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By Peter Swanson

One of the primary methods for analyzing roof stability in underground mines is the age-old method of “roof sounding” where a miner taps on the roof and listens for the hollow sound of loose blocks of rock. This paper looks at the feasibility of using noncontact laser-based vibration measurements to detect roof fall hazards with the ultimate vision of improving, expanding and automating procedures for mine roof inspection. Vibration measurements made on loose blocks of rock in underground mines are summarized and compared to estimates of fundamental resonance frequencies for rock slabs of the size responsible for highly hazardous “skin failures.” Both laser Doppler vibrometry and full-field interferometric methods are examined and are considered to be feasible methods for detecting anomalous vibrations in loose roof rocks. Results from simple laboratory experiments using laser vibrometry demonstrate some of the proposed application concepts. While considered a challenge to move these techniques from the laboratory to heavy industrial or outdoor environments, the potential for success in the current application is enhanced by the reduced requirements of qualitative analyses.

By E. E. Ungar

Criteria applicable to noise in coal cleaning plants are presented, and the generally applicable noise control principles and approaches are discussed. The operating characteristics and equipment of coal cleaning plants are described. Considerations entering in the selection and design of noise control means are delineated, and specific means for equipment noise reduction are described. The limited utility of acoustically absorptive materials in plant spaces is indicated, administrative means for reducing worker noise exposure are pointed out, and ear-protective devices are described briefly. The reduction of plant noise reaching nearby communities is discussed. Programs leading to quieter machines an coal cleaning plants are suggested.

Jan 1, 1974

By F. S. Kendorski

This report presents the results of a program to improve, using existing and proven technology, unstable highwall conditions through better blasting practices in Appalachian strip coal mines. Better borehole blasting agent distribution and optimization of burden, spacing, and delay periods allowing satisfactory breakage with minimal backbreak were the objectives. At a selected field site, geologic conditions were closely examined with regard to joint orientation and spacing, and resulting slope stability considerations. A test series of eight blasts was completed and the resultant highwall monitored by repetitive photography. The study of drilling and blasting economics along with equipment performance led to an economic model of blast parameters and the identification of blast design cost benefits. The work demonstrated that small strip mining companies' are able to achieve a more stable highwall excavation utilizing presently available technology, equipment, and explosive products at improved operational cost and safety.

Jan 1, 1981

By K. Y. Haramy

Coal mine bumps involve the violent, rapid failure of coal and rock around a mine excavation. Deep coal mines with strong roof and floor rocks and high-stress conditions frequently experience face and rib bumps. The bump problem is becoming more severe as mining depth increases, prompting efforts to control high stress in advance of mining. This Bureau of Mines report presents a review of the most widely used methods to detect and destress high-stress zones along coal faces and an investigation of stress-related bump problems and destressing techniques at a cooperating mine. Geotechnical instrumentation and microseismic methods were used to better understand bump occurrences in underground coal mines. Laboratory tests of the drilling-yield method for high-stress detection were conducted to determine the correlation between the volume of cuttings obtained and the magnitude of the applied stress at various confining pressures. A three-dimensional, multiple-seam computer modeling program, MULSIM, was used to evaluate the effectiveness of stress-relief methods. Modeling results indicate that dangerously high-stress areas can be controlled by either proper planning or destressing. Proper mine planning guidelines and destressing methods such as volley firing, hydraulic fracturing, and auger drilling are discussed.

Jan 1, 1988

By R. Karl Zipf, Kousick Biswas

The main objective of occupational health and safety research is to minimize or eliminate the events that may cause fatal or non-fatal injuries to human workers. A commonly used technique is to devise an “incident prevention plan”, which is more often the product of thorough investigations of past reported incident events. Incident documentation and methodical reporting and systematic and thorough data collection, often help identify the root cause of the incident – in other words, the etiology of the incident. These retrospective analyses of the incidents can efficiently identify the future steps to take to achieve the objective of minimizing occurrence of “events of interest”. This paper introduces a novel technique – “Taxonomic Analysis”, which identifies the root causes of an event (an incident in this case) and can provide future direction for corrective measures to reduce the probability of occurrence of the event. A taxonomic analysis involves systematic and organization of data based on observation, description, and classification. This paper utilizes the rock fall related incident narratives, available with the Mine Safety and Health Administration (MSHA) database (1984-1999), for a taxonomic analysis. The study found that 67.6% of groundfall incidents occurred in supported areas with the remainder (32.4%) in unsupported areas. Some form of rock mass failure appears to cause about 50% of groundfall incidents, although in 39.7% of the overall groundfall incidents or two-thirds of those involving rock mass failure, the exact nature of the rock mass failure could not be determined from the narratives. Human activities factors such as scaling or barring down, drilling or bolting, and setting timbers or cribbing accounted for another 34.5% of the groundfall incidents. Finally, support system failures made up the remaining 15.5%. Results from this taxonomic analysis may suggest focus areas toward which preventive measures and future research activities could concentrate.

By J. E. Urosek, K. L. Cashdollar, D. A. Beiter, G. J. Shemon

The National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MSHA) conducted joint research to evaluate explosion blast effects on mine ventilation stoppings at the NIOSH Lake Lynn Experimental Mine (LLEM). After mine explosion accidents, MSHA conducts investigations to determine the cause(s) as a means to mitigate or eliminate future occurrences. As part of these post-explosion investigations, the condition of underground stoppings, including the debris from damaged stoppings, are documented as evidence of the strength and the direction of the explosion forces. The LLEM data showed that a total pressure of 52 kPa (7.6 psi) destroyed the solid concrete block stopping, ~36 kPa (~5.2 psi) destroyed the hollow-core concrete block stopping, and 9 kPa (1.3 psi) destroyed the steel panel stopping. These results will assist investigators in determining the explosion forces that destroy or damage stoppings during actual coal mine explosions.

By Robert Stefanko

The growing demand for energy during the post World War I and World War II periods has prompted underground coal production to increase rapidly. This has been met primarily by mine mechanization, resulting in the development and application of new mining machine types. Correspondingly, the total connected horsepower of each machine as well as the number employed has enlarged rapidly since 1950. (2,3,9,14,16,17) Electrical consumption for each mine has also grown. In the early years of mining electrical applications, only d-c power was utilized underground. Yet, d-c machine limitations were soon realized, and many a-c systems were substituted to permit economic and efficient utilization of a-c distribution and motors. Due to the attractive torque characteristics, ease of distribution and speed control, several traction applications have continued to be powered by d-c motors. The result has been the now prevalent use of mixed a-c/d-c mine power. However, augmented electrical power employment seems to have added to underground coal mining electrical accidents.

Jan 1, 1974

By P. B. Ritter

The feasibility of redesigning and adapting the all- secondary-explosive, low-voltage, electric safe detonator for use as a delay detonator has been demonstrated. Experimental results have shown that operational characteristics can be adjusted to allow direct competition of safe delay detonators with commercial delay blasting caps. Five different experimental delay period models have been developed and tested. Test results are given and results are evaluated. Subsequent simplified and improved designs for practical and economical mass production are described. Design concepts to meet Bureau of Mines voltage withstand, incendivity, and spark sensitivity requirements are included. Recommendations are made for experimental procedures to ready the safe delay detonator for mass production and extensive use in mining and other industries.

Jan 1, 1977

By Thomas M. Barczak

Secondary roof support systems play a vital role in preserving the safety of underground mine workers by preventing the unintentional collapse of the mine roof. Hundreds of thousands of standing roof supports are constructed each year in underground coal mines. Historically, wood and concrete cribs and timber posts have been used for secondary roof support. These support constructions require the handling of heavy and bulky materials, causing numerous injuries to the mine workers and resulting in more than 40,000 lost workdays in the past 9 years. Since 1993, various alternative support technologies have been developed. These new support technologies not only provide superior roof support, but many also have significant material handling advantages by using smaller and lighter weight materials, fewer components, mechanically installed support systems, and pumpable support systems. The National Institute for Occupational Safety and Health (NIOSH) has conducted extensive material handling research and has developed recommended lifting thresholds to reduce material handling injuries. An analysis of roof support construction reveals that conventional support materials used in wood and concrete cribbing exceed the recommended lifting thresholds, while the engineered support systems are closer to the recommended weight thresholds. Finally, recommendations are made relative to proper lifting techniques and material handling practices to prevent injury to mine workers when constructing roof supports in underground coal mines.

Jan 10, 2000

By J. R. McVey

A 10-channel automatic data acquisition system has been designed and environmentally packaged for use with underground strain-gage applications and associated instruments. The system uses commercially available components and is assembled in two plastic enclosures. Environmental control is provided through a specially designed (compressed-air) air-conditioning system and water-resistant cabling. Accuracies of 0.01 pct and resolution of 1 µV have been obtained in underground tests.

Jan 1, 1973

By K. K. Kelley

Thermodynamics data for silicates have applications in the fields of extractive metallurgy, ceramics, and geochemistry. To facilitate these applications, up-to-date tables of heats and free energies of formation are needed. It is the purpose of this report to supply such tables for anhydrous silicates. During the last 15 years the heats of formation of a substantial number of anhydrous silicates have been reliably determined at or near room temperature. This resulted from the development (first by the Bureau of Mines and later by the Geophysical Laboratory of the Carnegie Institution of Washington, by the Institute of Geology of the University of Helsinki, Finland, and by the Department of Geology of the University of Chicago) of accurate solution calorimeters, employing hydrofluoric acid as the reaction medium. Specific references to work of these laboratories will be made in the next section of this report. Also, entropy data at 298.150 K. and high-temperature heat-content values are available for many of these silicates, mainly owing to work of the Bureau of Mines. Most of these entropy and heat-content data have been compiled in Bureau of Mines Bulletins (13, 15).3

Jan 1, 1962

By R. Barany

This report contains the results of experimental work conducted by the Bureau of Mines to obtain the heats of formation at 298.15° K. of analcite, dehydrated analcite, lawsonite, anorthite, hexagonal anorthite, and leonhardite. Thermodynamic data for these minerals have applications in ceramics, extractive metallurgy, and particularly in geochemistry. Except for data on anorthite, no previous similar data existed. The present results will be a substantial aid in deriving the temperature-pressure-equilibrium relationships among these minerals. The heats of formation were determined by solution calorimetry, with hydrofluoric acid as the reaction medium. The results were expressed both in terms of the constituent oxides and in terms of the constituent elements. The heat of formation data were combined with related entropy values to obtain the free energies of formation at 298.15° K.

Jan 1, 1962

By Keith A. Heasley, Timotlly M. Barton

Historically, the surface subsidence over underground coal mines has been predicted using empirical profile or influence functions which have little or no connection to the actual mechanics of the subsidence- Without a mechanistic basis, establishing the exact site-specific parameters to use in these empirical methods has been problematic. A practical subsidence predictive method based on mechanics has the appealing capability of allowing the determination of site-specific parameters from fundamental properties of the overburden with minimal field calibration work. This paper presents a case study where a mechanics-based, boundary-element program is used to calculate the surface subsidence associated with several panels of a Northern Appalachian longwall coal mine. The program used in this case study is called LAMODEL, and it incorporates a frictionless, laminated overburden into a general purpose displacement-discontinuity code primarily designed for calculating the stresses and displacements in coal mines or other thin seam or vein type deposits. In this paper. the program is used to calculate both the underground convergence and the resulting surface subsidence at three longwalls. The subsidence results from the model are compared with field measurements and analyzed The results from the case study in this paper demonstrate that the laminated model with calibrated properties can easily provide fairly accurate subsidence predictions and is fairly flexible for fitting measured subsidence. However, additional subsidence predictive case studies are recommended in order to ultimately evaluate the potential of the laminated overburden model for practical subsidence prediction

By W. R. Reed, J. A. Organiscak

Haul trucks have the potential to generate large amounts of respirable dust. This respirable dust has been shown to be a health hazard to personnel, especially if it has a high silica content. Lack of dust sampling data from haul trucks prompted the completion of a study to quantify respirable dust concentrations. These field studies were conducted measuring instantaneous respirable dust at stationary locations from passing haul trucks at a stone quarry and at a coal mine site. Fugitive dust levels from haul trucks were analyzed to characterize dust dispersion. This analysis indicates safe following distances for haul trucks and other heavy equipment to avoid overexposure of respirable dust from the lead haul truck.

By Thornton L. Neathery

Geologic investigation of a mineralized zone in eastern Alabama indicates that large quantities of talc and soapstone are scattered over a wide area close to the surface. Laboratory experiments show that this material may be upgraded to a high-quality talc. A market survey indicates that the talc deposits may be of current and long-range interest. The anthophyllite asbestos which is associated with the talc does not appear to occur in sufficient quantities to be considered as a primary commercial source.

Jan 1, 1967

The condition of the domestic mining industry is obviously affected by the cycles in general business conditions. This study, the results of which are presented in a series of 78 charts, attempts to examine the interrelationships between the general business indicators and the major statistical measures for the base-metals industries during the cycles in the United States economy following World War II. For these industries the cyclical problem is perhaps less acute than the secular-trend problem. However, short-run fluctuations in production and employment do have very important impacts upon the welfare of the regions which derive a significant portion of their income from base-metals mining and processing industries. Any information concerning the normal patterns of development as the industries enter into a cyclical recession will permit better forecasts and perhaps help promote measures to alleviate the distress that occurs. Also, a systematic study of the comparative movements among the statistical measures during a series of cycles can bring to the fore the economic causation involved, and perhaps, after intensive study, can lead to a better method of short-range forecasting for these industries. This study has not fully achieved these aims. However, observations which significantly aid the interpretation of the current monthly statistics on these commodities are made, and some very general conclusions are drawn. The charts are presented so the interested people can examine them and draw additional conclusions. The charts refer specifically to cyclical analysis. The technique of indexing each cycle to its turning point effectively subordinates the longer term trend movements of the data. Thus, certain general conclusions flowing from this study and from the continuing economic research of the Office of Chief Economist will aid the reader by clarifying the frame of reference within which the charts should be examined.

Jan 1, 1961

By H. B. Carroll

The performance of commercially available portable instrumentation for detecting nitrogen dioxide, sulfur dioxide, and hydrogen sulfide was evaluated. Length-of-stain detector tubes from several manufacturers were included in the study. The instruments were evaluated in atmospheres with 50-and 80-percent relative humidities at 75° F and containing test gas concentrations of 0.1, 0.25, 0.50, 1.0, 1.5, and 2.0 times the threshold limit values. The results from the gas analyzers were correlated with the known contaminant concentration by calculating and plotting an estimated line of regression, confidence limits, and correlation coefficient for each detector system. An increase in the relative humidity from 50 to 80 percent at /5° F changed the instrument response to the contaminants. The uncertainties in detection precision reported are for the observer-instrument system. The main difference or inconsistency in toxic gas concentrations determined with length-of-stain tubes resulted from the observer's interpretation of the results rather than from a predominant difference in the tubes.

Jan 1, 1975

By Maurice C. Fuerstenau

The kinetics of leaching galena with ferric chloride and ferric nitrate have been examined as a function of ferric concentration, salt concentration, temperature and particle size. Diffusivity of ferric complex ions was also established as a function of ferric chloride concentration and temperature. In the presence of 3 M NaCl, leaching rate is controlled by product layer diffusion when ferric chloride is added as oxidant. With NaCl concentrations less than 3 mole/liter rate decreases with decreased NaCl concentration, and, thus, rate is apparently not controlled by product layer diffusion. It is suggested that rate is controlled by lead chloride solubility at the reaction interface under these conditions. When ferric nitrate is added as oxidant, leaching rate is limited by chemical reaction control. An electrochemical model is presented. Activation energies are 8.1 and 11.3 kcal/mol in the ferric chloride and ferric nitrate systems, respectively.

Jan 1, 1984

By Ren G. Dong, Jay Kim, Daniel E. Welcome, Won Joon Song, Charles Hayden

Prolonged, extensive exposure to hand-transmitted vibration could cause a series of vibration-induced disorders in the vascular, sensorineural, and musculoskeletal structures of the human hand-arm system, which have been collectively called hand-arm vibration syndrome (HAVS).1 To assess the risk of HAVS the international standard ISO 5349-1 (2001)1 recommends using the root-mean-square (rms) acceleration of the measured vibration with a frequency weighting. While a few epidemiological studies have reported results consistent with the predictions made according to the recommendation, many other studies have reported results with large discrepancies.2 This may be partially attributed to the time-averaging effect involved in calculation of the frequency components, especially for impact type tools. Because the spectral characteristics of impact tools change dramatically with time, a time-frequency (T-F) analysis can provide better characterizations of such highly transient vibrations. The analytic wavelet transform (AWT) is an ideal T-F analysis tool because it possesses the advantages of both the Fourier transform and the wavelet transform.3 The objective of this study was to explore the application of the AWT method for characterizing the impact tool vibrations and assessing their exposure risk. Methods Five tools (two chipping hammers, two riveting hammers, and one concrete cutting saw) were used in this study. The saw vibration was measured when it was used to cut a section of road pavement during a repair. The vibrations on the other tools were measured by the procedure specified in ISO 8662-2 (1992).4 A sampling rate of 16,386 Hz was used in the measurement. The AWT and Fourier analysis were applied to these signals and to identify their characteristics. Results Figure 1 compares the T-F characteristics of the accelerations measured from the relatively steady concrete saw and a riveting hammer. The frequency weighting specified in ISO 5349-11 was applied in the calculations. The comparison clearly shows that the two tools have completely different T-F characteristics.

Jan 6, 2006

By Stephen C. Tadolini, Yunqing Zhang, Thomas M. Barczak

Standing crib supports have been applied in underground mining programs to resist large roof movements and sustain high-loads. The strength and deformation capability of these systems has been documented under both laboratory and field conditions. The parameter that has not been examined and is not well understood is the effect that a crib or other types of standing support has on the primary and secondary bolting systems. A crib support system with low system stiffness may allow large amounts of closure and deformation and cause the bolting systems to yield or even fail. Conversely, cribs or standing support that are too stiff may experience brittle or buckling failures, negating the advantage of the intrinsic supports previously installed. Utilizing a combination of field measurements and 3-dimensional finite element modeling techniques, the relationship between system stiffness and the subsequent performance of the installed bolting system is evaluated. Additionally, a simple method for calculating the combined system stiffness for standing supports, when using materials with different strengths such as steel, concrete, wood, etc., is presented.