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By B. Andersen

An accurate knowledge of Interactions among mineral particles and between such particles and dissolved and precipitated species Is Important in developing efficient separation processes. In this investigation interactions in Florida phosphatic clay waste, that are relevant to dispersion and selective reagent adsorption, the two main prerequisites for selective flocculation, were studied. Initial studies with artificial slimes, consisting of pure clay and phosphate minerals, showed dispersion of artificial slimes to be relatively easy. The problems that were encountered during selective flocculation of the artificial slime were due to unselective polyacryllc acid adsorption on clay, which was caused by the presence of multivalent calcium ions on the exchangeable cation positions on the clay surfaces. This problem could be solved by exchanging calcium for sodium, which reduces the interaction between the polymer and the clay surface. This procedure, however, was not successful for mineral mixtures. Natural slimes were found to be much more difficult to disperse. This was attributed to the presence of cementing materials such as humic substances and Ai and Fe (hydr)oxide precipitates. Selective removal of these cementing materials resulted in good dispersion and partial separation. Further increase in separation of natural slime is likely determined by the presence of calcium on the clay surfaces, as was found for the artificial mixtures.

Jan 1, 1992

By Donald D. Murphy

My first contact with underground, bolt conveyors came when I was hired as a draftsman by the La-Del Conveyor & Manufacturing Company in 1935. At that tine relatively few nines were using haulage belt conveyors. Wore they were in use, they were usually loaded by chain or shaker type room conveyors which in turn were hand loaded at the working face. Duo to the low room tonnage, a gathering belt might receive who output of from six to eight rooms. For several years belts 26 and 30" in width were the favorites for coal mine use. Belt speeds very seldom exceeded 200 ft. per mm. at that time. Conveyor lengths for the majority of units lay between 1.000 and 2000 ft. For a number of years 25 H.P. drives were adequate for those conveyors. From 1940 until about 1950 loads and speeds went up slightly and 40 H.P. drives became the standard. Since the majority of mines were then using direct current power systems, we were able to use controllers with 3 or more steps of starting resistance. The slow belt speeds coupled with relatively long starting cycles kept the rate of acceleration low and gave us smooth, easy starts.

Jan 1, 1963

By S. E. Younis

The mining industry is currently looking to better understand, anticipate, and be able to mitigate business and operational risks in order to deliver the rewards of risk taking, and to minimize the frequency and impact of risk on the downside. Assessing risk works from the premise that the identification and management of existing risks can be very challenging, especially when threats are not easy to detect, the likelihood of occurrence is difficult to gauge, and/or the consequences are uncertain. Some approach this as a ?check the box? task, even though fire and safety incidents continue to occur and investigations often find the hazard analyses did not properly identify the cause or consequence. You cannot engineer protective designs and safeguards for causes and consequences that have not been identified appropriately. For the mining industry, risk management is an important tool for making critical decisions and, in some cases, meeting regulatory requirements. Providing high-quality documentation that meets both regulatory and corporate requirements is critical for maintaining safe, uninterrupted mining operations. Risk management is a five-part process: 1. Identify the hazards and their causes, 2. Determine the hazard consequences, 3. Calculate the frequency of occurrence, 4. Quantify the risk associated with the system, process, or procedure, and 5. Provide feasible solutions for the risks

Jan 1, 2012

By J. Pancher

"Stainless steel castings are used in abundance in the mineral processing industry. In rotary kiln-based processes, these castings are typically exposed to high loads, corrosive elements, mechanical abrasion and cyclical temperature exposure. In the processing of iron ore pellets, it is typical to use a traveling grate preheater or a straight grate furnace to heat the pellets. Both machines have a conveyor that is mainly comprised of high temperature stainless steel castings. It is these castings which are the focus of this study. The expected life of these castings can be quite short, their cost quite high and the effort to replace them very labor intensive. The goal of this study was to gain a better understanding of the failure modes of these castings. With that basic understanding, modifications to the alloy content could be made to achieve a new operational paradigm. That paradigm could be a cheaper casting, a longer lasting casting or a casting tailored to special operating conditions (for example, highly corrosive gases or sudden temperature shocks). Over the past 4 years, Metso Minerals has sought to achieve a better understanding of the failure modes through modeling, laboratory testing and sampling of used castings from various end-users. In addition, we have tested new alloys in a laboratory setting and also in the field to see how they would perform compared to the existing ""standard casting"". Our testing has revealed interesting data concerning the impact toughness, sigma phase content and formation, chloride attack and other performance attributes of various grades of stainless steel when exposed to cyclical temperatures. Interesting results were also obtained concerning the addition of rare earth elements (Niobium, Boron, etc), nitrogen and manganese to a typical ASTM A297 grade of stainless steel. To date, a few hundred test castings have been installed in iron ore pellet plants worldwide. Many of these test castings have already experienced a year or more of operation with good results.INTRODUCTION Cast stainless steels (ASTM A297 and similar) are a main constituent used in the construction of iron ore pelletizing equipment. A typical straight grate pelletizing machine would contain upwards of 160,000lbs of ASTM A297 Grade HH castings. With a typical casting lasting only two to four years, and a casting costing around $35USD, it is easy to see that the castings are a main contributor to the overall cost of producing the pellets. Grade HH and HI (see chemical composition listed below) became the “go to” materials in the 1960’s and very few changes have been made to this day (the exception being plants that switched to flux pellet production in the 1980’s)."

Jan 1, 2015

By Bruce H. Mason

The exploration for a commercially acceptable deposit of limestone is consid¬ered by many to be a relatively easy task; however, trying to locate a zone of high calcium limestone of economic thickness within a formation, which outcrops only in a narrow band varying in width from a quarter mile to ten miles, adds considerably to the normal problems experienced during an exploration program. The existence of varying glacial and karst features in the outcrop area intensified the problems encountered and complicated the interpretation of the economic value of the deposit. This paper highlights a recently completed five year exploration program during which approximately 3,900 acres of ground in seven civil townships were evaluated as potential sources of high-calcium limestone. Details are given with respect to the final site chosen and the methods used in determining the suitability of the site. This site exhibited many karat features and several methods were utilized to determine the effect of these features on the gross characteristics of the deposit. Aerial photography for both mapping and interpretation were utilized. Black and white panchromatic photography, black and white infrared and color infrared photography were flown. Resistivity, diamond core drilling and close-interval angering were used to supplement the information obtained from the aerial photography.

Jan 1, 1974

By James J. Anthony

High-angle in-pit conveying is an idea that is being seriously studied by a number of important mining companies in North America. Its application in coal, iron ore, and copper mining is expected to reduce mine operating costs considerably compared with the conventional discontinuous methods, such as truck haulage, which are fuel, labor, and maintenance intensive. Therefore, a mine introducing high-angle in-pit conveyors will gain a competitive advantage over mines which continue to use conventional haulage. While the capital outlay for in-pit conveyor systems obviously varies depending on pit depth, the angle of incline, and the capacity required, it generally will not exceed that of truck haulage when all Factors are taken into consideration. These factors include the cost of excavation, as measured in relation to the volume of minerals mined, the cost of building truck ramps and roads, and the capital outlay for the trucks and maintenance facilities. In many cases, in Fact, the capital outlay will be less than for truck haulage. This cost advantage will best be realized by new mines, whereas in existing producing mines the switch from truck haulage may involve the abandonment of a substantial capital asset.

Jan 1, 1983

By R. M. LaDouceur, C. A. Young, W. Nicholas

"Salicyl hydroxamic acid (SHA) adsorption on two rare earth oxides, lanthanum and yttrium, was studied. Adsorption at both surfaces occurred in two stages. Initially, the monovalent anionic collector appears to adsorb significantly and instantaneously in stage one and then becomes sluggish in stage two presumably because the initial stage passivated the surface. By comparison, adsorption during the sluggish second stage with lanthanum oxide did not stop but with yttrium oxide essentially stopped. Surface monolayer formation could not be observed in either of the two cases. Both stages appear to be due to multilayer formation of a surface precipitate as proven by Raman Spectroscopy for lanthanum oxide but inferred for yttrium oxide. Unlike the use of octyl hydroxamate as stated in the literature, increasing temperatures do not increase adsorption such that flotation of rare earths with SHA may be performed at room temperature leading to improved recoveries as well as significant energy savings. INTRODUCTION Rare Earth Elements (REEs) are comprised of the 15 lanthanides along with scandium and yttrium. The REEs with lower atomic numbers are relatively more abundant and are categorized as light REEs. On the contrary, the REEs with high atomic numbers are less abundant and referred to as heavy REEs. They are not really “rare” and, in fact, some of them are quite abundant in the Earth’s crust; it’s just that they “rarely” exist in concentrated deposits but rather are found dilute and practically everywhere. REEs share very similar physico-chemical properties but, because many of these properties are unique, they have gained enormous importance in recent times making several critical and strategic pending their use. For example, REEs have found extensive application in phosphor coatings, magnetics, and automobile cracking catalysts. Early technology was not advanced enough to produce commodity level production of the REEs and can be attributed to REE-bearing ores containing many rare earth minerals (REMs), not just one. In this regard, there are numerous REMs but bastnaesite, xenotime and monazite are considered to be the most common. Bastnaesite is a fluorocarbonate whereas the other two are phosphates. The separation of the individual REE-bearing minerals from the ores is not an easy task since they also exhibit very similar properties. Consequently, when flotation is used, it is done to produce bulk REM concentrates. For REM flotation, it is well established that octyl hydroxamate is more selective than fatty acid collectors (Pradip and Fuerstenau, 1983 and 1991). Liu et al. (2006) indicated that hydroxamates are the most common collectors for REMs. Pavez et al. (1996) studied the adsorption of oleic fatty acid and octyl hydroxamate on REM surfaces. Cui et al. (2012) studied the interaction of octyl hydroxamate with various REMs surfaces using various spectroscopic techniques such as XPS, FT-IR and Raman along with electron microscopy and concluded that such techniques offer ample information to establish adsorption mechanisms. Ren et al. (1997) studied napthalenic hydroxamic acid as a unique collector for flotation of REMs from bastnaesite ore and indicated that more selective collectors were needed. From these studies, it is clear that the quest of more selective collectors is essential but understanding how they adsorb at mineral surfaces is prerequisite to improving flotation performance."

Jan 1, 2016

By Kenneth W. Luke

In the development of the ultimate pit limits for a narrow ore body, pa¬rameters necessary in the design of a functional, or working, pit become highly sensitive factors in the determination of ore reserve levels and their associated waste to ore stripping ratios. Through the use of geologic cross sections, ore reserves can be roughly calculated by utilizing a straight line approximation for pit wall slopes. The optimum position of the pit floor can be substantially altered from such a preliminary design though with the introduction of functional mining parameters, such as a ramping network, and working bench heights, berm widths, and bench to bench wall angles. Originally a computer program was developed to quickly evaluate changes in cross-section pit design with minimal alteration of input data. After developing a satisfactory technique of cross-section evaluation which incorporates working mine parameters, an optimization algorithm, or procedure, was developed and included in the program to eliminate much of the tedious manual decision-making required in determining the optimum location of the pit floor on each cross section. Optimization in this case implies the maximum profit pit. When pit and processing costs are defined or hypothesized, this computer program can be used to design the maximum profit pit, constrained by the recognized functional mining parameters. A second way of stating the optimization is that the program can be used to develop a pit design which minimizes waste stripping at any desired ore reserve level. The basic method of cross-section evaluation parallels present manual methods. Program input is a combination of data obtained directly from cross sections developed for, geological interpretation and pit design parameters selected by the mine planner. As a result it is easy for the mine planner to comprehend what the program is accomplishing, and thus participate in the development of the computer assisted design.

Jan 1, 1971

By Joseph Githiria, Khadija Omar Said

Mineable material is defined using cut-off grade either as geological or economic cut-off grade. Both geological and economic cut-off grade affects the output generated in an open-pit mining operation. It distinguishes the amount of ore sent to the mill for processing and waste to the dump. This consequently affects the overall profits generated from the operation hence the need for cut-off grade optimization. There are several mining parameters that are considered in a typical cut-off grade model. They include economic, geological, and operational parameters. They have a significant effect to influence the cut-off grade selected in mining operations at any given period. Some of the parameters are stochastic in nature by having a random probability distribution that may not be predicted precisely. When selecting cut-off grades in a mine operation, the mining engineers must consider the dynamic nature of the operational parameters in order to maximize the net present value of the project. Modifying Lane’s cut-off grade model which was developed in 1964 to incorporate the stochastic parameters in the approach helps improve the net present value as shown in the paper. The modified Lane’s approach is developed into a stochastic computer-aided application code-named NPVMining. Using NPVMining, selected stochastic parameters are considered in this exercise to show the effect on the output (net present value). The selected parameters (price and grade-tonnage) are varied by ± 10%. NPVMining has a graphical user interface that makes it easy to use and displays results in a user-friendly way. It gives the user the choice to manipulate the data depending on the study being undertaken or any other factor affecting the specific mine. This paper analyses the effect of each of the selected mining parameters on cut-off grade using NPVMining to show the significance of monitoring their variance.

Jun 25, 2023

By J. E. Brownhill

This paper does not deal with the typical start-up issues of equipment, production capacity or work force. This is a description of the challenges faced and the changes made by the project team to bring to fruition the reconstruction of Port Inland. Many honored traditions and norms had to be overturned to find the winning combination that provided the productivity, flexibility and cost necessary to survive in today's competitive minerals environment. This paper covers the innovation in terms of machinery, operations, and management philosophy that permitted the renovation and reopening of Port Inland as a commercial limestone producer in the spring of 1992. Port Inland, constructed by Inland Steel in 1930, operated as a captive source of metallurgical grade limestone for the steel industry until its closure in 1989. Located in the Upper Peninsula of Michigan on the north edge of Lake Michigan, the operations consist of a deep water port facility with crushing, screening and stockpile storage for 500,000 tons of finished product at the port. Ninety-nine percent of the stone is shipped via lake boat to ports within the Great Lakes. The operation is unique in that both metallurgical Dolomite and Limestone are produced on site. In 1930, Port Inland was at the fore front of technological advancement. It was the first major mining operation to use roller bearings and other equipment innovations. Over the 60 years of operation, Inland Steel placed emphasis on steel making technology and iron ore mining at the detriment of the limestone operation. By the early 80's, Port Inland was no longer a leading competitor. Inland Steel, unable or unwilling to spend the capital to modernize, closed the facility in the fall of 1989.

Jan 1, 1994

By Keh-Jian Shou

"This study adopts and analyzed a shield tunneling case in Taiwan, with a diameter from 5.25m to 6.70m and the smallest radius of curvature 100m, which was constructed in gravel formations as well as a vibration sensitive area. In this case study, a vibration monitoring plan, comprising the sensors inside the shield machine and on the surface, was proposed and performed to provide the vibration data during the construction. In this project, the major vibration reduction considerations were increasing the open ratio of the cutter head (to reduce the cutting function) and reducing the rotational speed of the cutter head. The results of the construction suggest the appropriateness of the above considerations. The findings could provide suggestions to the other similar shield tunneling cases. INTRODUCTION Underground vibrations during shield tunneling are typically isolated and absorbed by the soil. However, a portion of these vibrations may disseminate to the surface. These vibrations are considered micro-vibrations, which generally do not pose a threat to surface structures, and are thus seldom the focus of research. The present project was located in the Hsinchu Science Park where shield excavation bypassed numerous high technology manufacturing plants (e.g., wafer manufacturing plants). The vibrations generated by shield tunneling may affect the vibration-sensitive manufacturing equipment and instruments in these plants, and induce problems in manufacturing processes. Therefore, research to comprehensively understand the characteristics and potential influence of such vibrations is essential. To clarify the characteristics and potential influences of vibrations generated during shield tunneling, the vibration level in the excavation of the Taoyuan International Airport Access (TIAA) Metropolitan Rapid Transit (MRT) Project was examined, as it possesses similar excavation conditions to the present project. The parameters collected from relevant tests were provided as a reference to the firms along the excavation route of the present project to explain the effects of vibrations, and to relevant units for shield machine selection and project execution. No yield problems resulting from shield machine induced vibrations were reported by the firms, and the vibration levels measured in the present project were comparatively lower than those in the TIAA MRT Project. Because the related literature is scarce, this study aims to analyze the collected measurement data and provide suggestions on shield machine selection or designs. Such that we can more properly evaluate and control the impact of shield tunneling induced vibrations in similar projects."

Jan 1, 2016

By T. A. Toney

A sampling program was conducted in 2008 to determine the run of mine characteristics of 5 coal seams. The sampling program included size analyses and float sink determinations. The samples were analyzed for ash and mercury concentrations for each size and gravity fraction. This paper will report on the sampling program, the analytical results, and the correlations determined in the data set investigated.

Jan 1, 2010

By B. J. Sauer

Misapplication of AC induction motors for mine crusher and mill applications has long been a frustration for both the driven equipment supplier and the mine operator. Proper selection of AC induction motors is critical to providing efficient production. This paper focuses on the selection of AC induction motors for gyratory crusher, cone crusher, and grinding mill applications. The criteria for motor selection includes: proper enclosure, driven equipment torque requirements, bearing life, temperature rise, starting requirements, ambient temperature, altitude and accessory requirements.

Jan 1, 1999

By H. EI-shall

In this paper, the results of a fundamental study involving zeta potential and turbidity determinations of solid suspensions are discussed. Illustrations of how these results are utilized to design field applications of solid grade polymers to clarify mine drainage water are presented. Other applications in different industries are also reported. The operational and economical advantages are examined.

Jan 1, 1994

By R. E. Cook

"Mineral deposits require substantial amounts of energy to transport and be processed into useable form, and as such present a real processing challenge in that the deposits are never homogeneous and ore body compositional characteristics are all over the map! Extracting the desired mineral(s) from the deposit at sufficient profit margin, despite severe fluctuations in market price, requires process automation architecture capable of supporting an integrated enterprise solution. Such an architecture will encompasses the activities of individuals, process units, process areas, plant level activities, mine management and business planning and accounting systems. Key to the automation process is the aspect of value generation. This paper brings together the various requirements for the automation of a mining enterprise and presents the different aspects of how to obtain value across the entire mining operation.INTRODUCTIONMinerals’ processing sites are historically long lived, 20 year life of mine is not uncommon and 75 years is not unheard of. Considering that hardware technology advancements are introduced every six months, or less, it is prudent to select process automation systems that adhere to “open” industrial standards versus proprietary based systems. In the minerals processing industry, the key to survival is driving the cost of production per unit volume to the lowest possible level and provide enough profit to sustain operations. Control system architecture and Business information technology are rapidly becoming important tools in the quest for productivity. Getting key dynamic business performance information at the right time to the right person or process unit is crucial to successfully achieving corporate goals. The process automation architecture selected must therefore be able to integrate to the various networking enterprises and business systems.The mining industry is generally known as an “extractive” industry that is very physically-oriented with respect to operations and the activities in which workers engage. Large numbers of people performing manual tasks in difficult surroundings, produce very variable outputs. But, times are changing – and so are industry best practices. While the nature of work still consists of activities such as ore extraction, ore movement, ore concentration, refinement and logistics, automation innovations are starting to change the nature of many of the production steps. The industry has transitioned from requiring more physical activities by workers, to more information management, automated control and collaboration within the operation. Humans are good at situational intervention and non-linear reasoning and do best when empowered with an overall production perspective. Machines and automation are good at repetitive functions, steady state operation, and managing transitions. Thus, a combination of advanced technology solutions, reliable and useful information and full human contribution are necessary to mining operations for value generation."

Jan 1, 2015

By Harvey Parker

"The International Tunnelling and Underground Space Association (ITA) is a nonprofit organization that represents all aspects of the tunneling and underground space industry worldwide. Next year, the ITA will be holding its annual World Tunnel Congress (WTC) in San Francisco, CA, April 22-28, 2016. The ITA’s mission is to be the leading international organization advancing the entire industry and promoting the use of tunnels and underground space through knowledge-sharing and application of technology. This article updates a series of articles about the ITA prepared in 2007 by Harvey Parker, former president of the ITA, in anticipation of the next WTC in San Francisco.ITA accomplishes its goals through a range of activities that includes organizing conferences, workshops and meetings, working group and committee studies, training, experiments and other activities. ITA is also involved in the publication of proceedings, reports, and guideline documents as well as facilitating interaction among its membership and with sister organizations and decision makers. ITA currently includes 73 member nations and several hundred affiliate members, including 15 prime sponsors and 63 supporters. ITA’s membership is comprised of member nations as well as sponsors and affiliate members.The United States has had a prominent role in ITA since its 1974 inception, when it was formed as a result of a worldwide survey conducted in the early 1970s by the Organization for Economic Cooperation and Development (OECD). Bill Lucke, from the U.S., who was in charge of tunnels for the U.S. Federal Railroad Administration, was a member of the organizing committee that created ITA and became a vice president of ITA. Jack Lemley served as president of ITA from 1983 to 1986. Dick Robbins was active in ITA and served for many years as a member of the ITA’s Executive Council and as first vice president. Harvey Parker served as president of ITA from 2004 to 2007. Amanda"

Jan 1, 2015

By Neil B. Prenn

Mine Development Associates, Inc. was formed in March of 1987 to provide mine engineering assistance to the mineral industry. To be competitive with other firms, Mine Development must be able to provide quick and accurate ore reserves and mine plans for clients. Commercially available mining software was necessary for Mine Development to assist the client. This paper describes how Mine Development chose mining software, the time involved in getting up to speed, and several case histories of how the software is used. The case histories discussed include: * 3,000,000 ton gold deposit in Nevada. * 5,000,000 ton gold deposit in South Dakota. * 1,000,000 ton gold deposit in Australia. * +100,000,000 ton gold deposit in Nevada. * 25,000,000 ton carbonate deposit in California.

Jan 1, 1989

By Verya Nasri, James Sullivan, Alex Varas

"INTRODUCTION Many major cities in the United States have a combined storm water and sanitary sewer network. Regular rainfall overwhelms the system capacity and results in millions of cubic meters of untreated sewage being dumped into local waterways. One legally mandated solution includes several kilometers of large diameter shallow or deep rock or soil tunnels, a pump station as well as associated collection sewers, diversion structures and drop shafts. In this paper, the basis for design of different system elements including the drop shafts and pump station is explained in detail. Common construction methods used for different type of shafts including tangential vortex and baffle plunge, and also pump station alternatives comprising cavern or various shaft configurations are discussed. DIFFERENT TYPES OF PUMP STATIONS The dewatering pump station serves as the heart of any deep CSO tunnel system and is critical to the goal of reducing CSOs by providing a controlled release of the stored tunnel volume to the wastewater treatment plant. As the major mechanical component of the project, the station will require the greatest attention by operations and maintenance staff. Designing a durable and easily operated pump station requires addressing some major challenges, including the following: • Longevity – equipment, materials of construction, and station environment • Controlling odors • Safety for operators and maintenance personnel • Easy access to equipment • Protection from hydraulic surges Location. Owners face a fundamental decision relative to the location of the pump station, which will affect how these challenges are addressed. The pump station can be built within the tunnel launch shaft or within its own dedicated shaft. This decision is driven by cost and schedule. Use of the tunnel launch shaft may provide owners cost saving opportunities by not having to construct a separate pump station shaft. However, this will likely extend the pump station construction as much as two years until the tunneling has been completed. Furthermore, delays to the tunneling operation would delay the pump station construction work, potentially leading to delay claims. For this reason, it has been more common to utilize a separate pump station shaft on recent CSO tunnel projects (Nasri et al. 2015)."

Jan 1, 2016

By A. B. Cecala

Enclosed cabs have been used on surface mining equipment for many years to protect equipment operators from health and safety hazards. The surface mining and quarrying process is a highly mechanized process that generates large quantities of respirable dust. Due to economic factors, more older mining equipment is being used today than in years past. With this older equipment, it is common to observe deterioration of many components on the enclosed cabs which greatly reduce their protection effectiveness. NIOSH has performed a number of different field studies, as well as a comprehensive laboratory study evaluating various factors and parameters regarding enclosed cabs. NIOSH has recently completed a cooperative research effort with Sy-Klone International and Vulcan Materials Company to evaluate the effectiveness of a newly designed uni-directional filtration and pressurization system that brings all the clean filtered air in at the roof of the cab and extracts all recirculated air near the floor. This design provides the highest air quality to the equipment operator. Testing on this new system showed an almost 10-fold reduction in respirable dust inside the enclosed cab. The uni-directional design is easy to incorporate and should be considered for all new and retrofit systems in surface mining equipment.

Jan 1, 2009

By Reece Kurre, Gabriel Walton

"Roof bolting has long been used in underground mines across the world to provide ground support. Modern roof bolts are cheap and easy to install with the use of specialized machines as a part of the production cycle. Lhoist North America’s Crab Orchard Mine is an underground room and pillar limestone mine that uses mechanically anchored roof bolts for ground support. The mine currently employs two different roof bolting patterns: a standard 5 × 5 foot pattern, and a 2.5 × 2.5 foot pattern for use in areas with particularly hazardous roof conditions. The purpose of this study is to evaluate the relative effectiveness of each bolting pattern.A series of numerical models were created using RocScience’s RS2. The models were based on a symmetrical section of the mine at its deepest point, and were modeled using Generalized Hoek-Brown failure criterion along with a discrete fracture network. A series of sensitivity analyses were performed on the models by varying parameters such as joint friction angle, crack persistence, joint randomization, and tensile strength of the limestone. Based on the results of the original models and sensitivity analyses, it appears that the standard bolting pattern provides sufficient roof support capacity under almost all the expected conditions at the mine, since factors of safety below the design value of 1.5 were only found for individual bolts in a few of the worst test cases considered. These results can help improve the Mine’s productivity and reduce operating costs without compromising safety.INTRODUCTION AND CASE STUDY DESCRIPTIONLhoist North America’s Crab Orchard Mine is an underground limestone mine located in Crab Orchard, Tennessee. The mine is located under an 800-foot-high mountain, and outcrops on three sides. The mine is accessed through three separate portals and has two main levels, along with a partially developed third level. Extraction is accomplished by the room and pillar method using 50 × 50 feet pillars and 50 × 50 feet rooms. The mining height is limited to 50 feet to keep the pillar width to height ratio around 1.0. Each heading is excavated in a two-stage process that consists of a 30-foot-tall top heading and a 20-foot-tall bench. A distance of at least 30 feet is maintained between the two levels at all times (Crab Orchard Mine Technical Staff, 2017)."

Jan 1, 2019