Search Documents

By T. B. Linde

The Morenci In-pit Crusher and Conveyor System has been designed with safe production and cost savings in mind. Large open pit mines around the world have been installing semi-mobile crushers and linking them with a pit conveyor system to lower unit cost. At Morenci two 60/89 in. gyratory crushers are incorporated into the semi-mobile crushing plants. The ore is reduced to -8 in. and transported out of the mine on a 60 in. steel cable belt. This paper includes an overview of the Morenci In-pit Crusher and Conveyor System from the drawing board to open pit installation and finally a discussion on operating and repair considerations.

Jan 1, 1990

By S. Koro

The current economic climate of low commodity prices and increasing costs has put a lot of pressure on mining companies to ensure their operations will survive through the current economic downturn. While history tells us that the cycle will turn around and prices will go back up again, how many mining companies will be left to take advantage of the next upturn? On average in Australia, the maintenance of mining equipment accounts for up to 50% of operating costs; which equates to nearly $15bn per year. In addition to trying to boost productivity, mining companies are also putting a lot of pressure on reducing costs; all with the intention of maintaining/increasing profit margins and thereby keeping shareholders ?happy?. The whole premise of our economy is based on ?growth? and ?profits?. Movements in the market place force mine owners to ?react? to short term fluctuations. And if that movement is downward; operations people at the sites are forced to start reducing costs. Is this cost reduction done in a logical, systematic way where all risks (short-, medium- and long term) are considered? Invariably, the answer is no! Short term ?fixes? are normally implemented with little, or no, regard for medium- and long-term impact. And the reason for this is that management is not fully focused on the long term; focus is mainly on survival. Decision making is driven by shareholder sentiment and history tells us that this is largely short-term. So given these paramteres to work within, what role can ?Asset Management? play in assisting management to meet shareholder and market requirements whilst still maintaining long-term viability of their operations (to the long-term benefit of shareholders dare I say). As maintenance costs account for nearly half the operating costs of mining companies; the ?smart? management of assets is not only crucial; it is essential for survival in today?s economic climate. What is asset management? Asset Management, according to the UK-based Institute of Asset Management (IAM) is ?the systematic and coordinated activities and practices through which an organization optimally and sustainably manages its assets and asset systems, their associated performance, risks and expenditures over their life cycles for the purpose of achieving its organizational strategic plan.? How important is asset management in today?s mining companies? IAM goes on to say: ?This definition of asset management represents a significantly greater scope than just the maintenance or care of physical assets, and is closer to the central purpose of an organization. Good asset management considers and optimizes the conflicting priorities of asset utilization and asset care, of short-term performance opportunities and long-term sustainability, and between capital investments and subsequent operating costs, risks and performance. ?Life cycle? asset management is also more than simply the consideration of capital costs and operating costs over pre-determined asset ?life? assumptions. Truly optimized, whole life asset management includes risk exposures and performance attributes, and considers the asset?s economic life as the result of an optimization process (depending upon the design, utilization, maintenance, obsolescence and other factors).?

Feb 23, 2014

By F. L. Bazzanella

Cyprus Pima has two concentrators, one with a conventional crushing-grinding circuit and the other using semi-autogenous grinding followed by ball mills.

Jan 1, 1978

By H. R. Bullis

Lupin is located on the shores of Contwoyto Lake at lat. 65° 48'N, Long. 111° 15'W and lies about 80 kilometers south of the Arctic Circle. Since start up in 1982 the mine has produced over 2.15 million ounces of gold from 6.66 million tonnes of ore grading 10.63 gm/tonne. Total remaining reserves at 1993 year end were 5.1 million tonnes at a grade of 9.11 gm/tonne (1.65 million ounces). This is sufficient for 7 -8 years at the present annual production rate of about 200,000 ounces. The Centre and West Zones of the deposit are open to depth. The deposit is in an Archean metaturbidite sequence of the Contwoyto Formation, which has been mapped as part of the Yellowknife Supergroup of supracrustal metasedimentary and metavolcanic rocks making up part of the Slave Geologic Province. These rocks have been subjected to regionar and contact metamorphism and to several phases of deformation. Six stages of Archean plutonism have been identified and all Archean rocks have been cut by Proterozoic diabase dyke swarms. Gold mineralization in the Lupin deposit is commonly fine grained and associated with pyrrhotite and arsenopyrite in amphibolitic banded iron formation. The gold-bearing portions of the host iron formations are characterized by the presence of multiple quartz veins and the pervasive replacement of grunerite by hornblende. In sparsely mineralized portions of the host iron formation, zoning of sulfides about quartz veins is clearly seen with the arsenopyrite halo being more restricted around the veins than the pyrrhotite halo. In well mineralized portions, quartz vein densities approach one vein per metre along strike. In these areas pyrrhotite distribution in the iron formation is more pervasive and the rock takes on the appearance of a banded sulphide rock.

Jan 1, 1995

By T. J. Batchler

"INTRODUCTION A variety of standing supports are being applied in underground coal mining operations to assist in providing stable mine entries. Standing support performance requirements depend on the nature of the ground deformation behavior, and therefore require a good understanding of the interaction between the support and ground to achieve an optimum roof support system. Mining operations often employ standing support strategies that are unique to their mine. A support system that functions successfully in one situation could fail in another situation. It is important that the design and installation of the standing support systems provide the highest probability of preventing roof falls. Considerable research and development has been conducted by support manufacturers to develop standing support technologies for the mining industry. The National Institute for Occupational Safety and Health (NIOSH) researchers, with the cooperation of various support manufacturers, have developed a testing protocol that evaluates performance characteristics of these standing support systems.. Using this protocol, each of these support systems has gone through rigorous safety performance testing under controlled loading conditions in NIOSH’s Mine Roof Simulator (MRS). It is important to understand the unique performance characteristics of each type of standing support. This information allows mine operators to determine if the support system is compatible with the conditions in the mine and to compare each support system and determine if that support will provide equivalent or improved support capability. This paper provides a comprehensive summary of support performance to facilitate this objective. SUPPORT DESIGN CRITERIA AND THE GROUND REACTION CURVE Standing roof support systems are designed to prevent unplanned roof falls. The selection of the standing support is based on the interaction of the support with the surrounding rock mass, and its function is to assist the primary support system in maintaining the integrity of the immediate roof. The standing support works to control the immediate roof structure by resisting deformation that contribute to delamination of the bedded layers and displacements that lead to separation of the bolted zone from stable roof structures above the bolted horizon (Barczak, 2005). Standing supports should be installed early enough and develop sufficient capacity to bring deformation of the ground into equilibrium before a critical deformation is reached that leads to a detached block condition, at which point the standing support will be required to carry the entire dead weight of the detached rock mass to prevent a roof fall from occurring (Mucho, 1999). The ground reaction curve (GRC) can be used to assist in determining the compatibility and design requirements for a support system. It is important to understand the significance of the ground reaction relative to the support design requirements. The ultimate objective is to match the support behavior to the ground response and create equilibrium (stability) of the rock mass. This equilibrium is accomplished when the support loading intersects the ground reaction curve (Figure 1). Essentially, the ground reaction concept implies that the convergence in the mine entry is controlled by the magnitude of the support resistance. However, as a passive support, the standing support develops its loading through convergence. As such, the support needs to maintain its load capacity through the associated deformation of the ground and resulting entry convergence until the equilibrium condition is reached. This requirement causes factors such as the support stiffness, peak capacity, yielding characteristics, and stability to be fundamental to proper support design and application. NIOSH contributes to providing this understanding through full-scale performance testing of support products in the Mine Roof Simulator."

Jan 1, 2017

By L. Yan, T. Lutz, J. Noll

"Mine disasters, such as fires and explosions, can create a hazardous atmosphere due to the generation of carbon monoxide (CO). After a mine disaster, contaminated mine air can enter the refuge alternative (RA) as miners enter. Most built-in-place (BIP) RAs use an air delivery system to provide an unlimited supply of breathable air through a borehole which also serves to purge contaminants. In order to determine what levels of contaminants enter the RA, researchers from the National Institute for Occupational Safety and Health (NIOSH) conducted testing in NIOSH’s Pittsburgh Experimental Mine using groups of 5, 15, and 30 subjects entering the RA. The experiment used sulfur hexafluoride (SF6) as a tracer gas that was released into the air outside of the BIP RA to establish a uniform concentration. After the human subjects entered the BIP RA, the SF6 levels inside the RA were measured to quantify how much of the tracer gas entered the BIP RA. In tests conducted while the borehole air supply was left off as test subjects entered, interior contaminant levels were less than 3% of the exterior concentration. In tests conducted with the borehole air supply activated as test subjects entered, the interior contaminant levels were measured at less than 2% of the exterior concentration. Considering a mine disaster can result in 10,000 ppm of CO in the mine atmosphere, these percentages indicate that unhealthy CO concentrations that may lead to headaches, dizziness, and loss of judgement can occur in a BIP RA. This information will help mines make decisions concerning air locks, air delivery systems and a determination if purging mechanisms are necessary. INTRODUCTION The Mine Improvement and New Emergency Response Act of 2006 (MINER Act) was enacted in the wake of three mine explosions/fires that claimed 19 lives that year. Intended to help improve underground coal mine accident preparedness, the MINER Act includes provisions that target mine safety issues in areas such as emergency response planning, adoption of new technology, training and education, and enforcement of mine safety standards (MSHA, 2006). Section 13 of the MINER Act specifically directs the National Institute for Occupational Safety and Health (NIOSH) to provide for research into the effectiveness and viability of RAs for underground coal mines. This mandate culminated in the 2009 adoption of changes to the 30 CFR mining health and safety regulations, requiring underground coal mines to provide RAs capable of maintaining a life-sustaining environment for persons trapped underground. Such RAs can be either pre-fabricated or BIP shelters. The regulatory changes also include provisions establishing requirements for Mine Safety and Health Administration (MSHA) approval of RAs and their components, and among these provisions are numerous criteria for providing a safe, breathable atmosphere within RAs."

Jan 1, 2018

By James D. Cooper

Technologic advances in materials utilization during the past two decades have brought is a long way toward the point where we can make the products we need from the materials we have readily available. Notable examples are the synthesis of diamond, zeolites, quartz crystal, mullite, and mica, and the development of phosphate bonded tale. Two of these--zeolites and mullite--involve the use of clays. There is little reason to doubt that equally important advances will be realized in the next decade, and that clays will play an important role in the developing materials technology. Indeed, the stage is already set for many of them. This discussion is concerned primarily with the high quality, relatively high priced clays, kaolin, bentonite, fuller's earth and ball clay. The first three have enjoyed demand growth rates over the past two decades which on the average exceeded the growth rate for the economy as a whole. There are indications that demand for ball clay will be growing at a faster rate in the future.

Jan 1, 1970

By D. Burkhard, E. Herth

"Geologic structure and properties are the primary influences on ground control at San Juan Mine. Geotechnical properties of the coal seam and near seam strata, the presence of above seam sandstone paleochannels and water, are thought to be the leading contributors to ground control issues. It is the confluence of specific geologic conditions rather than isolated features that most often produce adverse conditions. Altering primary support installation and mining practices are done when unfavorable conditions appear during development. Installation of standing support is most often employed when adverse conditions develop at later dates. REGIONAL GEOLOGIC SETTING San Juan Mine is an underground coal mine located on the western flank of the San Juan Basin in northwest New Mexico. The San Juan Basin is contained within the south eastern region of the Colorado Plateau geographic province. The basin contains multiple coal bearing formations and is also a major producer of coalbed methane gas. San Juan Mine is stratigraphically located within the Fruitland Formation. From a prominent monocline marking the western boundary of the basin, the formation dips gently to the east towards the center of the basin. The primary driver for the deposition of coal bearing formations within the basin was the Cretaceous Inland Seaway. Multiple cycles of transgression and regression driven by sea level rise and tectonic subsidence deposited rock types from marine shale’s to terrestrial sandstones. The Sevier Mountains to the west of the seaway likely provided the sediment supply for the Fruitland Formation. During a major cycle of seaward regression, the Pictured Cliffs Sandstone Formation prograded over the marine Lewis Shale. The coal bearing Fruitland Formation followed, being deposited over the Pictured Cliffs. The Fruitland Formation contains numerous coal seams and is approximately 400 ft. thick at San Juan Mine. Fruitland Formation coal seams are numbered in order of superposition. San Juan mines the Fruitland number 8 seam. Dating has placed the age of the seam at approximately 73 to 75 million years [1]. LOCAL GEOLOGIC SETTING The Fruitland 8 coal seam dips approximately 1-3 degrees towards the E-NE. At San Juan Mine, the seam displays a mild plunging, synclinal structure, the axis roughly bisecting the mine from west to east. The number 8 seam consists of five coal benches and four volcanic ash band partings labeled sequentially based on superposition. The lowest portion of the seam is the 8-1 bench, the 8-2 through 8-5 benches following sequentially to the top of the minable seam. Ash band partings are labelled P1 through P4 from bottom to top respectively. The presence of distinctive partings and benches allows for seam definition and aids in identifying mining horizons."

Jan 1, 2016

By A. Ang-Ug, L. Gurieff

"The Phu Kham Cu-Au mine in Laos is owned and operated by Phu Bia Mining Limited. The deposit is a complex and low grade Cu-Au porphyry ore. The rougher feed has a particle size distribution of 80% passing 110 µm, and the rougher concentrate is reground for cleaning to 80% passing 25 µm. The Cu losses in the cleaning circuit are primarily in the <12 µm fraction. A randomised paired ON-OFF test of magnetic conditioning in one of the two parallel cleaner 1 circuits was undertaken. The results showed that with magnetic conditioning there was approximately a 10% reduction in the <12 µm Cu distribution in the cleaner 1 tail to a 98% level of confidence. The Cu distribution in the <12µm fraction is a less variable measure of changes in the <12µm Cu recovery, therefore, this was used to evaluate the impact of magnetic conditioning. Subsequently, magnetic conditioning was installed in both cleaner 1 circuits and the plant results monitored after this installation. Comparing the plant results immediately before and after this installation showed that there was a 20% reduction in <12µm Cu losses to the cleaner tail. INTRODUCTION The Cu-Au, Phu Kham Mine (PKM) is located within PanAust's Phu Bia Mining Contract Area in Laos, approximately 140 kilometres from the capital city, Vientiane. PKM is PanAust's flagship operation and the significant cash flow generated by PKM has supported PanAust’s growth, while contributing to a strong balance sheet. PKM comprises an open-pit mine and a conventional milling and flotation operation that produces and exports a Cu and precious metals concentrate. The concentrate contains around 23% Cu, 6 ppm Au and up to 35 ppm silver. Process Overview The PKM deposit consists of complex heterogeneous mineralogy horizons of Cu-Au stockwork and skarn mineralisation. It contains areas of soft-leached zones, overlying transition zones and supergene chalcocite dominant secondary Cu mineralisation and clay-rich gangue. Areas of high As and Zn also pose a challenge in treating the highly variable ore. In addition, hardness of the ore increases with deposit depth. The ROM is hauled to a primary gyratory crusher to produce a coarse ore stockpile with size distribution suitable for the 13 MW semi-autogenous mill. The SAG product feeds two parallel ball mills each equipped with a cyclone cluster producing a product particle size distribution of 80% passing 110 µm. The conventional flotation circuit consists of two parallel rougher banks. The rougher concentrates feed the regrind cyclone where the underflow is split and reports to two parallel, 3MW, M10000 IsaMills. The regrind mill discharge combines with the regrind cyclone overflow with a product particle size distribution 80% passing 25 µm and reports to the Jameson cell."

Jan 1, 2018

By Rodrigo Peroni, Euler Victoria

Knowing the depth of contacts between weathering zones in phosphate mines is determinant to define the stripping ratios and the mineralized zones. Contacts are gradational and difficult to define even in the drillhole samples, so the combination with geostatistical simulation techniques helps to define the contact zone and the grade distribution, providing a way to assess the probability of the occurrence and the positioning of contacts between the barren waste and the ore zones. These inputs are used in the scheduling, anticipating risks associated with mine planning scenarios. The results from an application to a case study showed a good improvement when compared to traditional techniques.

Jun 25, 2023

By Wilson Blake

The occurrence of rock bursts in some deep mines throughout the world constitutes a severe operational hazard. In addition to endangering the safety of the miners, the rock-burst problem is a major factor in mining economically in deep mines because of the loss of production and expense owing to cleanup and repairs following a burst. Developing means of controlling or eliminating rock bursts has been the subject of intensive research for over 50 years. While much has been learned about the effects of rock bursts, little is known about their basic causes; hence, control measures have been at best only partially effective--attested to by the number and severity of bursts that continue to occur throughout the world each year. In the Coeur d&apos;Alene mining district of north Idaho, the rock-burst problem continues as the silver and lead veins persist at depth. These veins are presently being mined at greater than 7,000 feet below the surface and will be mined to some 10,000 feet in the future. The majority of rock bursts in this district occur in pillars. While pillar bursting has been essentially eliminated in some deep-mining districts by longwall techniques, modification or application of this technique to the thin, irregular, and near vertically dipping veins of the Coeur d&apos;Alene district has not been found to be practical. The creation of pillars is a consequence of the horizontal cut and fill mining method used. Figure 1 shows a vertical longitudinal projection of the silver vein at the Galena mine, illustrating the mining method. Stoping progresses between raises and is carried upward between levels. A horizontal pillar is created as a stope approaches a mined-out level. Recent broad-band micro seismic monitoring of rock-burst-prone stopes by the Bureau of Mines has shown that potential burst zones could be delineated weeks in advance of a burst and that a definite sequence of events took place prior to the occurrence of a pillar burst (1). Hence, time was available for control measures to be effected when a stope pillar reached a critical burst geometry.

Jan 1, 1971

By J. L. Brinkman

"One of the most common emissions from detonating explosives are nitrogen oxides (NOx), which are potentially deadly if inhaled. Lab studies estimate emission quantities, though great variation is shown based on site-specific conditions, and lab tests may not fully represent field results. Field VALUES (have not been measured due to the vast area affected. OSMRE recently promised to release a ruling regarding surface mine NOx production. Once the ruling is implemented, it may eventually be necessary to monitor site-specific NOx production from blasting. A small unmanned aerial vehicle system (sUAS) is able to carry a NOx gas monitor, rapidly travel to the blast location, and to follow resulting clouds of dust and emission gasses. This project will perform laboratory tests to expand on current estimations, determine an optimal method for collecting data, and evaluate the ability for this unique application of sUAS to assist in health risk assessment for mine employees and nearby communities. Additionally, large initial NOx concentrations do not necessarily correlate to unsafe conditions, and this project will be ground breaking in observance of surface blasting emission dispersion. The project is still in early phases at the time of submission for this paper (Nov 1, 2017). Therefore, this paper focuses primarily on summarizing background research related to the project and a description of the project plan. INTRODUCTION Nitrogen oxide gases (NOx) are common emission by products of surface mine blasting. These gases can potentially cause risk to human health and safety, both for mine workers and communities near the blast site. However, these emission quantities are largely unmeasured and no attempts have been made to relate these VALUES (to human health risk. The primary objectives of this project are to determine actual quantities of emission gases produced during surface blasting, to evaluate immediate and long-term risks to nearby people, communities, and ecosystems, to develop a system for mine employees to easily monitor emission and risk levels, and then provide guidelines for mitigating health risks based on a location’s emission results. BACKGROUND Current research regarding health risk produced by surface mine blasting NOx emissions is extremely lacking. Estimations have been made based on laboratory research, though these same test results show wide ranges of possible gas quantities produced based on site-specific conditions. Even if these estimations are accurate, no method has been created to relate gas quantity produced to human exposure concentrations. To further understand this field, background research was studied pertaining to blasting emission gas formation, laboratory and field measurements, harmful effects of blasting emission gases, and relevant government regulations. Background on Blasting Emission Gases"

Jan 1, 2018

By Isabel Barton

This article describes and analyzes the history of research into the origins of the uranium-vanadium(-radium) deposits of the Paradox Basin. For several decades after their discovery in 1881, research was desultory and almost entirely descriptive, fluctuating with demand for vanadium and radium. Systematic geologic descriptions, accumulated between 1910 and 1950, supported rapid progress during a government-backed surge of research in the 1950s, when uranium was the chief commodity of interest. Most of the major theoretical innovations date from this decade, including the use of concepts from solution chemistry to identify the conditions and constrain the processes of deposit formation and alteration. Research from this time was highly influential in geology at large, providing the model for sandstone-hosted uranium deposits worldwide and numerous new minerals and mineral structures. After about 1960, mine production remained high but research dwindled, and most new advances were to the details of the hydrothermal model of ore formation rather than its core concepts. By the end of the 1960s, the deposits were understood to have formed at the mixing interface of an oxidized, metal-bearing water with a reducing fluid of debated origin. Research was desultory over the ensuing decades; the source of the metals and the nature of the chemicals constituting the trap were not clearly established. They remain questions today, as do factors like the relationship between ore mineralization and the geologic history of the basin. (More in the full paper.)

Jan 1, 2025

By Robert J. Timko

New methods of reducing stopping leakage have been investigated by Mine Safety Appliance Research Corporation, working under contract to the U. S. Bureau of Mines. It was found that proper construction techniques are far more important in reducing leakage than the type of sealant used, provided the sealant has sufficient adhesion and strength. Leakage could also be substantially reduced by brushing on modified mortar sealants rather than using the accepted method of trowelling them on.

Jan 1, 1982

By O. Lopez

"Stringent regulations and increased arsenic presence in ore bodies being exploited have created the need for cost effective and environmentally compliant technologies to remove selenium and arsenic from mine waters and metallurgical waste streams. Existing treatment methods have high life cycle costs and/or produce residues that, due to their unknown stability over the long-term, may represent future liabilities. This results in high compliance costs and uncertainties which negatively impact existing operations and projects in permitting. Selen-IX™ is a new ion exchange based process that selectively removes selenium from mine impacted waters down to 1 ppb while producing a stable inorganic iron-selenium product. Results of piloting completed on streams generated from coal and copper-gold deposits are presented along with preliminary equipment sizing and life cycle costs of full scale treatment. An example of a commercially available system for arsenic removal using sulphide precipitation is presented. The benefit of this treatment method is discussed based on recently completed technical feasibility assessment including laboratory testing and preliminary engineering design. INTRODUCTION Selenium Due to the chemical similarity between selenium and sulfur, selenium substitutes sulfur in many minerals that can be found in a wide range of deposits including coal, base metal, precious metal, phosphate, and uranium. One of the main environmental challenges facing the industry in North America today is related to the removal of hexavalent selenium, e.g. selenate, to ultralow levels, typically between 1 to 10 ppb, from large flows of often cold water containing less than 1,000 ppb of selenium. Recent studies commissioned by the industry identified biological selenium reduction systems as the best available technology. Although the biological selenium reduction process is commercially proven in certain applications to remove selenium to ultralow discharge levels, the technology has been primarily applied to relatively low and constant flows of warm water produced by the Flue Gas Desulfurization (FGD) scrubbers in the power generation industry. The wide spread adoption of this treatment method by the mining industry is hindered by high capital and operating costs associated with treating large flows of cold water, lack of data and knowledge about the long term stability of solid residues produced by this treatment, and limited capacity of biological systems to respond to sudden changes in flow and/or mass load of contaminants. Furthermore, it has been reported that reaching discharge limits less than 3 ppb could be a challenge and that polishing treatment for the removal of BOD and phosphate maybe required to avoid the impact of the biological treatment which requires organics and nutrients, on aquatic environment downstream of treatment plants. Alternate treatment systems are being developed to overcome and/or completely avoid some of the challenges of biological systems. One such treatment system is BioteQ’s Selen-IX™ process which is purely physico-chemical treatment system."

Jan 1, 2015

By D. Kruse, M. Sanaei

"A three dimensional nonlinear finite element model was constructed to simulate and analyze the behavior of large diameter segmentally lined shafts when subjected to seismic waves. To reduce computation time, a less complex shell model was also constructed. Transient excitation was applied to the supported nodes of both models, at the base of the shaft, with a time-function representing the 1994 Northridge earthquake. The models are developed at the end of an original phased construction-stage analysis of the shaft. Displacements, forces and moments are monitored and compared during the analyses steps. During the initial 15 seconds of the earthquake, the top and bottom of the shaft show similar displacements. The maximum horizontal displacement within the shaft is approximately 3.5 inches in the solid model and the shell model results conform to this by a factor of 50%. Keywords: Segmentally Lined Shaft, Soil Structure Interaction, Seismic Analysis, Finite Element Modeling, Ground Modification INTRODUCTION TO SEGMENTALLY LINED SHAFTS Large diameter segmentally lined shafts (SLS) are underground systems, constructed sequentially using precast concrete segments to form a ring which provides both temporary earth support during excavation and permanent structural support. The segments are connected via alignment pins, bolts, packer material and other structural components that ensure the continuity of the SLS. In this analysis, the construction process uses a top-down sequence wherein each soil layer is excavated, damp-proofing is installed and concrete segments are assembled to form each ring. This process is repeated until design depths are achieved completing the shaft. It is known that cylindrical structures sustain lateral (earth) pressure mainly through the mechanism of hoop-stress. As Timoshenko’s ring theory goes, a cylinder shell structure is prone to buckling under external pressure [1]. In typical designs of small diameter shafts and tunnel linings with small diameter to wall thickness ratios, nonlinear buckling analysis (i.e., nonlinear geometric analysis) is not considered, since the buckling capacities for those structures are much higher than typical pressures encountered at their design depths. However, in shafts with large diameter to wall thickness ratios, buckling could become a critical issue. In any given mode, as buckling occurs in a ring, some sections of the structure move inward while alternating sections protrude. Although the presence of the surrounding soil could mitigate the buckling by resisting the movement (Soil structure interaction) seismic loads can cause ground movements and lateral pressures, exceeding the capacity of the structure. It is therefore essential to design the load bearing capacities of the shaft to minimize the possibility of any catastrophic failure due to earthquakes. This study explores the structural response of the SLS when subjected to seismic loads."

Jan 1, 2016

By Eddy J. Jacques

When the automatic control of a ventilation process is considered, and supervising expert systems need to be designed, an important problem to address is: what will be the optimal set points of the regulators that should meet a certain number of independently formulated requirements, distributed over a ventilation network? The set of these requirements, expressed in terms of air flow quantities or differential pressures in certain airways, need not be consistent. Their number is not limited by the number of available regulators, nor by their nature, i.e. passive or active. Moreover, they may be subject to upper or lower limit values. The method described here addresses this problem and tries to provide a tool that should allow to calculate the set points of all the regulators as a global and optimal solution with respect to this set of distributed requirements. The pure mathematical developments in this paper are kept as short as possible in order to allow more room for the description of a relevant example.

Jan 1, 1991

By W. Nahas, T. C. Watson, A. R. Maycock

The development of roasting technology for the oxidation of sulfides in refractory gold ores is discussed. Case studies covering operations dating from the mid-1930&apos;s to the present day are used to illustrate this development. The roasting of ores and concentrates is reviewed and various gas cleaning flowsheets are discussed with particular reference to environmental requirements. A sequence chart is provided to show the development path of a potential roasting project.

Jan 1, 1990

By J. Hunter

The Highland Uranium Project in Wyoming is an in-situ leach (ISL) facility owned and operated by Power Resources Inc. It is the largest uranium producer in the U.S. and the largest uranium producer by ISL in the western world. With its limited capital investment and low operating costs, the ISL technique has been demonstrated to be an effective and environmentally sensitive method for recovering minerals from these low grade and otherwise uneconomic orebodies.

Jan 1, 1996

By B. T. Field

Pyroprocessing systems range from low temperature dryers to high temperature reactors. The materials and process requirements cover a broad spectrum. It is not the intent of this paper to do a detailed examination of individual processes and equipment, since that can be found in a multitude of other sources; rather it is the intent of this paper to examine the key process variables and offer empirical guidelines to assist in a user?s overall evaluation.

Jan 1, 1998