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By Robinson Leon-Diaz, Alberto Jaen-Toribio, Raymond Blanchard, Mike Deevy, Miguel Fuentes-Llanos

"Tunnels designed to NFPA 502 are required to withstand the RWS time-temperature curve, more specifically prevent progressive spalling and loss of strength of steel reinforcement. Fire boards or spray-on layers can be effective, however, these solutions have capital and whole-life cost implications. The use of “fire resistant” concrete based on a suitable aggregate with polypropylene fibers has also increased in recent years. This article presents a new methodology for thermal and structural analysis of segmentally lined tunnels, which permits the analysis of project specific fire curves and an assessment of different fire protection strategies. The effectiveness of fire boards is assessed along with whether “fire resistant” concrete alone is a viable means of achieving the required protection. Finally, since NFPA 502 recommends water-based fixed fire-fighting systems for Category C and D tunnels, we discuss the question of how a fixed fire-fighting system should be addressed within the structural design. INTRODUCTION Protecting road tunnels from structural damage and collapse is a key requirement for both life safety and business continuity. Where road tunnels are part of key highway corridors, protecting business continuity is a high priority for owners, operators and the Authority Having Jurisdiction. For existing tunnels, compliance with NFPA 502 may require upgrades with either passive fire protection and/or water-based fixed firefighting systems. For new tunnels, compliance with NFPA 502 requires a combination of good practice in design and fire testing. A water-based fixed firefighting system is a Conditionally Mandatory Requirement1 for Class C and D tunnels, i.e. all tunnels greater than 300m and 1000m long respectively. The basis for fire safety design of new tunnels and assessment of existing tunnels is the worst-case fire scenario. A number of factors, including but not limited to the following, influence this design fire scenario:"

Jan 1, 2016

By Sergio Estebanez, Martha Gross, Ruben Rubal, Yvonnick Rescamps, Alexandre Cochennec

The Hampton Roads Bridge-Tunnel (HRBT) Expansion project in coastal Virginia, USA will add two 1.5-mile (2.4 km) TBM bored tunnels alongside two existing immersed-tube tunnels between artificial islands. The site’s unusual constraints and the requirements of a large-diameter variable-density TBM shaped the design-builder’s decisions for handling TBM inputs and outputs, siting the TBM plant and supporting equipment, and sequencing tunnel-construction operations. This paper addresses the logistics necessary to enable key functions of the 46-ft (14-m) TBM and its ancillary equipment, including transport of most materials by barge, U-turn of the TBM on an artificial island, and delivery of materials for the second tunnel through the first one while interior structures are under construction.

Jun 13, 2021

By L. M. English

When plotted as head vs. volume, fan curves start high and decrease in head with increasing volume while mine head curves start low and rise with increasing volume. Their intersection is the system operating point But wait a minute: Isn't head loss a negative number, a debit? And isn't fan head an energy addition, a credit? This, as every ventilation instructor knows, is often a stumbling block to student or audience comprehension. It is possible to use the intuitively correct curves -pressure losses as negative values and energy additions as positive values -and still obtain the correct operating point: adding the two curves produces a third curve that intersects the x-axis at the operating point, the point at \\tIich the fan energy input exactly matches air circulation energy loss. Using this technique also makes it easier to account for outside influences on the system, such as natural ventilating pressure; with the standard approach it is quite easy to add or subtract such influences to the wrong curve. This approach can be extended to the graphical solution of any series/parallel circuit or ventilation net\wrk. The results are the same, and the approach is logically consistent and less confusing.

Jan 1, 1997

By J. R. Patts, J. P. Rider, J. A. Organiscak, A. B. Cecala

"NIOSH recently completed a 15-month study at an underground limestone mine crusher booth which evaluated three research parameters: (1) the effectiveness of a single-filter filtration and pressurization system for improving the air quality inside the operator booth, (2) comparing the effectiveness of ? > 99 and ? > 95 experimental prototype filters in the system, and (3) evaluating the use of three different pressure monitoring devices to determine the performance of the filtration and pressurization system over time. The protection factor was quantified monthly using particle counters in the respirable dust range (0.3–10 µm), and gravimetric dust samples were gathered at the beginning and end of the overall study. Under static conditions and after outlier removal, the single-filter filtration unit installed offered a protection factor between 8 and 216, depending on the filter type and loading condition. The particle counting analysis shows that the ? > 95 filter offers a protection factor greater than 4-times that of the ? > 99 filter when evaluated over 60 minutes. The booth pressure monitors provided data that proved to be a valid indicator of system performance over time. INTRODUCTION Designed and installed correctly, enclosed cabs, operator booths and control rooms offer mine workers protection from physical hazards, such as flying rock, debris, and noise, as well as a more comfortable environment in regards to temperature and humidity [1]. But while it may be easier to quantify whether the A/C unit is working (measuring the temperature) or observe whether the cab offers protection from flying debris, it can be somewhat more difficult to quantify its performance in reducing respirable dust hazards. For over 15 years, NIOSH has been conducting applied research to improve the air quality inside of enclosed cabs of mobile equipment [2-5]. This work has led to the identification and mathematical modeling of enclosed cab filtration systems [6]. The same principles that govern the performance of filtration systems on mobile equipment are applicable to stationary enclosures such as operator booths and control rooms [1, 7]. Stationary enclosures are similar to enclosed cabs; however, the volume of the work area can be significantly larger. In addition, workers who perform their duties in stationary enclosures tend to stay within the room for a greater percentage of the day, as opposed to workers on mobile equipment who may enter and exit frequently. Structural integrity can be easier to maintain as well, as there is typically less vibration and stress placed on these compartments as compared to mobile equipment. In addition to offering protection from dust and flying debris, enclosures must ensure that workers have a healthy supply of fresh air to avoid elevated levels of CO2, which are known to cause headache and dizziness, impairing cognitive function. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) states that enclosures should have no more than 1,100 ppm of CO2 when outside levels are 400 ppm [8]. In addition, the American Society of Agricultural and Biological Engineering (ASABE) recommends a minimum airflow for enclosed cabs of at least 42.5 m3/hr (25.0 cfm) per person [9] to ensure an acceptable level of CO2."

Jan 1, 2017

By J. V. Bymark

It is the intent of this paper to discuss the autogenous grinding circuit at Hibbing Taconite. The scope of the presentation includes; a brief history, the process flowsheet and the steps taken to improve mill productivity, availability and metallurgical performance. Hibbing Taconite is located near the center of the Mesabi Range in Northern Minnesota 100 miles from the Canadian border and 80 miles north of the Lake Superior Port Cities of Duluth and Superior. A 105 mile railroad connects us with the port of Superior, Wisconsin, where our pellets are loaded into lake carriers for lower lake destinations. It is worthy to mention the Mesabi Range's most famous landmark which is immediately to the south of our mine area. This is the Hull Rust Mahoning Mine which operated until the mid-1970's producing more than 700 million tons of red ore between 1893 and 1973.

Jan 1, 1985

By W. S. Fyfe

Gold is mobilized or made soluble under all crustal conditions given appropriate fluid chemistry with molecules which complex gold. In the surface environment chloride, thiosulphate and a host of organics may mobilize gold. In the epithermal range bisulphide appears effective as shown by the classic studies in the Taupo volcanic zone of New Zealand. In the high grade metamorphic to igneous ranges little is know but it appears that gas molecules in the system CO2 -CO-H20-S-C1 can do the job. Precipitation may occur by changes in P-T-EL-pH or boiling where such changes influence the liquid concentration. Of the known regimes information is good for epithermal systems, poor for surface lateritic environments, inadequate for high-T systems. Gold is often concentrated in bio-systems both living and dead. The influence of biosystems is little appreciated. There is a great potential for the discovery of new types of gold deposits and in particular, gold in weathering environments, gold in very high-T environments, gold in strike-slip faults and thrust regimes, and gold as a by-product in materials like coal and other organic debris. By the year 2500 we may find our noble metal resources in the asteroids.

Jan 1, 1987

By H. Maleki

Interwest Mining Company has been collecting geologic data within the last decade in preparation for underground mining of extensive coal reserves in its Bridger Coal property in southwestern Wyoming. During a preliminary data collection program in 2000, Interwest Mining completed geologic investigations, including surface mapping, drilling, aerial photography, rock testing, and limited groundwater investigations. Core from 12 exploration boreholes in the area of interest was tested to determine the mechanical properties of the coal seam and the immediate roof and floor for evaluation of the feasibility of underground mining. Geologic investigations identified the presence of one 7-to-17-ft-thick coal seam throughout the reserve under 1400 ft of cover. During a geotechnical feasibility study in 2002, the authors reviewed available data while completing comparative analyses identifying critical deficiencies in these data. The study projected moderate-to-difficult mining conditions, considering the weak nature of near-seam strata and depth of cover, and thus recommended limiting the longwall reserves to an overburden depth of less than 900 ft. These shallow remaining reserves were located at depths within regional mining experience to justify longwall mining methods. Based on a critical examination of available data, Bridger proceeded with more detailed data collection to improve understanding of the depositional and structural setting of the reserve, hydrogeologic conditions, overburden strength, and premining stress conditions. Additional data was collected during 2003 and 2004 field programs. Since 2003, Bridger has had the opportunity to observe ground behavior in a series of up to 1200-1600-ft- long rectangular openings created during highwall mining. These narrow unsupported openings remained stable in the short term in large areas but the overburden subsided locally in the long-term depending on geologic and panel layout designs. These localized subsidence events allowed an examination of in-situ coal strength based on back analyses of stress. The unextracted highwall areas near Ramp 17 provided an ideal location to access the underground reserves using a 6-entry set of mains. The existing north-south oriented longwall layout for the Bridger Coal was selected by Bridger to maximize resource recovery from the D41 reserves while considering operational and geotechnical constraints. At 45-degrees deviation from preexisting joints and mild horizontal stress field, this orientation was considered beneficial for overall stability while using both sets of joints for facilitating the caving process. The present layout utilizes pillars on 80- to 90- by 200-ft centers, 17-ft entry spans and 750-ft wide longwall panels (Figure 1). Gate pillars are on wide spacings and are intended to act as abutment-abutment pillars to limit strata deformation over the gateroads during longwall mining.

Jan 1, 2008

By Michael Li, Kathryn Rogers, Arie Moerman, Mike Cooper

The Brunswick Mine, a Division of Noranda Inc., produces zinc, lead, copper, and bulk lead-zinc concentrates through underground mining of a large massive sulphide deposit. The mining method employed is longhole open stoping with delayed backfilling. In 1996 Brunswick began a review of its mining methods and backfilling operations. In 1997 the decision was made to convert the backfill system from cemented and uncemented rockfill to paste backfill prepared from mill tailings. This paper will describe the features of the backfill preparation and distribution systems, review the handling of technical issues, and discuss experiences since plant commissioning.

Jan 1, 2001

By M. G. Mudrey

Considerable potential for metallic mineral resources in the lower Proterozoic rock of the Lake Superior region exists (Mudrey and Kalliokoski, in press). Most of the identified resources occur within a 2.0- to 1.9-b.y.-old lithotectonic assemblage characterized by extensive sedimentary strata in the north and thick volcanic se- quences in the south, all deposited on a two-terrane, composite basement of Archean age (DeMattis, 1989). Since the late 1960s, measured resources of nearly 90 Mt (100 million st) of typical volcanogenic massive sulfide at eight localities in Wisconsin have been discovered. The largest of these, near Crandon, contains about 61 Mt (67 million st) of ore averaging 5.6% zinc, 1.1 % copper, and 0.5% lead. Although none of these properties are in production, estimates by Mudrey (1978) suggest that Wisconsin could become a major contributor of newly mined zinc and copper in the United States. These discoveries and uranium and gold discoveries in the Canadian Precambrian are what have led to in- creased metallic mineral exploration throughout the northern half of Wisconsin (Fig. 1). In this chapter, we discuss the geology and legal framework in which the Proterozoic volcanogenic massive sulfide deposits were found. Exploration activities for other metals have generally been negative, and have been background noise for the legislative activities related to the massive sulfide discoveries. Uranium exploration has been consistently negative, although several different environments have been assessed. Other metal discoveries. such as titanium/vanadium, have been subeconomic.

Jan 1, 1991

By Jan M. Andersson

This paper will discuss the background information about rock cutting tools used for soft ground excavation, their history and evolution. A brief review of the current state of the art manufacturing technology will be presented and some parameters related to the material used in the drag and conical type pick cutters and their impact on their life and performance will be explained In addition, the selection procedures for choosing the right bit for excavation of a particular geological formation will be reviewed A set of guidelines will be provided for initial selection of the tools for various machines and rock formations. The methods for estimation of the tool life in various materials and the influencing parameters along with limitations of the rock cutting tools will be discussed as well.

Jan 1, 1998

By T. R. Raponi, D. Barnes

The Williams Mine mines and mills 6000 t/d (6600 stp’d) of gold ore using SAG/ball milling, leaching and CIP, electrowinning and refining. Electrowinning, high-pressure cathode washing, filtering, retorting and refining are based around the use of knitted stainless steel mesh cathodes. Their primary advantage over conventional steel wool cathodes is that electrowon gold can be washed off and the cathode can then be reused. Typically, the knitted cathodes have a useful life of up to 15 months. Gold production of up to15 t/month (50,000 oz/month) is easily processed with this system. Presented is a description of this operation, including a review of the equipment and performance data.

Jan 1, 1992

By Peter N. Yanker

The two types of dryers used in the drying of copper concentrates are the rotary dryer and the spray dryer. The rotary dryer has until recent history been the traditional drying method used, Although spray dryers have been used in the chemical field for many years it is only recently that they have been accepted for drying of copper concentrates. The comparison made here will apply in a narrower sense to the drying of copper concentrates as fed into the reverbatory furnaces of the Smelter. To compare a rotary dryer and a spray dryer, which are two totally different methods and pieces of equipment, it is best to view them as systems each made up of certain elements

Jan 1, 1976

By W. E. Lamont

As part of its program to minimize mineral and metal needs, the Federal Bureau of Mines conducted investigations to determine the feasibility of producing foundry-sand-grade olivine concentrates from low-grade sources. Using a Bureau-patented attrition-grinding technique, concentrates meeting Steel Founder's Society of America (SFSA) specifications for loss on ignition (LOI) were prepared. Studies showed that green strengths and tensile strengths of the attrition-ground olivine were equivalent or superior to those of commercial materials. Metal-casting studies showed that molds of attrition-ground olivine produced better surface finishes. The improved surface finishes were attributed in part to increased grain sphericity.

Jan 1, 1977

By G. Bylapudi, A. Spearing, J. Weber, K. Mondal

U.S. National Institute for Occupational Safety and Health (NIOSH) reports state that about 100 million rock anchors are installed annually in U.S. coal mines (Tadolini et al., 2006), and rock-related safety remains an issue. The majority of these coal mines have conditions that make corrosion probable in the longer term. Despite this, very little research has been performed to analyze corrosion and its effects on rock anchors in coal mines. To further evaluate the effects of corrosive conditions in coal mines on rock anchors, three different experiments were conducted during an initial Illinois Clean Coal Institute (ICCI)-funded project from 2008-2009. The results of these experiments were further studied, with additional tests, in the extended ICCI-funded project during 2011-2012. The experiments were destructive testing, electrochemical testing (potentiodynamic polarization tests) and open circuit potential (OCP) testing, conducted in order to study corrosion in environments similar to those found in Illinois coal mines with a focus on major rock anchor types typically installed underground. Destructive test results showed highest reduction in peak strength at higher pH and temperature. From the destructive test results, epoxy-coated and galvanized anchors were observed to be better when compared to uncoated. Electrochemical testing was performed to find the corrosion potential and corrosion rates of ASTM A615 steel grades 40, 60 and 75 in four different solutions of varying sulfur content at ambient temperature. The effect of temperature and pH levels on corrosion potential and corrosion rates of steel grades were also evaluated with additional electrochemical testing, where an increase in temperature with all other constant conditions caused a significant increase in the corrosion penetration rate. OCP data indicated higher corrosion potential values (-mV) for rock anchors in wet areas, when compared to those from the dry areas. OCP test results of the rock anchors from the laboratory corrosion chambers were similar to those measured in the sampled coal mines.

Jan 1, 2013

By J. Lovering, H. Wilhelm, P. Siewert

Introduction The Afton property is located 290 km (180 miles) by air east-northeast from Vancouver and 14 km (8.7 miles) west of Kamloops, a city of 60,000 people, in south central British Columbia, Canada. The mine is adjacent to the Trans-Canada Highway at an elevation of 670 m (2198 ft) above sea level. The ore body is a porphyry copper deposit that has undergone supergene alteration. The major economic minerals in the supergene zone are native copper and chalcocite with chalcopyrite and bornite in the hypergene areas. The grade is 1% with an overall copper distribution - 70% native, 25% chalcocite, and 5% chalcopyrite with bornite and covellite. The ore also contains important but variable amounts of gold and silver. The mill was designed to treat 6350 t/d (7000 stpd). Semiautogenous grinding was selected to minimize capital cost and because of the expected high clay content of the ore, which would have caused problems in a conventional crushing and screening plant. Test work indicated that a recovery of 87% was possible in a circuit incorporating both flotation and gravity separation. Flowsheet Run-of-mine ore is crushed in a 1.06 x 1.65-m (3.5 x 5.4-ft) Allis Chalmers gyratory crusher set at 228.6 mm (9 in.), closed side setting. The surge pocket, below the crusher, is emptied by a Hydrastroke feeder onto number one conveyor, which discharges onto a 180,000-t (198,416-st) coarse ore stockpile. Six Hydrastroke feeders on two conveyors withdraw the crushed material from the bottom of the pile. These two conveyors, in turn, discharge onto the belt feeding the semiautogenous mill. The live storage in the stockpile is approximately 22,000 t (24,250 st), sufficient for three days' mill feed. Primary grinding is accomplished in an 8.5-m (28-ft) diam by 3.7-m (12-ft) long Koppers (Hardinge Cascade) mill (Fig. 1) containing a 10% ball charge and driven by a 4000-kW dc variable speed motor. The mill dis¬charge is pumped by a 10 x 12 G.I.W. pump to a 1.22 x 4.88-m (4 x 16-ft) stationary screen sloped at 20°. Screen oversize returns to the semiautogenous mill (SAM), and the undersize flows by gravity to the ball mill discharge pump box. Secondary grinding is performed in a 5-m (16.4-ft) diam by 8.84-m (29-ft) Koppers overflow ball mill driven by a 3430-kW synchronous motor through an air clutch. The mill is in closed circuit with a Krebs Cyclopac containing 10 635-mm (25-in.) cyclones and the cyclone overflow, at 35% solids and 65% to 70% -200 mesh, is flotation feed. In order to limit the buildup of native copper, circulating in the secondary grinding circuit, a portion of the underflow from the cyclones is processed in a circuit containing screens, cyclones, and shaking tables to produce a finished metallic copper concentrate. Primary mill variable speed drive The overall waste to ore ratio at Afton was 4.5:1. The mining was to be done with only three shovels, which meant that it was highly unlikely that more than one of them would be in ore at any one time. The resulting inability to blend the mill feed made it impossible to prevent wide swings in the grade and grindability. The variable speed do drive motor installed on the semiautogenous mill was selected because of the extreme variability of the Afton ore body. This variability has persisted throughout the lifetime of the mine. There are times, however, when due to ore conditions, the mill is operated at full speed (78% of critical) for extended periods of several shifts duration. There are other times when the mill speed may be changed several times in a 12-hour shift due to changing ore conditions. When ore is processed that contains a fairly large proportion of fine native copper, the primary mill speed and, consequently, the tonnage may be reduced to improve the secondary grind and to maintain an acceptable grind and recovery. High clay ores require less mill speed and more dilute grinding densities. In the latter case, the slower primary mill speed also helps to minimize damage to the mill liners. Approximately 57% of the time the mill operates between 90% and 100% of full speed or between 71% and 78% of critical. The variable speed is also used for inching during mill relines.

Jan 1, 1987

By Stuart Ratcliffe, Denis Kidby

The development of Vitrokele™ Technology over the last 10 years is reviewed with reference to mine site piloting and com­mercial applications. The first mine site piloting was conducted in Australia in 1989 followed by a further six continuous site trials in Australia, Canada and the USA. These major pilot plant studies are complemented by over 50 laboratory scale batch and pilot testwork programmes. The first commercial plant using Vitrokele™ Technology was the Connemara project commissioned in Zimbabwe in 1995. Subsequent to this, three commercial scale projects have been designed using Vitrokele™ to recover precious metals, base met­als and cyanide. The various projects are discussed with relation to the differ­ing flowsheets applied to each particular case.

Jan 1, 1998

By Leonidio Stegmiller

Since the petroleum crisis in 1973, charcoal1 is being considered one of the most important fuel for the Brazilian consumers, mainly for pellet's producers. In replacing fuel by charcoal mixed up with ore, obviously one of the first thing to be investigated is its influence in the product's quality. Special attention has been given to the metallurgical characteristics. This paper infocus the effect of increasing dosings of charcoal to the pellet's porosity and how other physical and metallurgical characteristics will be affected accordingly. This work was carried out using two different finesses of charcoal and dosing varied from 0.5 to 2.0%.

Jan 1, 1982

By Leonard Bronitsky

The construction mineral aggregates industry--the largest industry on a tonnage basis--is threatened with large shortages in the near future. Ironically, these common minerals which include sand, gravel, and stone are among the most plentiful in the earth's crust. However, as these minerals are low in value and used in large volumes, they are extremely sensitive to transport cost, e.g., a haul of 20 miles doubled the delivered cost of mineral aggregates. Consequently, these minerals must be located close to points of demand to have economic usefulness. But the development of new deposits is virtually impossible near many urban areas for legal, sociological and economic reasons. The spector of unfinished urban transport systems, curtailed residential construction, and a general deterioration of the physical urban plant, looms as a direct consequent of future mineral aggregate shortages in the U. S. metropolitan areas. The shortages of mineral aggregates in the Greater New York Metropolitan Area (G.N.Y.M.A.) are prototypical of the shortages faced by the U. S. Metropolitan areas. This paper presents an economic analysis of the consequences of not considering the broad aspects of conservation economics as a major component of resource management. The needless annual cost for the G.N.Y.M.A. is shown to be $30 million.

Jan 1, 1974

By P. M. Soupios

An integrated suite of environmental methods was used to characterize the hydrogeological, geological and tectonic regimes of the study area, to determine the geometry of the landfill (depth and spatial extent of electrically conductive anomalies), to define the anisotropy caused by bedrock fabric fractures and to locate potential zones of electrically conductive contamination. The study area which covers an area of about 0.08 Km2 is a municipal solid waste site (MSW), located 20Km West of Herakleion in the central part of Crete (S. Greece). The landfill is located in a northwest oriented valley with highlands to the northeast and southwest. The combination of geophysical methods and chemical analysis are commonly implemented for characterization and management of land-fills. At the particular site, geophysical methods were focused on studying the electrical insolating properties of the materials, electrical con-ducting properties of fluids (leachates) and electromagnetic properties of the disturbed regolith materials in the burial zones. Three different types of geophysical surveys were performed: 1) 2D electrical tomography (ERT), 2) electro-magnetic measurements using very low frequencies (VLF) and 3) electromagnetic conductivity (EM31). Furthermore, in order to calibrate the geophysical methods dielectric spectrometry measurements are conducted. To evaluate the environmental degradation of the area, soil and liquids samples were collected.

Jan 1, 2005

By Per-Martin Sandgren

LKAB's ores have specific mineralogical properties that make them especially suitable for the production of super-grade concentrates. Conditions are particularly good for this purpose at Malmberget, where a concentrate for high-purity sponge iron production has been produced for many years. Until 1978 the approximate assay was 71.2 % Fe and 0.45 % SiO2. Since then the assays have been improved by process modifications to approximately 71.5 % Fe and 0.20 % SiO2. Scope exists for still further improvement. In recent years the production of fractioned concentrates has been started. The material lies within the size range 74-125 µm and the approximate chemical analysis is 71.6 % Fe and 0.30 % SiO2. Other special products are under discussion. The Malmberget ores are also suitable for the production of high-purity direct reduction pellets with a SiO2 content below 1 %.

Jan 1, 1981