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By H. J. Chen

In recent years, it has been recognized that the high horizontal stress is an important factor that contributes to a cutter roof. When the immediate roof is thinly bedded, the presence of a high horizontal stress may first cause failure on the bedding planes or weak planes, and then a cutter roof develops as the individual stratum crushes and buckles progressively layer by layer. In this study, the stress distributions in the bedding planes of the immediate roof are analyzed for an entry-pillar system in the multiple longwall panels by using the finite element method. Then the roof failure is analyzed based on the rock failure criterion and the stress distributions.

Jan 1, 1998

By Ronald A. Crowson

Detailed stratigraphic studies of the overburden at North Carolina Phosphate Corporation new South Creek Mine have delineated several aquifers and acquicludes within the 30-meter-thick overburden section of late Pleistocene sands and clayey sands. A major aquifer occurs in the 10-meter-thick sequence of shelly sands of the early Pleistocene Croatan Formation. The water-charged Croatan sands thicken into a paleodrainage surface on top of the Pliocene Yorktown Formation, a major aquiclude. A three-phase dewatering program is projected: 1) improve surface drainage around mine perimeter to reduce both flowage into the pit and rainfall recharge; 2) use a wellpoint system to dewater the upper 8 meters; and 3) use recharge wells along the axis of the paleo- drainage to dewater the overburden below 8 meters.

Jan 1, 1983

By Gordon B. French

In order to better understand the relation- ship of underground and surface oil shale processing systems, a block flow chart is presented in Fig. I. From this figure only modified in-situ and Room and Pillar underground mining are currently committed and into the Detailed Design and Construction phases. Figure II illustrates the times required (Federal land site) to bring oil shale operation into production. As this example shows, only those companies having progressed beyond the exploration stage have a chance to obtain oil shale production within the next 10 years. A more detailed breakdown of the oil shale development for those on private lands or having already obtained Federal lease lands is shown in Fig. III for shale oil development (without major regulatory changes).

Jan 1, 1981

By C. Treworgy, C. Chenoworth

Geologic and technical factors such as coal seam thickness, stripping ratios, roof conditions, partings, faults, and size and geometry of the reserve block greatly impact the availability of Illinois coal for mining. Residential and commercial developments also restrict access to coal reserves in some areas. Despite the collective effects of these factors, large blocks of bituminous coal reserves suitable for efficient, low-cost underground mining remain available in Illinois.

Feb 24, 1997

By Caroline Gerwig, Joseph R. Wickline, Zach Agioutantis

In longwall mining, the progressive caving of the roof allows stored energy to dissipate over an extended time. However, in some cases, the roof strata above the longwall panel are unusually strong and do not break with the movement of the working face. Instead, the roof material bridges over the expanse of the longwall, forming an unstable beam. Later, when this beam breaks, the stored energy can release suddenly, causing a seismic event to propagate to surrounding mine workings. The focus of this paper is to estimate the size of beams that form over longwall panels to the seismic energy recorded by the mine. Analytical calculations are used to verify two-dimensional models of longwall roof beams to determine the strain energy and gravitational energy developed, which is then released upon strata failure to surrounding mine workings. Models are developed using RS2 to model the stress, strain, and deflection along the bottom of the longwall roof beam to calculate gravitational and strain energies. Gravitational energy is shown to be the main driving factor in energy release, except for the beams with low heights. Analyses allow the determination of beam characteristics based on seismic data. The analysis is refined using swelling factor to compare various beam drop heights. The models show an increase in seismic magnitude for higher drop heights. However, the actual data provided by the Buchanan mine displays a decrease in seismic magnitude with increasing drop height, indicating that energy is dissipated into the broken gob material as drop height increases.

Jul 1, 2023

By John J. Dwyer

As one begins to contemplate the organization of a talk with the title "Iron Ore - The Permanent State of Evolution," the main divisions appear to be the past, the present, and the future. But distaste for repetition of the present production achievements, which scarcely need additional description on this occasion, soon leads one to the conclusion that a more appropriate division of the subject is simply the past and the future . . . with emphasis on the future. We are working in the present, but it can only be understood by what has taken place in the years and decades gone by, and/or under what terms we will have to face the future. Evolution is more often thought of as a steady change - but steady change is really the product of revolutions, sometimes making headlines but often unnoticed at the time. With hindsight, we recognize the great importance of the emergence of the Bessemer converter and the open hearth and the vast influence that both have had on steel making and the changing ore demand. In this country we also see schooners opening the era for lake transportation of iron ore from Michigan to Take Erie. Later, steamships haul the ore from the Mesabi Range to the steel centers of the country. In order to take full advantage of the inland seaway, there had to be revolutions in ship design, loading and unloading facilities and channel and lock development. Full scale utilization of the resources of the Mesabi Range, itself, required parallel upheavals such as the development of new production equipment, and substitution of modern forms of energy for horsepower, and, yes, manpower, as well.

Jan 1, 1968

By P. C. Kapur

For mineral processing spirals, mathematical force equilibrium models are sought to extend the spiral performance envelop. In Part 1 of this report, a complete geometric description of the helical spiral and its trough or channel contour is provided. The secondary circulatory fluid motion in the transverse direction that develops when water flows down a tightly turning curvilinear path and its implications for gravity separation are discussed. Different forces that act on the particle during its passage through the spiral are enumerated and quantified for a better appreciation of their relative contributions and roles in the separation process. Three force equilibrium models from the hydrology literature on sed iment transport are employed to simulate a typical spiral. While the results are promising in that the models mimic the broad performance characteristics of the spiral, what is needed is a more general spiral model taking explicit cognizance of the missing components essential to the spiral description. These are such components as centrifugal force and the steep tangential slope of the channel deck. Results of this latter exercise are deferred to Part 2.

Jan 1, 1996

By M. Superfesky, P. Michael

Introduction The US Office of Surface Mining (OSM) is proposing changes to the Code of Federal Regulations in the interest of minimizing the adverse effects of excess-spoil-fill construction on the “prevailing hydrologic balance, fish, wildlife and other environmental values” (70 FR 35112). The proposed changes will require: (1) minimization the amount of excess spoil generated at a mine site; (2) minimization of the size of the fills constructed; (3) consideration of alternative configurations for disposal; and (4) development of a disposal plan that would minimize adverse impacts to the environment.1 To achieve those objectives, mining companies operating in steep-sloped Appalachia will likely build excess spoil fills (also called valley fills) that toe out at higher elevations in the hollows (i.e. to prevent or limit burial of streams). Consequently, the slopes of fill foundations will generally be steeper. Whereas the authors of this paper support these measures to protect the hydrologic balance and general environment, we wish to point out that placement of fills on steeper foundations can negatively impact the stability of the fills if proper care is not taken during their construction. It is important to note that in addition to impairing human safety, valley fill instability can negatively impact streams, the riparian habitat etc., and thus defeat the very purpose of the spoil minimization measures proposed. We do not, however, propose additional regulatory requirements pertaining to valley fill stability. Rather, we intend to emphasize the importance of engineering requirements already on the books, especially as they apply to the predominant type of valley fill constructed: the durable rock fill. We believe that the practice of restricting valley fills, to higher elevations in the watershed leaves less room for error in the design and construction of stable structures. This paper gives a quick review of the nature of excess spoil generation; methods and requirements of excess spoil fill construction, and the to-date stability record of the fills. The interest in excess spoil minimization and how it affects valley fill construction is also discussed. Most importantly, we will review long-standing issues pertaining to proper design and construction measures with respect to durable rock fills and discuss how they will become more critical as spoil minimization is practiced.

Jan 1, 2007

By J. L. Ellenberger, T. Miller

"A limestone mine in Ohio has had roof instability problems that have led to massive roof falls extending to the surface. This paper describes a collaborative study of these events undertaken by the National Institute for Occupational Safety and Health and the mine owners. The study focuses on the roles that weak, moisture-sensitive floor and weak bands in pillars play in a general instability that led to roof falls at this mine. The NIOSH Stone Mine Pillar Design software (S-Pillar) does not include analysis for weak floor or weak bands and recommends that when such issues arise they should be investigated further using a more advanced analysis. It is important to recognize that without the impact of the floor or weak bands, the calculated inherent stability factor for these pillars is within the recommended design range. Therefore, to further investigate the observed instability occurring on a large scale at the Ohio mine, FLAC3D numerical models were employed to help determine the failure mechanism. Roof-to-floor extensometers were also installed in the areas predicted to have further instability. This case study will provide important information to limestone mine operators regarding the impact of weak floor causing the potential for roof collapse, pillar failure, and subsequent subsidence of the ground surface. This recent case demonstrates that weak floor can be a significant factor in pillar stability and should be assessed during the design stage of the mine.To an area-wide failure (Zipf, 2001). In that case, it appears that the pillars had actually remained intact. However, moisture-related yield of the weak floor caused deformations which passed through pillars and into the roof, triggering roof collapse around the intact pillars (Esterhuizen et al., 2011). This previous case and the case presented in this study, while not identical, both demonstrate that weak floor and/or bands within pillars can be a significant factor leading to instability."

Jan 1, 2015

Caterpillar’s 797 327-t (360-st) mining truck is currently being tested at the company’s proving facilities. Mine evaluations began in the second quarter. The unit will be commerically available in North America in 2000 and worldwide in 2001. The new model is the largest of Caterpillar’s off high-way truck line. In addition, the company has replaced its 966F series II and 970 F wheel loaders with the966G and 972G models. 797 mining haul truck Caterpillar developed the 797 mining haul truck in response to mining companies seeking to reduce cost per ton in large-scale operations. The 797 is sized to work with loading shovels used in large mining operations. And Caterpillar will match the body design to the material being hauled, to optimize pay-loads.

Jan 1, 1999

By E Mutaz, M Bahaaddini, D J. Williams, M Serati

The contribution of the mining industry to the global economy has reached (and gone beyond) $1,800 billion in recent years that necessitates (more than before) the need to ensure workability, viability, health, and safety of mine sites and workers to meet the ever-increasing global demand for mineral resources. Amongst the many challenges facing the excavation industries, rockburst and spalling failures in deep mines in hard and brittle rock formations are yet happening that are still deemed as unsolved problems. During unconfined compressive testing of brittle rocks, microcracks initiate at approximately 0.3–0.5 of the peak strength (which is commonly known as the Crack Initiation stress level) mainly in the direction of the major principal stress, then grow unstably and coalesce to form macro fractures at approximately 0.7–0.8 of the peak load at a so-called Crack Damage stress threshold. From a stress-strain perspective, the crack damage stress threshold () is associated with the reversal point of the volumetric strain, which is also proved to be strongly affected by the intermediate principal stress. This paper extends the previous studies on the impact of true triaxial loading conditions on the CD stress level in high porosity rocks, and introduce a new Crack Mode-Changing Stress (CMCS) defined as the minimum principal stress required to change rock fracturing from splitting to a sliding failure mode. A large number of experiments on sandstone specimens were carried out at different true triaxial loading conditions and the effect of principal stresses on the CI and CD as well as CMCS were studied. The results show that not only the intermediate principal stress, but also the minor principal stress can significantly affect the CD and CMCS thresholds.

Apr 26, 2022

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

By R. O. Burt

The paper examines the role of gravity concentration in both an historical contest and within the modern mineral processing industry. It discusses the principles of the process on both a theoretical and practical level. The importance of ore mineralogy and its effect on the choice of the wide range of equipment available is discussed. The paper concludes with a discussion on the relative merits of gravity concentration to other forms of processing and seeks to answer the classical question - "Quo Vadis?"

Jan 1, 1982

By J. C. Stankus, R. Ochsner, B. Hanson

"Bull Mountains No. 1 mine of Signal Peak Energy made another success in its 4 Right pre-developed recovery entry on March 23 and 24, 2015, after the first successful cut-through and shield retrieval of 3 Right pre-developed longwall recovery entry in 2014[1]. Under the same geological conditions, the major difference of 4 Right and 3 Right is the 600 psi Unconfined Compressive Strength (UCS) value of light-weight concrete in 4 Right versus 800 psi in 3 Right. In addition, one more recovery chute was added in 4 Right. The unique geological conditions in this mine include: (1) the low overburden of approximately 200-260 ft, (2) prevalence of roof joints parallel to the face in the sandstone/siltstone dominated overburden, (3) proximity of the Rehder rider seam to the bench Mammoth coal seam, and (4) prompt surface subsidence with the face advancement. The 4 Right recovery entry was 42 ft wide and developed in two stages, 20 ft wide in the inby Phase I, and 22 ft wide in the outby Phase II. The entry roof was reinforced with steel wire mesh/non-metallic recovery mesh, primary bolts, and high-capacity supplemental SUMO cables. After all the support was installed, the entry was completely backfilled with specially designed, cuttable, low-density cement. It took approximately half time to easily cut through the concrete with less dust in 4 Right as compared to the concrete-cut-through time in the 3 Right. The updated study further explored the nature and mechanism of effective roof control approaches in the pre-developed recovery entry of this unique geology mine, aiming at providing the safest working environment for protecting the miners. GEOLOGICAL AND MINING CONDITIONS OF THE RECOVERY ENTRIES Bull Mountains No. 1 mine is located 30 miles north of Billings, Montana, and currently mines bituminous coal from the Mammoth coal seam. The mine employed a conventional recovery face in Panel #1 and pre-developed recovery entries in Panels #2, #3, and #4 (Figure 1). The typical mining and geological conditions are as follows:Overburden Depth The overburden above the Mammoth coal seam in the #1-#4 Right recovery areas is approximately 200-260 ft. This low cover, in combination with specific roof geological features (especially the prevalent roof joints and proximity of rider seam), constitute unique ground movement characteristics when the longwall face advances into the recovery entry if no sufficient roof support is installed."

Jan 1, 2016

By Y. K. Yen, J. D. Miller, C. L. Lin

The image-based On-line Particle Size Analyzer (OPSA)system has been developed at the University of Utah to measure particle size distributions under plant conditions where overlapped and segregated particles are being transported on a moving belt conveyor. Evaluation of the OPSA system at several plant sites has been completed. The results show a consistent agreement between the particle size distributions obtained from the OPSA system and those obtained from laboratory screen analysis of belt samples. These results and the stable performance of the OPSA system during the field tests suggest that continuous quality control of crushed products is possible using the OPSA system.

Jan 1, 1999

By Poltak Sinaga

PT Kaltim Prima Coal?s 13.1 km overland conveyor (OLC) was commissioned in 1991. It is of conventional 3 roller 350 trough belt type. Cost and performance optimization during initial design ended up with 5.4 mps belt speed, 1000 mm belt width to convey 1350tph, and 7 mtpa of coal. Despite high initial figure, the belt speed was lifted to 6.5 mps in 1996 to accommodate mine throughput increase. In 2002, new low loss ST2100 1100mm wide belt replaced the old ST2250 due for change-out. An upgrade project was initiated at the end of 2003 to further increase the belt speed to 8.5 mps, hence to increase the OLC capacity to 30 mtpa (million ton per annum). Performance data, experience of site personnel, site observation and tests, benchmarking, and information from equipment manufacturers were major inputs to the design review. The project fast track was another challenge in addition to executing modifications on a production lifeline. The project was completed within fifteen months and the OLC was successfully commissioned at 8.5 mps belt speed in February 2005. The OLC has been to date conveying 4 200 tph satisfactorily.

Jan 1, 2008

By Rob Thomas

It is generally agreed that standing support should be installed in roadways that will for various reasons, be holed through with a longwall. Considering the magnitude of the associated abutment loading in conjunction with the need to ensure that the material used is cuttable, some form of cementitious support is often used.

By Peng Gao

Coal-based reduction followed by magnetic separation is an innovative technology used in processing refractory iron ores. Given that size is essential to the separation of the metallic iron from the gangue, the morphology of metallic iron particles and their evolution during coal-based reduction are investigated in the present work. The size of the metallic iron particle increased from 128.76 µm to 565.70 µm when the reduction time increased from 20 min to 60 min at 1,225° C and C/O (i.e., the amount of coal addition in terms of the gram-atomic ratio of the fixed carbon in the coal added to the combined oxygen in iron oxides) of 2.5. Based on our microstructural and metallographic analysis, the iron ore reduction process can be divided into three stages: (1) metallic iron particle formation, (2) iron oxide reduction and metallic iron assembly and (3) metallic iron particle growth. Almost all iron oxides are reduced to metallic iron in the second stage. These newborn metallic iron particles are energetically active and able to assemble and grow, and are eventually separated from the gangue. The large metallic iron particles benefit the subsequent magnetic separation process.

By D. Rucker

Flow models are used to predict the extraction efficiency of metals in rock piles. These models typically use hydraulic parameters obtained through column studies, which assume that the material in the column wholly represents the entire pile and the parameters can be upscaled several orders of magnitude for model evaluation. This assumption fails for parameters that are spatially variable or scale dependent. To overcome these issues, measurements made directly on the heap at the appropriate model scale can be made with the electrical resistivity method. The method aims to map the variations in the electrical resistivity, which can be associated with moisture content, degree of fines, metal content, and leachate concentration. We present an example of calibrating the resistivity with borehole measurements of moisture using geostatistics to show how the resistivity method can be used to obtain a spatial moisture distribution. It was shown that cokriging the resistivity and moisture together gives a more reliable distribution.

Jan 1, 2010

By Nathan Bowersox, Zuzana Skovajsova, David M. Jurich, Brian Harris

When unwatered after more than 50 years of operation, the White Rock Tunnel of the Upper American River Project in the foothills of the Sierra Mountains exhibited failing rockbolts and ground falls. Repairs designed for the 5 mile-long, 24-foot horseshoe unlined hydropower tunnel included pattern rock bolts, shotcrete, and cleanout of the rock trap. The work, originally scheduled for two 3-month winter outages, was completed under challenging conditions in a single 4-month outage following a carefully sequenced work plan using robotic shotcrete and rockbolter machines. Flexibility, creative solutions, and collaboration by all parties were key to project success.

Jun 13, 2021