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By S. A. Lolon, J. F. Brune

"INTRODUCTION In underground longwall coal mining, the mined-out areas or gobs frequently contain methane which can form explosive methane-air mixtures. Historically, there have been many events of mine fires and explosions recorded in the United States and other countries that have demonstrated the existence of such explosive mixtures, herein referred to as Explosive Gas Zones (EGZs), inside and around the perimeter of bleeder-ventilated longwall gobs (Loane et al., 1975; Lynn et al., 1986; Elkins, et al., 2001; McKinney et al., 2001; Dziurzynski and Wasilewski, 2012; Brune, 2013). The risk of mine explosions can increase if the EGZs migrate out from the gob into the surrounding mine entries. Several factors can induce EGZs outflowing from the gob, but the most common cause is the fluctuating barometric pressure. Atmospheric pressures change regularly every day but can fluctuate abruptly and become increasingly hazardous in adverse weather conditions. Other sudden pressure changes can result from roof falls, failing ventilation controls and fan outages. Any such fluctuation of mine ventilation pressure will disturb the pressure differential between the gob and the surrounding mine workings and may cause EGZs to outgas from the gob. The correlation between major mine explosions and abrupt barometric pressure changes has been studied and confirmed for explosions in coal mining countries including the United States, South Africa, Australia, and Poland (Hosler, 1948; Boyer, 1964; Kissell et al., 1973; Fauconnier, 1992; Hemp, 1994; Wasilewski, 2014; Belle, 2014; and Lolon, 2017). Disastrous mine explosions appear to happen more frequently during stormy weather, which, in the United States, typically occurs during the late fall and winter seasons. ROOT CAUSE AND EFFECT OF GOB BREATHING Gob breathing is the result of the pressure differential between gob internal and external pressures caused by external atmospheric pressure fluctuations that occur naturally as a result of gravitational and thermal forces in the atmosphere (Lindzen and Chapman, 1969). Other major and sudden pressure changes may be caused by fan failures, failures of ventilation controls or roof falls can also cause an unexpected gob breathing. Normal barometric fluctuations occur every day but usually do not pose an explosion risk as they occur gradually so gob pressures have sufficient time to equilibrate. More extreme fluctuations associated with cyclonic weather systems and storms often result in more rapid and larger drops or rises in barometric pressure (Hosler, 1948; Fauconnier, 1992). A study by Lolon (2017) found that the timing of historical mine explosions showed consistency with the occurrence of abrupt and intense barometric variations."

Jan 1, 2018

By Wescomb R. Jones

The United States is the world's largest producer of hydrofluoric acid (HF), with its 1971 output of 317,000 short tons representing about 40 percent of the estimated Free World production. U. S. production has increased over five fold in the past 20 years, with a growth rate of about 7 percent per year between 1960 and 1970. However, the growth rate to 1977 is expected to be less than 5 percent per year, due primarily to a reduced rate of growth in requirements by the aluminum industry and an expected increase in imports from Canada and Mexico. This discussion will include our analyses of the consumption pattern for HF in 1972 and the factors influencing the demand forecast for 1977.

Jan 1, 1973

By J. Noll, A. Miller, J. Volkwein, C. Pritchard

Hecla Limited, Magee Scientific, and NIOSH have combined efforts to evaluate an in-situ air filtration system for use in an underground mine environment. The purpose of the collaboration was to determine the efficacy of such a technology for reducing the concentration of airborne diesel particulate matter (DPM), with the aim of improving air quality in underground hardrock mines. A secondary goal was to evaluate the use of an Aethalometer as a means of real-time measurement of black carbon as a surrogate for DPM. The evaluation included measuring the DPM-capture efficiency of the filter when it was pre-loaded with dust. Toward this end, rock dust was introduced at the filter inlet to create a dust layer on the filter surface, with the intent of providing improved capture of the much smaller DPM particles. The filtration efficiency for DPM was assessed by comparing measurements of DPM taken at the inlet and outlet of the system, using both real-time and time-weighted-average approaches. The real-time measurements were performed with the model AE33 Aethalometer® made by Magee Scientific. The results of the NIOSH 5040 method analysis were used to assess the effects of the system on time-weighted-average concentrations of total carbon. Results showed a reduction in DPM concentrations in the range of 82%-89%. While the calculated efficiencies based on the two different measurement methods were similar, the DPM levels reported by the Aethalometer were higher, possibly due to differences in the performance of the size-selectors used for the two methods (impactors versus cyclones). More research is required to develop a robust correlation between the two methods, to support the use of the Aethalometer for future mining applications. The advantage of the Aethalometer is that it can measure and record DPM levels for weeks at a time, and can be directly connected to a mine monitoring system, potentially at multiple locations. Ideally such data can be used to initiate the startup of the filtration system should DPM concentrations reach an action level. This work demonstrated that in-situ filtration systems, modified to collect DPM and coupled with real-time monitoring, show promise at reducing DPM concentrations in the mine environment.

Jan 1, 2016

By R. V. Stewart

This chrysotile asbestos orebody is located near the northern tip of the Province of Quebec, Canada. It is some 1818 km (1130 mi) north of Montreal; 480 km (300 mi) north of the tree line and is situated within the zone of continuous permafrost. The open pit ore zone is approximately 0.4 km (1/4 mi) in length some 61 m (200 ft) in width and plunges at 25-30 below surface to a vertical depth of at least 610 m (2000 ft). The orebody was originally evaluated by programs of surface mapping, diamond drilling and bulk sampling. The fibre is semi-crude, possesses excellent strength, and good fibre length distribution.

Jan 1, 1978

By Cleland N. Conwell

The term "tender tundra" is a myth---a well-developed myth, but contrary to the fact. Any area that supports herbivores must have a plant base to supply food, In Alaska, herds of caribou migrate and live north of the Arctic Circle. And, if there is enough growth in the moss and lichens and arctic grass to support a caribou herd, the "tender tundra" can heal after it has been disturbed by mining. Another myth is that Alaska is an ice box. Actually, many areas In the state---particularly the Interior---have a high agricultural potential. Nevertheless, the fact remains: whether it is reclaimed by advancing the productivity from forest to agriculture or is allowed to remain a wild-life habitat, Alaskan land will revegetate. Reseeding speeds reclamation, but left to nature, native species will reclaim the land whether it was disturbed by forest fires, roads, villages, or mining. In fact, it is impossible to find many of the old gold mining camps.

Jan 1, 1975

By Howard W. Adam

Mill length was the primary variable investigated in an autogenous pilot mill circuit. The 5-1/2' diameter mill had both pebble ports and 1/2" wide slotted grates. The plus 1/2" mill product was crushed in a cone crusher and returned to the mill feed along with the minus 1/2" plus 4 or 6 mesh fraction. Tests were run with a short mill, inside length of 26-3/8", or diameter-to-length ratio of 2.50 to 1. The same mill was then lengthened to 48-3/8", diameter-to-length ratio of 1.36 to 1. The effect of mill length on circuit product characteristics was studied. Results show that (1) circuit throughput or grinding rate is lower per foot of mill length in the longer mill, (2) the long mill product is finer than the short mill product, and (3) KWH per ton of circuit product is slightly higher with the longer mill; however, KWH per ton of minus 200 mesh material (finer fraction) produced is essentially the same in the long mill as the short mill, It is not known whether the relationships found for the pilot mill are valid for commercial size mills.

Jan 1, 1973

By David S. Young

All pigments and extenders or fillers whether organic or inorganic fall into the following broad general classes: I. Colored II.-White III. Black IV. Metallic A pigment- is any particulate matter that is essentially insoluble and chemically unaffected by the media into which it is dispersed. According to this very broad definition, colored pigments, white pigments, fillers, extenders, and functional pigments would all be included. The particulate size range would also be quite broad ranging from very fine colloidal particles (~0.01µ) to relatively coarse particles (~100.0µ). This broad definition is usually subdivided into more practical divisions which tend to relate the classification of the pigment to its primary function in the system in which it is used. Hence, the word extender implies that its major purpose may be to extend the system.

Jan 1, 1985

By M. Zaske, E. R. Mortensen

"As mine operators continuously look for ways to improve functionality and increase the capacity of their facilities, existing process equipment is often pushed to and past its designed limitations. As a result, equipment manufacturers are asked for economical solutions to meet redefined processing needs. Newmont Mining in Nevada was faced with such a need in its carbon-in-leach (CIL) train. In a collaborative effort between Newmont and Derrick Corp., tests were conceived to assess the viability of drop-in replacement screens using a three-dimensional screen panel. The synthetic pyramid screen panel was designed to increase flux while maintaining the existing equipment footprint. The test is the end result of an ongoing research and development project that Derrick undertook in an effort to refine and upgrade its urethane screening media. The application of this new screening media is presented for this CIL application along with future plans to implement the technology in trash, safety, carbon dewatering, carbon sizing and other scalping applications.In spring 2014, Process Machinery Associates (PMA), Derrick’s local area representative, met with Newmont to discuss the operation of the in tank screens in the CIL train at Twin Creeks, near Golconda, NV. The process was originally designed for about 12+ kt/d (13,000+ stpd) but the throughput has been steadily rising since the plant was commissioned. Newmont now requires 14.5 kt/d (16,000 stpd) to be processed. The original screens were running at their maximum capacity, and Newmont required additional screening capacity to continue the upward trend in production.Physical separation by use of screening is one of mineral processing’s oldest methods. Screening media can be prone to blinding and pegging, and the necessary support structures required for finer apertures result in smaller open areas. Therefore, more screening area generally requires larger panels and, thus, larger machines, screening media that does not blind or a combination of both.In an effort to avoid larger machines, Derrick had been working on a revolutionary threedimensional panel that would add nonblinding screen area in the same footprint of an existing machine. Alpha testing of the new screen panels began at Newmont Mill 2/5 in July of 2013. It was still occurring when PMA approached Twin Creeks about beta testing a refined machine and pyramid panel. After presenting the initial results, Twin Creeks determined that an upgraded machine and pyramid panels would be a possible solution to meet production needs. The testing of a machine eliminated the risk of capital costs to Newmont and provided Derrick the opportunity to obtain additional data."

Jan 1, 2015

By John W. Lane

Climax Molybdenum Company, a Division of American Metals Climax, Inc., operated a hydrometallurgical plant* at Climax, Colorado from August 1966 through August 1968 to recover molybdenum from a mixed oxide and sulfide ore. The ore treated for this addition to the existing plant contained sufficient Molybdenite values to be mined for Molybdenite recovery alone, so that the oxidized molybdenum recovery could be regarded as a byproduct operation. Climax is located at an elevation of 11,300 feet. All process equipment, except thickeners, was enclosed in buildings. Annual snowfall is approximately 250 inches per year. Paved highways and rail service to the plant are maintained and kept open all year. Most of the employees live in the town of Leadville, which is approximately twelve miles from the plant site. The sulfide flotation plant handles 40,000 to 45,000 tons per day of ore. The mine is one of the world's largest underground mines.

Jan 1, 1971

By Fred L. Myers

The use of finite element programs for evaluating large grinding mill shells is becoming increasingly popular. However, large scale, detailed analysis can become a burdensome task when one is required to manually prepare the necessary data to be entered into the program, while evaluating the voluminous results is even more devastating. Although available computerized finite element analyses can reduce computation time from years to months or even weeks, additional pre and post processors can reduce the time for data preparation and result evaluation to hours, while simultaneously reducing the probability of human error. Examples of the uses of these processors are presented as well as typical modeling techniques.

Jan 1, 1979

By K. Y. Haramy

A scale-invariant theory of the strength and deformability of rock masses in static equilibrium and at incipient failure is proposed. The theory provides a rationale for designing structures in rock. This paper presents results of experiments conducted by the U.S. Bureau of Mines and theoretical methods to determine and interpret in situ strength of rock masses using the borehole shear tester.

Jan 1, 1995

By Liming Yuan, James Rowland, Lihong Zhou, RICK THOMAS, DAVOOD BAHRAMI

Continuous monitoring of carbon monoxide and other fire-related parameters by means of an atmospheric monitoring system (AMS) has been used by the mining industry for early fire detection in underground mines. The National Institute for Occupational Safety and Health (NIOSH) initiated a project to integrate real-time AMS sensor data with NIOSH’s mine fire simulation program, MFIRE 3.0, to simulate and predict the spread of smoke that would provide assistance to mine fire emergency response personnel. Determining the heat release rate of a fire using the monitored sensor data was a critical component of the successful completion of this project. NIOSH researchers developed a direct method to calculate the heat release rate when a fire is within close range of sensors. However, this method is only applicable to the case where a fire occurs in AMS-monitored airways. This paper presents an improved method for determining the fire heat release rate for complicated scenarios where a fire is distant from sensors and airflow splits and merges are present. The method was validated using a fullscale diesel fuel fire test conducted in the Safety Research Coal Mine at the Pittsburgh Mining Research Division and can help mine operators and safety personnel make informed decisions during a fire emergency.

Jul 31, 2020

By Ulrich Maidl, Jamal Rostami, Ulf Gwildis

Tunnel Boring Machines (TBM) have more or less become the preferred method of tunneling in various ground conditions and Programmable Logic Controllers (PLC) or microprocessors are standard features on TBMs to monitor and record various sensory systems on the machine providing the possibility for machine automation and control. The data collected from these sensory systems and channeled through PLC is stored for real-time analysis or use by the operators. Based on typical construction specifications, part of the information collected in the process is shared with the project management team representing the owner. Machine data automatically acquired during TBM advance is typically processed by specialized software to offer the project team data visualization and evaluation options. Interfacing with Geographic Information System (GIS), Computer-Aided Design (CAD), 3-D geologic model, instrumentation data bases, and Document Management Systems (DMS) allows for developing Building Information Models (BIM) of the tunnel’s as-built condition. Application of Artificial Intelligence (AI) processes such as Machine Learning (ML) have already been used for analysis of data, including performance prediction of hard rock TBMs, and exhibited the potential of big data analytics in improving the productivity of the operations. This paper outlines anticipated disruptive technological advances with implications on geotechnical exploration, TBM operation, face condition tracking, subsurface risk allocation, and claims management in the future.

Jun 13, 2021

By Cody Edwards, Ross Webb

5 miles of soft ground tunnel excavation for the SAWS W‑6 project finished months early despite difficult conditions. Success was achieved using TBMs and other equipment built long before most of the crew was even born. The old school means and methods easily adapted to the conditions encountered and were key to the project’s success. Unfortunately, an industry trend is to specify more “advanced” equipment which can sacrifice adaptability or productivity for a perceived reduction in risk. This case history discusses when traditional methods may be the best option.

Dec 1, 2022

By Joern Katzer

It is vitally important to any tunnel project to have an accurate and reliable survey control network inside the tunnel for layouts, as-built surveys, and to provide guidance to the tunnel boring machine (TBM). However, the concepts and methodology to provide such a survey network are sometimes not well understood. For example, the first anticipated survey task that takes place during the bidding process is often ignored, which is to provide a comprehensive survey network preanalysis for the surface network and tunnel traverse based on survey statistics that will be used to make informed decisions on the survey requirements and methodology. Instead, these steps are often only vaguely based on previous results and prior tunneling experience. But each tunnel is different, and a solution that worked for one tunnel project might be unsuitable for another. The purpose of this paper is to provide tunnel project engineers, managers and surveyors with the general concepts for tunnel survey methodologies and examines several statistical tools for a basic horizontal and vertical tunnel survey preanalysis. These survey statistics tools provide useful estimates of the expected lateral and vertical tunnel traverse accuracies, but are not a replacement for a comprehensive tunnel network preanalysis. The proposed formulas do not take centering errors into account, are using average distances for each traverse leg, and assume that the survey data is free of outliers in the measurements. It is very important that the estimated instrument accuracy is based on true values that are reflective of measurement precisions that are actually achievable inside the tunnel to provide accurate results.

Dec 1, 2022

By Mike Wongkaew, Brandon Kluzniak, Per Vilhelmsson

Rail access to Ontario International Airport (ONT) has long been a goal of San Bernardino County Transportation Authority (SBCTA) to increase public transit options to ONT and provide incoming ONT passengers improved access to San Bernardino County and the greater Southern California region. This paper describes the planning for the Design-Build-Operate-Maintain (DBOM) delivery of an emerging technology tunnel connection between the Rancho Cucamonga Metrolink station and ONT. The paper discusses key technical considerations, challenges, and opportunities; conceptual configuration development; and construction planning and establishment of the footprint for the underground connection.

Dec 1, 2022

By P. Schmäh

Nowadays, small diameter tunnels are increasingly considered in pipeline projects as an alternative for sensitive crossings or when soil conditions limit the use of conventional pipeline installation methods like HDD. Safety concerns play a key role, especially for inner-city installations. Pipe jacked microtunnels and small segment lining tunnels can serve as casing tunnels if access is required during construction for the change of cutting tools in challenging ground conditions or for maintenance of the pipeline in operation. Small diameter tunneling solutions offer a high degree of flexibility for alignment design in terms of geology, length and radius.

Jun 13, 2021

By Jafar Safarian, Leiv Kolbeinsen, Stian Seim, Hossein Salehi

The present work aims to investigate the link between the oxidation and reduction of a weathered ilmenite concentrate in terms of phase transitions, microstructural changes, and element distribution. An ilmenite concentrate sample was pelletized and fired at 1000 °C in air, and as a result, the pellets were oxidized. The oxidized pellets were reduced by hydrogen gas at 1000 °C, which yielded almost complete metallization of the iron content of the pellets. The ore and the pellets were characterized in each step by XRD and SEM techniques, and distribution of elements and phases were investigated. Ilmenite, pseudorutile, and rutile were the main phases detected in the ilmenite concentrate sample, and depending on the weathering degree of the particles, different fractions of the phases were identified in their microstructure. It was found that irregular rutile grains dispersed in a pseudobrookite matrix is the morphology of the oxidized ilmenite phase. However, increasing microcracks and porosities were the only microstructural changes in the pseudorutile phase after oxidation in air. Studying the specific types of the ore particles and their oxidized and reduced forms indicated that the phase distribution in the ilmenite ore particles dictates the phase distribution in the oxidized and reduced ones. Results show that the morphology of the reduced particles includes a titanium (III) oxide matrix in which reduced iron globules are dispersed.

Feb 8, 2021

By E. R. Bauer

The trend in underground room-and-pillar coal mining is to employ remote-control continuous mining machines and extended cuts, 12 m (40 ft) deep or more. This system of coal extraction, adopted by over 435 mines, can create additional worker-safety hazards. To address the ground control and worker-positioning hazards, a combination of statistical analyses and numerical modeling was conducted. Initially, the reported roof-fall incidents and fatalities were reviewed to delineate the ground-control hazards. Then, the application of the Coal Mine Roof Rating (CMRR) for estimating safe extended-cut depths was evaluated. Finally, computer modeling to predict roof displacements during extended-cut mining was completed. The paper describes the results of these studies and their impact on the safety of extended-cut mining.

Jan 1, 1999

By J. K. Grunig

A process consisting of leach, continuous countercurrent decantation, resin-in-column ion exchange, evaporative crystallization of beryllium sulfate, and decomposition of the sulfate was developed for Spor Mountain, Utah, ores. The process is metallurgically sound, has a minimum of process steps, and is applicable to a wide variety of beryllium ores. The most novel aspect of the process is a resin system of ion exchange which is highly selective for beryllium and which rejects substantially all impurities except for minor amounts of aluminum, magnesium, fluorine, and sulfate in addition to beryllium. The oxide from sulfate decomposition meets specifications of potential users.

Jan 1, 1982