs and layouts, as well, as operational constraints. After selection of a favorable geometry based on the constraints; the next step is to select the equipment manufacturer. Once the geometry and manufacturers are selected; the next step is to decide on models (e.g. Bucket size) and required number of each unit"

Jan 1, 2015

By Ihsan Berk Tulu, Michael Sloan, Ted Klemetti, Michael M. Murphy, Gabriel S. Esterhuizen, Jame Sumner

"In this paper, the advantage of using numerical models with the strength reduction method (SRM) to evaluate entry stability in complex multiple-seam conditions is demonstrated. A coal mine under variable topography from the central Appalachian region is used as a case study. At this mine, unexpected roof conditions were encountered during development below previously mined panels. Stress mapping and observation of ground conditions were used to quantify the success of entry support systems in three room-andpillar panels. Numerical model analyses were initially conducted to estimate the stresses induced by the multiple-seam mining at the locations of the affected entries. The SRM was used to quantify the stability factor of the supported roof of the entries at selected locations. The SRM-calculated stability factors were compared with observations made during the site visits, and the results demonstrate that the SRM adequately identifies the unexpected roof conditions in this complex case. It is concluded that the SRM can be used to effectively evaluate the likely success of roof supports and the stability condition of entries in coal mines.INTRODUCTIONSince the introduction of roof bolts in the coal mines during the late 1940s and 1950s, roof bolts promised to dramatically reduce roof fall accidents (Mark, 2002). However, ground falls still remain a significant factor in underground coal mine injuries and fatalities. In 2013, ground falls accounted for 4 of the 14 fatalities and 166 of the 1577 reported lost-time injuries in underground coal mines (MSHA, 2015).The design of appropriate support systems requires the understanding of: 1) the variable nature of the rock mass, 2) the performance and characteristics of the roof support, 3) the interaction between the rock mass and the installed support system, and 4) the in-situ and mine-induced stress distribution around the excavation. Over the past 25 years, multiple design approaches have been used in coal mine ground control. The approaches include empirical mechanistic methods, empirical statistical analysis, rules of thumb, and numerical methods (Hebblewhite 2006). In the U.S., Analysis of Roof Bolt Systems (ARBS) can be given as an example of an empirical method. ARBS uses relatively simple equations to calculate the intensity of support provided by a roof bolt system and compares it with a suggested ARBS value (Mark et al., 2001). The suggested ARBS design equation is derived from an analysis of 100 case histories. The ARBS design equation is dependent on two parameters: depth of cover and Coal Mine Roof Rating (CMRR). More recently, a probabilistic design approach was developed by Canbulat and van der Merwe (2009) in South Africa. In this method, the variability of the rock mass, the mining geometry, and support characteristics are included in the analytical models. The major advantages of these two methods are: 1) they can be applied rapidly and easily, 2) complex rock mass/ roof support interaction mechanisms are represented with simple equations, and 3) they are supported by large databases. However, both methods generally ignore mining-induced stress distribution, details of the roof support system, details of the geological setting, and the interaction between the support system and the rock mass."

Jan 1, 2015

By Michael J. Castner

"INTRODUCTIONMultiple-seam mining is an ever growing concern for engineers and mine management in every portion of the mining industry and is especially true for coal mining operations. The goal of this report is to identify the location and severity of multiple-seam interactions, provide AMSS calculations performed on the worst of these locations, and follow up with a visual examination of the underground physical effects on the roof and ribs in the locations identified for analysis. Multiple-seam mining is increasingly being studied because:1. Multiple-seam mining can create a multitude of problems such as roof falls, pillar crushing, pillar failing, rib spalling, floor heave, and inundation of water, gas, or oxygen-deficient air that can disrupt mining operations and threaten the safety of the miners.2. Multiple-seam mining is becoming more prevalent due to the depletion of virgin coal reserves.Currently, coal mining in the United States has progressed to the point that a growing number of mining companies are operating in coal seams located above, below, and/or adjacent to previously mined out coal seams. As a result, the state and federal governments are enacting higher safety standards on mining operations. For example, in years past, pillars may have been properly designed to handle single seam interactions for a particular mine or mines; however, today, where mining is now being considered above or below a previously mined area, these loading conditions may not be adequate to handle the removal of additional seams above or below the previously mined reserve. Studies from 1981 estimated that two-thirds of the mineable coal reserves in the United States would be impacted by multiple-seam implications. Today, over three decades later, it is obvious that most of the remaining mineable coal reserve will be influenced by previously extracted seams. Thus, thefocus on multiple-seam mining interactions on current and future mining operations. In 2012, underground mining in the United States produced 342,287 thousand short tons of coal. Northern Appalachia accounted for over 30% (103,301 thousand short tons) of this total (U.S. Energy Information Administration, 2013). Rosebud Mining Company and Western Allegheny Energy (RMC and WAE) have a combined total of 23 actively producing underground mining operations and at least four new mines under or ready for development. All of these mines are located in coal seams (Upper and Lower Freeport; Upper, Middle, and Lower Kittanning) of northern Appalachia (Pennsylvania and Ohio). Currently, more than half of the RMC and WAE mines are dealing with multiple-seam interactions. Seven mines are undermining previously mined out coal seams, and five mines are overmining previously mined out coal seams. Also, between these companies, five mines have inner-seam sloping possibilities (2 completed, 3 planned), most of which will result in mining over or under previously mined areas."

Jan 1, 2015

By Gabriel S. Esterhuizen

"Cable bolts are sometimes used in low-seam coal mines to provide support in difficult ground conditions. This paper describes cable bolting solutions at two low-seam coal mines in similar ground conditions. Both mines used support systems incorporating cable bolts as part of the primary support system. Two original cable bolt based support systems as well as two modified systems are evaluated to estimate their ability to prevent large roof falls. One of the support systems incorporated passive cable bolts, while the other used pre-tensioned cable bolts. The results and experience at the mines showed that the modified systems provided improved stability over the original support systems. The presence of the cable bolts is the most important contribution to stability against large roof falls, rather than the details of the support pattern. It was also found that a heavy steel channel can improve the safety of the system because of the ‘sling’ action it provides. Additionally, the analysis showed that fully-grouted rebar bolts load much earlier than the cable bolts, and pre-tensioning of the cable bolts can result in a more uniform distribution of loading in the roof.INTRODUCTIONCable bolting is sometimes used as primary support in coal mines experiencing difficult roof conditions. In low-seam mines the flexibility of the cable bolts allows greater length supports to be installed near the advancing face without the use of couplers. When used as primary support, the cables are typically installed in the same row as fully grouted bolts, replacing two or more of the bolts in each support row. A heavy steel channel may be used as a strap to spread the support load over a greater portion of the roof. Historically, the Mine Safety and Health Administration (MSHA) has not allowed widespread use of partially grouted un-tensioned bolts (e.g., passive cable bolts) for primary support; however, pretensioned cable bolts have been accepted.Various solutions using cable bolts as primary support were attempted at two low-seam coal mines in Western Pennsylvania that were experiencing difficult roof conditions. Both mines originally used fully grouted rebar bolts as primary support and cable bolts as supplementary support. It was found that when a large roof fall occurred, the cable bolts may be contained within the dome of fallen rock. As problematic roof conditions continued to exist, both mines decided to use cable bolts as part of the primary support system. The cable bolts were located near the ribs of the entry, to increase the likelihood that they would be anchored outside the dome of potentially unstable roof. The cable and rebar bolts were installed on a heavy steel channel that acts as a ‘sling’ to distribute the load across the width of the entry. At the first mine, Mine A, pre-tensioned cable bolts were used while at Mine B, un-tensioned cables were used. The two support systems consist of essentially the same support components installed in different patterns and with varying degrees of pre-tension."

Jan 1, 2015

By Syd Peng, Gamal Rashed

"Bumps in coal mines have been recognized as a major hazard for many years. These sudden violent failures around mine openings have compromised safety, ventilation and access to mine workings. Previous studies showed that the violence of coal specimen failure depends on both the interface friction and width-to-height (W/H) ratio of a coal specimen. The mode of failure for a uniaxially loaded coal specimen or a coal pillar is a combination of both shear failure along the interface and compressive failure in the coal. Unstable interface failures provide a sudden de-confinement to coal rib, thus triggering uns and compressive failure in the sidewalls. The compressive failure of a coal specimen or a coal pillar can be controlled by changing its W/H ratio. As the W/H ratio increases, the ultimate strength increases. With a proper combination of interface friction and the width-to-height (W/H) ratio of pillar or coal specimen, the mode of failure will change from sudden violent failure, which is brittle failure to non-violent failure, which is ductile failure. The main objective of this paper is to determine at what W/H ratio and interface friction the mode of failure changes from violent to non-violent. In this research, coal specimens of width-to-height ratio ranging from 1 to 10 were uniaxially tested under two interface frictions of 0.10 and 0.25. The results are presented and discussed.INTRODUCTIONCoal mine bumps are sudden, violent bursts of coal from a pillar or pillars or a block of coal, resulting in a section, the whole pillar, or the solid block of coal being thrown into an open entry. These bursts are accompanied by very loud noises (Peng, 2008). Several case histories in mining have long described coal pillars or coal faces failing violently with an accompanying ejection of debris and broken material into the working areas of the mines (Campoli et al., 1987; Osterwald, 1962; Peperakis, 1958; Garvey et al., 2013). Because of the catastrophic nature of these sudden failures, understanding the causes of coal mine bumps is essential to create a safe underground working environment. This phenomenon has motivated many ground control researchers to conduct extensive field investigations throughout the past century. Rashed and Peng (2014) compared the mechanical properties of two kinds of coal, one from bump and the other from non-bump-prone mines. They found that coal itself does not play any significant role in coal bumps and recommended that future research should focus more on the local variation of geological conditions such as the interface friction between pillar and roof and between pillar and floor."

Jan 1, 2015