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By M. L. Harris, J. Organiscak, S. Klima, I. E. Perera

"The Pittsburgh Mining Research Division of the U.S. National Institute for Occupational Safety and Health (NIOSH) conducted underground evaluations in an attempt to quantify respirable rock dust generation when using untreated rock dust and rock dust treated with an anticaking additive. Using personal dust monitors, these evaluations measured respirable rock dust levels arising from a flinger-type application of rock dust on rib and roof surfaces. Rock dust with a majority of the respirable component removed was also applied in NIOSH’s Bruceton Experimental Mine using a bantam duster. The respirable dust measurements obtained downwind from both of these tests are presented and discussed. This testing did not measure miners’ exposure to respirable coal mine dust under acceptable mining practices, but indicates the need for effective continuous administrative controls to be exercised when rock dusting to minimize the measured amount of rock dust in the sampling device IntroductionTwo recent regulations have modified operators’ rock dusting schedules in order to meet compliance standards. First, the 80 percent incombustible requirement in intake entries has increased both on-section and out by the- section rock dusting. Secondly, the recent change to the respirable dust regulation has increased the number of respirable dust samples taken per sampling cycle. Previously, when only five samples were needed bimonthly, rock dusting could be scheduled to not interfere with the respirable dust sampling schedule.The significant number of samples now required under new regulations, combined with the need to maintain 80 percent total incombustible content in active mining areas, require the schedules for respirable dust sampling and rock dusting to overlap. Although rock dust is considered a nuisance dust in relation to U.S. Mine Safety and Health Administration (MSHA) sampling, these overlapping schedules raise concerns about the amount of rock dust that potentially is included in the sample. Additionally, the respirable dust maximum was lowered from 2.0 mg/m3 to 1.5 mg/m3 effective Aug. 1, 2016, increasing concern that rock dust contamination may be an issue (MSHA, 2016). Currently, the acceptable practice is to apply administrative controls such as keeping the miners upwind during rock dust application, or to schedule rock dusting during a maintenance shift when the number of miners present is lower."

Jan 5, 2017

By N. Myung, G. Hwang, H. Kim, Y. Han, S. Choi

"According to research presently being conducted on selective lithium recovery in seawater, inorganic adsorbents with high selectivity and capacity for capturing lithium ions from liquid lithium resources are called lithium ion-sieves (LISs). Their low toxicity, low cost and high chemical stability make LISs suitable for lithium recovery from seawater. In the present study, the ultrathin LMO nanofibers with controlled diameter were successfully fabricated by an electrospinning technique with a hypothesis that greater aspect ratio (i.e., smaller diameter) would lead to the enhanced recovery of lithium ion from seawater. Design of Experiment (DOE) and dimensionless analysis were performed to systematically optimize the diameter and morphology of nanofibers. Several complementary techniques including FE-SEM and XRD were used to evaluate the physical/physicochemical properties of the nanofibers. Lastly, the lithium ion recovery was tested for the nanofibers with different physical properties using lithium ion solution. INTRODUCTION Demand for lithium resources is increasing in many industries across the world.1-2 However, the conventional resources for lithium is very limited, and it even gets worse to secure the resources due to low grade and/or complexity of feed materials. Much effort has been, therefore, devoted to obtaining lithium from aqueous lithium resources. Several methods such as solar evaporation3-4, co-precipitation5, and solvent extraction6 have been proposed for recovering lithium from an aqueous lithium source, but there are limitations on its use; It takes a very long time or conditions such as temperature, pH and Mg/Li ratio are severe. Lithium ion-sieve (LIS) materials are considered as a good lithium adsorbent because of their unique chemical structure that can selectively separate lithium ion from brine and seawater.7- 10 Furthermore, their low toxicity, low cost, and high chemical stability make LIS suitable for lithium recovery from aqueous lithium resources. Spinel hydrous manganese oxide (HMn2O4) derived from spinel lithium manganese oxide (LiMn2O4) after topotactically extracting lithium from the spinel structure by acid treatment is most widely investigated LIS.10, LIS materials have been actively studied in various forms for easy handling and high efficiency (i.e. membrane11,12, foam13-14, granular15,16). Among them, the 1-D nanostructure LIS with high specific surface area is excellent in efficiency.9 In this study, we present the part of our recently submitted work17. Specifically, we fabricated systemically lithium manganese oxide nanofibers with different diameter as a lithium ion adsorbent using electrospinning technique through design of experiment (DOE). Enhanced lithium ion adsorption properties of the HMn2O4 nanofibers with different diameter were investigated in lithium liquid resources."

Jan 1, 2018

By SUHAINA ISMAIL, NORLIA BAHARUN, SHAIK ABDUL RAHMAN, WAN NUR SYAFIQAH ANUAR, MOHAMMAD REZAEI ARDANI

Refractory gold ore contains sulfide minerals like pyrite, chalcopyrite and sphalerite that are difficult to be directly leached by cyanidation or by lixiviants such as thiourea and halides. In such cases, it is necessary to perform oxidative pretreatment of the ore to oxidize the sulfide matrix, and gold particles can be exposed to the solution during the leaching process [1]. In recent years, hypochlorite and chloride solutions have been introduced as alternative materials for hydrometallurgical methods of gold extraction instead of cyanide solution [2]. A previous study by Hasab et al. [3] reported that the gold dissolution rate in hypochlorite solution was higher than in the cyanidation process, due to the presence of hypochlorous acid (HOCl) as a strong oxidizing agent. In a hypochlorite leaching system, the change in pH can influence the presence of oxidant species in the solution: the hypochlorite ion (OCl−) is stable in pH greater than 7.5, HOCl can be found in pH between 4.0 and 7.5, and aqueous chlorine (Cl2 (aq)) is the predominant oxidant when pH is below 4.0. As HOCl is the most effective oxidizing agent for gold extraction, pH should be maintained in the range of HOCl stability [4].

By Warren D. Stanford Stanford

Introduction The Sleeper mine is a near-surface gold mine located in a remote area 56 km (35 air miles) northwest of Winnemucca, NV (Fig. 1). The deposit was discovered in 1984 by an Amax exploration geologist. Favorable drilling results led to feasibility studies and metallurgical testwork. Final evaluation of the mine potential proceeded very quickly. The project received Amax board approval in July 1985. Eight months later, the process plant was fully operational. The first gold ($1 million) was shipped one month later, in March 1986. Total plant capital was $27 million. Payback was achieved in six months. The Sleeper mine was expected to produce 1.6 t (53,000 oz) of gold and 1.3 t (41,000 oz) of silver annually. However, the ore body exceeded all expectations. Production for the first 10 months of operation amounted to 4 t (128,000 oz) of gold and 2.9 t (94,000 oz) of silver. Direct cash operating costs are in the $1.77/g ($55 per oz) range. Amax is actively conducting exploration nearby for additional reserves to extend the mine's life. (See update on page 242.) Geology The Sleeper gold deposit is located on the northwestern flank of the Slumbering Hills and in the Awakening Mining District. Rocks exposed in the vicinity of the deposit are interbedded siltstones, sandstones, and limestones of Triassic age. They are overlain by latite lava flows and tuffs of Tertiary age. Dikes and sills of latite and andesite intrude the sedimentary rocks. Quaternary deposits of mostly sand with minor gravel and clay cover a pediment containing the gold deposit. The sedimentary and volcanic rock units have been transsected and offset by extensive north- northeast trending faults and less abundant northwest trending faults. Both fault systems fractured and prepared the ground for subsequent invasions of mineral-bearing hot spring geothermal waters. The hot spring systems produced widespread hydrothermal alteration and gold mineralization at silicified centers near feeder fault structures. The deposit is hosted by siltstone and latite that have been hydrothermally brecciated. The main breccia is elongated north-northeasterly. The hydrothermal breccia zones appear to dip steeply to the west. Gold mineralization consists of native gold and electrum deposited in two or more high-grade quartz-breccia veins. Lower grade gold mineralization occurs

Jan 4, 1987

By Aline Tatom

This paper presents numerical and experimen¬tal results dealing with the application of ferric ion oxidation of uranium in acidic media. Conclusions are derived from matching numerical results to experimental data taken on one-dimensional laboratory leaches using ore from a South Texas Coastal plain deposit. Since the numerical results can be made quite general, we are able to extract and quantify the effects of oxidant concentration, flow velocity, mass transfer, chemical kinetics, and competitive oxidant consumers (pyrite and molybdenite) on the experimental results. Our results suggest that the leaching of uranium is a mass transfer controlled while that of pyrite is kinetically controlled.

Jan 1, 1981

By William L. Carter

Through your presence here this morning and your membership in the Society of Mining Engineers, you have shown that you are interested in keeping abreast of the latest technology and mining procedures, want to be part of the continuing progress made by those in your profession, and are looking for ways to participate in expanding your professional and personal experiences and skills. All of these factors are part of your continuing education, the need for peer identification or recognition, and the desire to make a specific contribution to strengthening your profession. However, you may be here with or without your company support and financial backing, unless you are self-employed. Whether you are here for the above reasons, or for many others, your presence reflects a recognition of the importance of participating in the organizational structure of your profession.

Jan 1, 1981

By M. L. Harris, J. Organiscak, S. Klima, I. E. Perera

"The National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Mining Research Division (PMRD) conducted underground evaluations in an attempt to quantify respirable rock dust generation when using an untreated rock dust and a rock dust treated with an anti-caking additive. Using PDM 3600s and 3700s, these evaluations measured respirable rock dust levels arising from a flinger-type application of rock dust on rib and roof surfaces. Rock dust with a majority of the respirable component removed was also applied in NIOSH’s Bruceton Experimental Mine (BEM) using a bantam duster. The respirable dust measurements obtained downwind from both of these tests are presented and discussed. This testing did not measure miners’ exposure to respirable coal mine dust under acceptable mining practices, but indicates the need for effective continuous administrative controls to be exercised when rock dusting to minimize the measured amount of rock dust in the sampling device. INTRODUCTION Two factors have combined to renew concern regarding respirable dust measurements and compliance. This renewed recognition is due to two regulations that have modified operators’ rock dust schedules. First, the 80% incombustible requirement in intake entries has increased both on-section and outby-the-section rock dusting. Secondly, the recent respirable dust regulation change that has increased the number of respirable dust samples taken per sampling cycle. Previously, when only 5 samples were needed bi-monthly, rock dusting could be scheduled to not interfere with the respirable dust sampling schedule. The significant number of samples now required under new regulations combined with the need to maintain 80% total incombustible content in active mining areas require the schedules for respirable dust sampling and rock dusting to intermix. This raises concerns about the amount of rock dust that potentially is included in the sampler weight gain. Additionally, the respirable dust maximum was lowered from 2.0 mg/m3 to 1.5 mg/m3 (effective August 1, 2016) increasing concern that rock dust contamination may be an issue. Currently, the acceptable practice is to apply administrative controls such as keeping the miners upwind during rock dust application or to schedule rock dusting during a maintenance shift when the number of miners present is lower. NIOSH’s research examining the quality of rock dust has led to the development of hydrophobic rock dusts."

Jan 1, 2017

By J. B. Hiskey, X. H. Jiang

The extraction of gold from chloride solutions by ion exchange is examined. It is shown that at initial gold concentrations between 1 - 5 ppm, 20 g/l C1- and pH 5, the kinetics of loading on weak base resins are slightly slower than those observed with activated charcoal. Equilibrium loading of auric chloride varies considerably as a function of pH from one resin to another. For all of the resins studied, nearly complete gold extraction was achieved between pH 2 and pH 6.5. Sodium hypochlorite was found to exhibit a slight effect on the equilibrium loading of gold chloride.

Jan 1, 1990

By W. M. Ma, Daniel W. H. Su, K. Centofanti, Yi Luo, W. L. Zhong, Syd S. Peng

8.1 INTRODUCTION Under room and pillar mining if the extraction ratio is low, (i.e., < 50%) a pillar can support the overburden without collapse and there will be no surface subsidence whatsoever. In other words, if the pillar sizes are properly determined to support the overburden weight, the roof strata cannot cave and there will be no surface subsidence, provided the entry width is small and properly reinforced so that a continuous roof fall leading to piping or the total collapse of the roof does not occur. Under the prevailing mining conditions in the US if only development mining is em¬ployed in room and pillar mining (i.e., no pillar extraction), the extraction ratio is usually less than 50% and generally no surface subsidence will occur. If pillar mining is employed, surface subsidence may occur, depending on the extraction ratio and the size of the remnant pillars (or stumps) left in the gob. The higher the extraction ratio, the smaller the stump pillars left behind in the gob. As the size of the stump pillars becomes smaller, the possibility of their support¬ing the roof without collapse is smaller. If all stumps are crushed completely, the roof will collapse and surface subsidence will occur. Again, whether surface subsidence occurs, it depends on whether the remaining stumps can support the overburden or not. Therefore, since the weight of the overburden which the stump pillars have to support is proportional to the mining depth, a fixed¬size stump pillar can support the overburden at a shallow depth, but will collapse under greater depths. In this context extraction ratio is not the only parameter for determining whether surface subsidence will occur. Furthermore, during pillar mining a pillar can be cut away in many ways to finally reach the same extraction ratio. Therefore, the safest way to determine whether or not sur¬face subsidence will occur in room and pillar mining is to compare the strength of all stump pillars in the panel of interest with the weight of the overburden that the pillars have to support. If they are too small to support the overburden, surface subsidence will occur. Under normal mining practices the characteristics of surface subsidence profiles vary with methods of mining. In the US there are two types of coal mining methods, i.e., longwall and room and pillar mining. Longwall mining is indisputably a total extraction method, but different percentages of coal recovery are achieved in room and pillar mining. Recovery is much higher for sections with pillar extraction than those without pillar extraction. For those without pillar extraction, coal recovery increases with increasing entry width or decreasing pillar size. For those with pillar extrac¬tion, the total coal recovery depends on the amount of coal ex¬tracted from each pillar which is in turn dependent on the roof conditions and methods of pillar extraction. Bauer and Hunt (1981) analyzed the characteristics of the subsidence profiles due to the three types of mining methods in Illinois. Fig. 8.1 shows the range of locations associated with the following profile features: profile edge, maximum tensile curvature, maximum slope, maxi¬mum compressive curvature, and maximum subsidence. The scat¬ter of the data increases with decreasing percentages of extraction. The profile is much sharper for longwall mining and becomes milder as percentage of extraction decreases; for longwall mining the profile edge is always beyond the opening, while in room and pillar mining it may fall within. The location of maximum tensile strain moves outward, while that of the maximum compressive strain moves inward as the percentage of extraction decreases and the maximum subsidence decreases with decreasing extraction ra¬tio. The general concepts discussed in this chapter may not apply to the entry development sections between two longwall panels where roof caving in both panels are very severe and overlap each other. Consequently, it must be treated differently. 8.2 CASE STUDIES Kohli et al. (1982) described several case studies on surface subsidence due to room and pillar mining with pillar extraction. In one case, the seam was 6 ft thick and ranged from 650 to 800 ft deep. The panel was 720 ft wide (Fig. 8.2) and was developed with seven entries. Each entry was 18 ft wide and the pillars were driven at 88 ft center-to-center between entries and crosscuts. Dur¬ing retreating, two additional pillars (pillars J and K) were devel¬oped, two blocks ahead of the pillar line, to take the barrier pillar, 160 ft wide, between panel No. I and No. 2. Pillar extraction began by taking a central slice across the whole panel, beginning from pillar 0 through J. After that, each pillar was sliced by 6 wing-slices, 3 on each side, leaving 4 stumps, 2 on each side. One of each pair was triangular shaped approximately 6 ft wide by 26 ft long. The other was trapezoidal, 26 ft long by 16 ft and 10 ft wide at the upper and lower bases, respectively. This resulted in a total extraction ratio of 85% within the panel. Obviously the stump pillars were not large enough to support the overburden and col¬lapsed completely. The final subsidence profiles were rather smooth, just like those under total extraction (Fig. 8.3). The max¬imum subsidence on Lines A and B was about 3 ft for an average mining height of 6 ft, but the locations of the maximum subsidence were skewed toward panel No. 1. Along Line D, the central por¬tion was flat-bottomed, but the maximum subsidence was only 2 ft, mainly because Line D was only two blocks from the right-side edge. Notice in every profile there was heaving of as much as 0.3 ft, beyond the edges above the solid coal. In another case (Fig. 8.4), the seam was 6 ft thick under 650 to 850 ft cover. Three panels, 710, 400, and 350 ft wide, respec¬tively, were extracted side by side. The entries were 18 ft wide and the pillars at 88 ft center-to-center between entries and crosscuts. Pillar extraction was practiced the same way as described previ¬ously. According to the mine maps, there was no barrier pillar left between the adjacent panels. Thus after extraction the three panels formed a common gob of more than 1460 ft wide. This was re¬flected in the development of the subsidence profile along the county road. After Panel No. I was mined, the maximum subsi¬dence of 1.2 ft occurred at Monument No. 1. This was increased to 1.6 ft after the extraction of Panel No. 2 and went to a further 1.8 ft after the extraction of Panel No. 3. The final maximum subsidence of 4.3 ft occurred at Monuments No. 6 through No. 8, while the remaining portion of the county road showed rebound. However it must be noted that the subsidence profiles were rather bumpy and fluctuated, perhaps an indication of the irregular stump pillars that were left and crushed at various time after mining. Moebs (1982) surveyed the subsidence profiles of four room

Jan 1, 1992

By R. G. Reddy

Viscosities of Feo-SiO2 slags were calculated using the previously developed structural based model. An expression was derived using hole theory and the atomic pair model to relate the NO0 and temperature to the viscosity. The deduced equation n=4.9x10-9 T1/2 NO0 exp (E/RT) poise was successfully applied to predict the viscosity of FeO-SiO2 slags in the composition range of 0.1 < XSiO2 < 1 for several temperatures. The calculated data agrees well with the experimental viscosity data.

Jan 1, 1991

By Paul H. Johnson

The CH Leaching process is a new, more sophisticated, form of gold, silver, uranium and sulfide copper heap leaching wherein each layer of a multi-layered heap is divided into a number of independent cells, each of which are successively formed and leached in the top layer of the heap to their maximum economic recoveries, and then rinsed and sealed from further leaching. Triangular earth berms form the outside walls of the heap and a gridwork of rock-filled berms on top of the bottom pad form independent under- heap solution storage zones. The high degree of solution recirculation and staging that occurs in this process produces a relatively small volume of very rich pregnant solution. The cellular heap design and its mode of operation result in a uniform, intensive, long-term leach for all of the ore particles in the heap. Besides improved metal recoveries, the process appears to have several cost and operating advantages. In the CR2MR process, sulfuric acid and a soluble sulfide are added to a gold and/or silver pregnant leach liquor to precipitate most of the contained silver, mercury, copper, etc. as sulfides at a pH below 2.5. The other product of the reaction is solubilized HCN. Following a liquid-solid separation step, cyanide is regenerated in the supernatant solution by raising the pH to a level above 9.0. This process regenerates a portion of the cyanide used in the leaching step, removes contaminant ion species (silver, copper, mercury, etc.) from the leach solution and, in a subsequent step, recovers the gold in an enriched form. It is believed that substantial cost savings may be experienced by the use of this process in some gold and/or silver leach systems.

Jan 1, 1984

By MARK J. VANARELLI

Estimating groundwater inflows in rock deep tunnels is critical to the safety of personnel constructing the tunnel and the cost of construction. This paper presents two case studies for estimating steady-state groundwater inflows into deep rock tunnels. The case studies included the Chattahoochee and Nancy Creek tunnels. In this paper, statistical methods were applied to packer test data obtained from exploratory borings during geotechnical site investigations. A semi-empirical procedure was utilized for estimating groundwater inflows into these deep rock tunnels. The Chattahoochee and Nancy Creek tunnels are deep rock tunnels which exhibit radial flow conditions. For the radial flow condition, a statistical analysis presented in this paper indicates that the semi-empirical procedure works well; however, variations in the procedure and/or an insufficient amount of testing could lead to underestimations of the inflow quantities. Packer test data plotted in histograms were observed in all cases to be log-normally distributed for the radial flow condition. Modeling using Monte Carlo simulations was observed to be an effective tool for removing irregularities in the distribution of the data and incorporating high-end permeability data to derive reasonable groundwater inflow estimates.

Jun 13, 2021

By M. Stephen Enders

The Little Rocky Mountains host epithermal gold-silver bearing vein and stockwork deposits in a syenite intrusive complex. Pegasus Gold Ltd. is currently mining the oxidized deposits by open-pit methods and recovering gold and silver by heap-leach processes. A geologic program has been designed to effectively determine the basic ore characteristics; 1)mineralization; 2)oxidation; 3)structural setting; 4)lithology; 5)alteration; and ultimately, 6)the leachability of the ore. Geologic mapping, sampling, drilling, assaying, and testing are routinely used in exploration, development, production control, mine planning, and ore reserve estimations. Timely and accurate assay results are essential for the program&apos;s success.

Jan 1, 1983

By Seung Han Kim, Andrew Yu, Carlos Jaramillo, Chu-Chieh Jay Lin

The Penstock Access Tunnel (PAT) concrete plug is a reinforced concrete plug separating the pressure tunnels from the personnel accessible tunnels and has leaked since the first filling at the Helms Pumped Storage Plant located in Fresno County, California. A grouting program was successfully implemented in 2009 to reduce the leakage from PAT concrete plug from over 1,000 gpm to 25 gpm. Recent observations indicated increasing water leakage through new pathways, leading to a decision to execute a high-pressure grouting and waterproof membrane installation program in 2017. The high-pressure grouting and membrane installation program was successfully executed in the areas adjacent to the PAT concrete plug where most of the inflows originated and the largest hydraulic gradients are suspected to present. It reduced the leakage from over 300 gpm of inflow to less than 20 gpm.

Jun 13, 2021

By Luke Clarkson, David Williams

The intent of this paper is to provide overview context to allow broader understanding of conventional tailings dam failure mechanisms. The research leverages global knowledge, experience, and data collection and interpretation for the safe and controlled management of the geotechnical stability of a tailings storage facility. The motivation for this review is to facilitate transparent access to tailings dam background and understanding. This paper addresses the core understanding of geotechnical failure mechanisms, and how these eventuate to instability and failure of tailings dam structures. This research focuses on foundation failure, internal erosion and piping, overtopping, seepage, seismicity, and slope instability and provides insight into what factors contribute to failure, how failure progresses due to such failure, anticipating and monitoring for the aforementioned failure modes, and designing to mitigate their risk.

Feb 15, 2021

By Syd S. Peng

According to accident statistics (l, 2), roof fall accidents occur quite frequently at the intersections of underground? openings and account for up to 30% of the roof fall fatalities. But this figure will certainly go up considerably if roof falls not associated with any fatal accident are included in the analysis. Unfortunately, nonfatal roof falls are seldom documented. In the underground coal mines, there are two types of entry intersections. One is the three-way (V type) and the other is the four-way (T type) intersections. A three-way intersection occurs whenever the mainline track haulageway turns at an angle into a section haulageway. The four-way intersections by far the most common type in the U.S. under-ground coal mines are formed by the intersections of two entries which are oriented perpendicular to each other or by the intersections of entries and crosscuts. However, crosscuts are frequently driven at an angle to the entry to facilitate machine movements. The four-way intersections formed by this method of crosscut development are angled. At the intersection of two underground openings, the diagonal roof span is wider than the width of each individual opening. This is one of the major reasons why roof falls occur more likely at the intersections than in the entry between pillars. Consequently, special intersection support plans are usually employed (Figs. 1 and 2) for intersections. The most popular practices are to decrease roof bolt spacing 1 ft. less than or to increase roof bolt length 1 to 2 ft. longer than those employed in the entry between pillars (3). The increase in bolt length or decrease in bolt spacing can be applied to all of the bolts in the intersection or employed only for the strategically located bolts depending on the individual mine practices. These rather generalized practices seems to be adequate for some areas but in many cases inadequate for others. Occasionally, the neighboring two lines of chain pillars are staggered such that the crosscuts in one row of chain pillars face the centers of the chain pillars in the neigh-boring rows. This layout forms T-type three-way intersections which are also inadequate for most weak roofs (3, 4). A study was therefore initiated to develop special techniques for intersection supports. The first phase of the study was the analysis of the stress fields for the underground entry intersections. A three-dimensional stress analysis was necessary for this purpose. Unfortunately, the three-dimensional problems of complicated boundary conditions are beyond the existing analytical methods. The three-dimensional finite element method (FEM) was therefore employed in this study. In the analysis, square pillars of 40 feet wide and an entry height of 8 feet were assumed while entry widths varied at 14, 20 and 26 feet. This model was selected to simulate the mine where roof falls data were collected. The second phase of the study was the collection of field data. The sizes of the roof falls including heights, lengths and widths were collected and analyzed. In the third phase study, the results of the first and second phases were compared and discussed. The analysis of field data revealed an arching zone within which roof falls occurred. The arching zone above an entry obtained empirically was compared with the calculated stress contours. Assuming that the bolts must be anchored in the rock strata outside the arching zone, the preferable systems of bolting were proposed. Also the amount of pretension required to inhibit sliding between layers was discussed.

Jan 1, 1978

By K. F. Unrug

An overview of the history of mining technology, both past and present, shows that some of the new concepts being successfully applied have changed the reserve categorization and are having an overall impact on production. Past coal mining operations in the eastern coal fields, and especially in Appalachia, extensively utilized stripping with the predominately applied contour method. As a result, vast mountainous areas have abandoned benches left behind by past mining operations. While thicker seams previously stripped were usually mined by underground or mountain top removal methods, thin seams beyond technical or economical limits were left intact after contour mining had reached the ultimate height of the wall. These thin seams quite often contain high BTU, low ash and sulfur coal that makes them attractive for a secondary recovery due to the market requirements. Secondary highwall recovery has obvious potential and is economically attractive; however, with the present state of industrial experience and lack of analysis of site data, a trial and error approach is used by operators.

Jan 1, 1983

By M. L. Harris

Coal dust produced during the mining process is a prime explosion hazard in underground coal mines. To inert the coal dust and prevent a catastrophic propagating dust explosion, rock dust is applied to the roof, ribs, and floor surfaces of mine entries. Currently, one determination of whether a mine is adequately protected from the coal dust explosion hazard is made by analyzing collected mine dust samples for percent total incombustible content (% TIC). A minimum of 80% TIC is required per 30 CFR 75.403. The as-received moisture of the dust sample is included in the % TIC. Moisture and humidity within a coal mine vary greatly with the seasons, with explosions occurring more frequently during dry winter months. This paper will discuss the fluctuations of the as-received moisture content of the mine dust samples collected by U.S. Mine Safety and Health Administration inspectors in 2010 and the observed fluctuations of the moisture content of rock dust within the U.S. National Institute for Occupational Safety and Health Office of Mining Safety and Health Research Bruceton Experimental Mine and the Safety Research Coal Mine over a one-year period.

By H. Zhu

Qualitative and interpretative information as obtained from geological and/or geophysical studies, in addition to precise measurement, is incorporated into the estimation process through an indicator variable. The indicator conditioned estimator is formulated as a cokriging and its expression is data value dependent as opposed to that of the traditional kriging estimators. The solution of the dual cokriging system pro-vides simultaneously an estimate of the unknown and an estimate of the conditional probability that the unknown belongs to a specific population or class. Being an unbiased and minimum-error-variance estimator by construction, the indicator conditioned estimator is better in the least square sense than the ordinary kriging estimator because it uses additional information carried by the indicator data.

Jan 1, 1989

By J. M. Wempen, R. D. WEYHER, M. K. McCarter

Beam theory is a proxy for the behavior of intact, deforming roof strata above underground openings. Strong, stiff, intact strata have the ability to store significant strain energy when underground openings have large spans, as is typical of longwall operations. When strata fail, they may release some or all of this strain energy. Released energy is partitioned between fracture, thermal, and seismic energy. The tensile failure surface in simply supported beams is predicted to be free of shear stress. This prediction and the kinematic inability of crack slip during fracture make significant dissipation of energy by friction unlikely. In this study, the failure energy partitioning of Nugget Sandstone specimens is examined. Tensile fractures in specimens were induced using three-point loading tests. Elastic waves emanating from fracture events were recorded using an array of accelerometers. Accelerometers were placed within two crack lengths of the fracture surface, and the acceleration records are similar to strong motion seismic records. Spectral analysis was performed and used to develop synthetic, well-behaved, acceleration signals. Synthetic velocity signals were used to estimate radiated seismic energy generated by fracture. These estimates of radiated seismic energy demonstrate a potential means to constrain the minimum seismic partition. Fracture testing was performed on additional samples to estimate the fracture toughness of the sandstone. Synthesis of this data demonstrate a potential means to constrain a maximum seismic partition. Bounding the seismic partition for this type of fracture event could aid the detection and evaluation of seismicity emanating from longwall operations. Having better information about the location and magnitude of mining-induced seismicity within longwall overburdens could lead to better understanding of extraction sequencing and rock behavior in general. These energy estimates also support the hypothesis that dissipation of thermal energy by friction is small in bending tensile failure.

Jul 1, 2020