Search Documents

By J. Muralha, L. Lamas

"Given the results of triaixial tests, regressions are commonly used to evaluate the parameters of failure criteria that model intact rock strength and to perform statistical inferences used to evaluate characteristic values defined in EC7. Statistical robustness of these inferences is affected if the basic hypothesis underlying regression are not met, namely homoscedasticity (constant variance of the errors). This paper presents analyses of 23 sets of triaxial tests, starting by the evaluation of the regression parameters of the Mohr-Coulomb linear criterion and of the Hoek-Brown non-linear criterion, followed by carrying several statistical tests to check the homoscedasticity null hypothesis of independence between the variance of intact rock strength and the confining stress.INTRODUCTIONThough rock engineering design is clearly included in the scope of Eurocode 7(EN1997-1), its implementation raised a wide discussion regarding the applicability of structural safety concepts to geotechnical design of construction works in or on rock masses. The basis of the limit state design philosophy adopted in EC7 is that, for each particular design situation, all the possible limit states for a structure, or part of it, shall be considered and that it shall be demonstrated that the likelihood of any limit state being exceeded is sufficiently small. Though EC7 allows the limit states to be verified by one or a combination of methods, use of calculations is by far the most used, and it is often confused with the EC7 itself. It involves using characteristic values of actions, ground properties and geometrical data, as well as obtaining their design values by the partial factor method.Characteristic value of a given material property is defined in Eurocode (EN 1990) as: “value of a material or product property having a prescribed probability of not being attained in a hypothetical unlimited test series. This value generally corresponds to a specified fractile of the assumed statistical distribution of the particular property of the material or product”. As regards the design value of a material or product property, according to the Eurocode it is a “value obtained by dividing the characteristic value by a partial factor”."

Jan 1, 2015

By R. Barany

In this paper, closed expressions have been obtained for the frequency spectrum of a Born-Karman square lattice in terms of elliptic and hyperelliptic integrals. This work is part of continuing research by the Bureau of Mines with the thermodynamic properties of metals and minerals. Although other workers have obtained various types of approximations for the general case of the frequency spectrum of a square lattice, no one previously has obtained closed analytic expressions for this spectrum. To understand the optical and thermodynamic properties of crystals, several investigators have studied the distribution of frequencies of normal modes of vibration of the crystal lattice. Born and Karman3 laid the foundation for the theory of lattice dynamics and obtained detailed results for the case of a one-dimensional lattice. Blackman4 used numerical techniques to estimate the frequency distribution of a two-dimensional square lattice. Mbntroll5 analytically determined the frequency distribution of a square lattice for a particular value of the force constants. He also studied the more general problem and obtained some analytic approximations, using the method of moments. However, the calculations by this method were so difficult that it was not always practicable to carry them out. Van Hove6 and Montroll7 studied the nature of the singularities in the frequency spectrum of both a two and

Jan 1, 1962

By X. Zhang, Z. T. Yuan, C. Zhang, H. M. Zheng, X. M. Wang, L. X. Li, N. Li

In metal mines, comminution is commonly used to liberate minerals for subsequent mineral concentration processes, such as flotation, magnetic separation and gravity separation. However, ores are aggregates of valuable minerals and their disseminated gangue minerals, and these minerals exhibit diverse comminution behaviours. In carbonate-bearing iron ores, hematite, siderite, and quartz are the predominant minerals, of which hematite is the objective recoverable mineral. In this regard, the present study aimed to identify the imperfections in siderite minerals by X-ray computed tomography (XCT), and thus quantitatively characterise their size and shape in terms of Feret diameter and aspect ratio, as well as other parameters. XCT images indicated the protogenetic ubiquity of pores <5 μm in diameter and cracks of 7-8 μm inside siderite particles. In the ground product of artificially mixed siderite and hematite, siderite particles were smaller than hematite particles. Siderite particles had a larger surface area and greater surface roughness than hematite particles of the same volume, which was attributable to the intrinsic holes and cracks in siderite particles. This study provides an insight into the relationship between the inherent imperfections of minerals and their comminution properties. Keywords: Siderite; X-ray computed tomography; particle imperfections; grinding behaviour; sliming

Jan 1, 2020

By K. Turgeon, J. -F. Boulanger, L. Whitty-Léveille, C. Bazin

"Several companies targeting Rare Earth Elements (REE) around the world have completed a Preliminary Economic Assessment showing positive project financial results. Although REE ores may contain high REE value, financing these projects remains difficult in part due to the number of processes required to valorize the elements and the relatively low yield of these processes. Direct ore leaching without the production of a concentrate may reduce the capital and some operating expenditures through process simplification, and increase revenues because of REE recovery improvement.A silicate REE ore is used to test various hypotheses regarding whole ore processing and to develop a simplified flowsheet. An atmospheric leach (200 kg/t H2SO4) of crushed whole-ore containing 0,6% REE, followed by impurity removal and REE precipitation recovers 80% of the REEs in a solution containing REE and Th. The high value contained in most REE deposits makes whole-ore approaches worth considering for most projects, given the losses of valuable species typically associated with the production of a REE mineral concentrate from the ore. INTRODUCTIONRare Earth Elements (REE) find applications in modern and clean technologies, whether civil, industrial or military. With China producing more than 90% of the world’s REE, the embargo imposed by this country in early 2010 increased REE prices for a three year period. With prices having shrunk back many-fold from their peak value, projects put forward during the hike are struggling to secure financing. Owing in part to unconventional processes such as acid-baking and solvent extraction, REE plants are high capital cost and high operating-cost units, and present technological risks (Verbaan et al., 2014)."

Jan 1, 2016

By F. C. Harris, S. J. Gaab, J. Sattarvand, S. Duzgun

Underground mines are inherently dangerous due to potential hazards such as fires, explosions, and caving of rock. Although these events are rare, once they occur a speedy and safe egress of mineworkers is critical to survival. Static evacuation systems use exit signs or directional lines but can get obstructed or be hardly visible in smoky or dusty conditions. This paper presents the investigation of the effectiveness of a smart evacuation technology in underground mining, where a real-time guidance system leads individuals on an optimised path to the egress while avoiding danger zones, compared to conventional practices. Participants simulated an evacuation from a virtual reality mine, using the conventional system and the smart evacuation system with real-time guidance. The highest reduction in evacuation time using the smart method amounted to nearly 40% on average. Moreover, 83% of participants preferred the smart guidance system, and agreed that it could enhance safety.

Sep 1, 2021

By E. M. Frost

"A new apparatus has been devised for quickly and precisely analyzing natural gas for its helium content. The following outstanding advantages make it far superior to any equipment now available for the purpose.3/4/5/6/1. It enables more rapid determinations to be made.2. It has far greater sensitivity than previous apparatus. 3. It is portable.Fifty or more samples may be analyzed in an 8-hour day with the new apparatus and procedure. A maximum of about 10 samples per day could be analyzed with previous apparatus. In the apparatus described, the volume of pure helium obtained from a sample is determined by measuring the pressures created by that pure helium when it is expanded into a constant calibrated volume. In older methods the pure helium separated from a sample is pumped into a burette and measured at atmospheric pressure. The new apparatus and Procedure used with it reduce the average time for an analysis from about 40 minutes to less than 10 minutes,Samples containing a few thousandths of a percent helium may be analyzed as readily as samples containing 1 percent or more, This was not possible with former apparatus. Duplicate samples containing a few thousandths of a percent helium have been analyzed, results checking to one ten-thousandth of a percent. Attempts to measure a corresponding volume of helium in a burette at atmospheric pressure become futile. The ability to determine very small quantities of helium has become of great importance recently in gas- and oil-field engineering studies such Os the utilization of helium as a tracer gas in following the movement of gases through underground structures.A complete apparatus was recently carried more than a thousand miles in a passenger automobile. It arrived without breakage, was .set up and ready to make an analysis in a few hours. .Former apparatus was not portable. The portability of the present apparatus permits taking the apparatus to the field for more efficient prosecution of field engineering problems. The only services required in the field are electricity, tap water, and a source of liquid air or liquid nitrogen.The principle involved is based upon the fact that large volumes of all the constituents usually found in natural gas, except helium, are adsorbed quantitatively on cocoanut charcoal that has been cooled to the temperatures of liquid air. A volume of sample is measured and transferred to a tube of cocoanut charcoal maintained at the temperature of liquid air. After adsorption of all the constituents other than helium, the charcoal tube is connected to a sensitive pressure-measuring device, and the Percentage helium originally in the sample is calculated from two pressure readings and the volume of the original sample."

Jun 1, 1946

By H A. Challenor

Eyewash safety showers located in remote hot environments may be unsafe to use due to excess water temperature and high risk levels of water borne bacteria such as Legionella. Australian Standard AS 4775 specifies that dispensed water shall be bacteria free and have a maximum temperature of 37.8&#176;C. Legionnaires disease is contracted when water aerosols containing Legionella bacteria are inhaled.Laboratory tests show 30 to 70 times more aerosols are generated by showers operating at 38&#176;C than with showers operating at 25&#176;C. Furthermore, excess temperature in flushing water can cause burn injuries leading to hospitalisation, skin grafts and/or permanent scarring. Excess temperature also increases the rate of reaction to corrosive substances, opens pores in the skin to allow greater dermal penetration and can cause dizziness and fainting by dilating blood vessels and reducing blood pressure.CITATION:Challenor, H A, 2017. Managing excess temperature and high risk levels of Legionella bacteria in eyewash safety showers, in Proceedings Iron Ore 2017, pp 337–346 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 24, 2017

By A. Frits van Tol, Rodriaan Spruit, Jan H. van Dalen

"Abstract In recent years, there have been major problems with deep excavations in urban areas supported by diaphragm walls. In some cases, like the fatal Nicoll Highway collapse in Singapore the quality of the D-walls was not the cause. However in other projects, like the problems with the major leak in the walls of the Boston Big Dig and with leakage in a few projects in Belgium and The Netherlands was related to poor D-wall quality. Leakage through the D-walls at the joints in deep excavations led in these cases to very serious settlement behind the walls, in the case of the North- South line in Amsterdam, there was severe damage to historical buildings. This paper describes ongoing research that focusses i on acquiring more knowledge on and improvement of D-wall installation, in particular the flow process prior and during casting ii on the detection of anomalies prior to excavation and iii on the composition of the concrete mixture in view of a better and more sustainable concrete quality of D-walls.INTRODUCTIONIn the case of deep excavations in urban areas close to neighbouring buildings, diaphragm walls are one of the best feasible solutions for the retaining structure. Although the costs of D-walls generally exceed the costs of alternative wall solutions, the advantages are decisive in many situations. The main advantages of D-walls are the limited impact of the installation on the built environment, the high stiffness and bearing capacity and the retention of water, even at considerable depths. This makes Dwalls often the preferred solution for deep excavations Sometimes the D-walls are the temporary support while for the final stage a complete concrete box is constructed in the excavation. In many other cases the D-wall has the permanent function of retaining soil as well as groundwater.In the last ten years, there have been major problems with deep excavations in urban areas supported by diaphragm walls. In some cases, like the fatal Nicoll Highway collapse, 2004 , the quality of the Dwalls was not the cause. In other important failures like the collapse of the Archives in Cologne, 2008 and Dubai Infinity Tower Flooding, 2007 a combination of design and quality issues played a role. However, the major leak in the walls of the Boston Big Dig was related to poor D-wall quality (McNichol, 2000). Van Tol et al, (2010) describe a number of case studies in Belgium and the Netherlands, with leakage through the D-walls at stop end joints. In several cases with deep excavations these leakage caused serious surface settlements behind the walls. In the case of the North-South line in Amsterdam, there was severe damage to historical buildings. All these cases have generated considerable additional costs and delays, and subsequently public and political concern. Van Tol et al. (2010) present several possibilities to improve the quality of D-walls.Other disputes related to D-walls deal with the quality of the concrete and the sustainability of D-walls applied as a permanent wall. In particular the porosity of the concrete cover is sometimes problematic."

Jan 1, 2014

By Alfred E. Pugsley

PAYMASTER CONSOLIDATED MINES, LIMITED, began an investigation into the economy and use of detachable bit drill-steel in June, 1937. This investigation has continued to the present time, and was made necessary by transportation and distribution difficulties that had arisen through the use of standard steel in three widely separated mine areas serviced by a central steel-sharpening shop. Detachable bit drill-steel performance was first studied in the workings of No. 2 mine, where the rock being drilled was composed mainly of porphyry or tourmaline, and where standard drill-steel transportation costs had been excessive. The results obtained in this early work definitely established the economy of detachable bit drill-steel at No. 2 mine. This conclusion was reached when the &apos;re-grind&apos; system of re-sharpening dulled detachable bits was 1n use. Preliminary observations on the performance of detachable bit drill-steel in the quartz-carbonate veins of No. S and No. 6 mines gave encouraging results, and warranted a large-scale investigation under practical mining conditions. All drilling operations were gradually changed over to use of detachable bit drill-steel. This change was completed by February, 1938.

Jan 1, 1939

By Bo Hyun Kim, Mark K. Larson

Fault-slip bursts induced by mining activities can result in severe damage to nearby mine development. In general, engineers designing rock support in burst-prone mines not only need to consider stress redistribution resulting from excavation, but also dynamic loading that results from seismic waves generated by large mininginduced fault-slip events. In this study, we simulated dynamic waves in sedimentary rock from a blasting source and from a mining-induced-seismicity source using a Universal Distinct Element Code (UDEC) model with discrete fracture networks (DFNs). Our purpose was to investigate the stability of openings and the adequacy of existing support systems at an underground limestone mine in South Korea. A baseline model with only static loading was also simulated, which verified observed stability under such conditions. The results indicate that the current support system of shotcrete lining is likely to work well under dynamic loading caused by blasting. However, when the dynamic source was a far-field fault-slip event, the dynamic loading exceeded the support capacity of the shotcrete lining. Thus, if a mine is operating in ground with an elevated risk of mininginduced fault slip, mine engineers should consider seismic wave propagation and ground motion distribution from a remote, mining-induced fault-slip event to determine a suitable support design.

Jul 1, 2023

By H. S. Kalman

A table of factors for rapid, accurate calculation of the volume of pure helium in cylindrical steel containers, at base conditions of 14.7 psia and 70° F, is presented. The table covers a pressure range from 10 to 10,000 psin in 10-psi increments and a temperature range of 0° to 120° F in 2° increments. The volume of helium is calculated from the observed pressure and temperature of the helium, expressed as a factor from the table, and the known internal volume of the container. The calculation requires a single multiplication. A discussion and evaluation of the accuracy obtainable and a derivation of the formula used (which takes into account compressibility of helium, thermal expansion of steel containers, and the stretch of steel due to internal pressure) are presented. An example showing how the table can be used is given also.

Jan 1, 1968

By Carnevale Francesco, Bracci Laudiero Alberto, Pampanin Piero

"SummaryIn the Port of Naples a slurry wall has been realized through a sandy layer up to a deep tuff layer using the Cutting Soil Mixing technique.The executed panels have dimensions of 2.8 m x0.65 m in plan and a total length of 25 m. Primary and secondary panels have been executed using the wet to wet technique. During the panels execution the following parameters had been measured: injection pressure, injected volume, verticality. At the end of the works an exploratory campaign has been carried out through boreholes collecting samples for laboratory tests in order to verify the diaphragm thickness and its physical and mechanical properties (i.e. unit weight, unconfined compressive strength).The interpretation of the collected data allowed to verify the efficiency of the method, the volume of slurry loss due to permeation during the panels execution, the quantity of the obtained spoil compared to the volume balance equation, both for the sand and the tuff layer.Eventually, the measured physical and mechanical characteristics of the panels have been correlated to the execution method performed.IntroductionIn the Naples Port area there is a polluted site which has to be hydraulically isolated in order to prevent the pollution of the groundwater that flows from land to the sea through the Port area. A hydraulic cut-off wall has to be realized and particularly a slurry-wall realized using the CSM method had been executed.To date, two stretches have been executed, 140 an 110 m in length respectively, as shown in Figure 1 and Figure 2.After execution, the slurry-walls have been investigated with boreholes. In-situ and laboratory tests on the recovered samples of grout have been carried out; furthermore, the geotechnical parameters of the mix composing the wall have been measured."

Jan 1, 2014

By J. S. Kirkaldy, D. G. Fedak

The extra degree of freedonz introduced by a second independetzt concentration in a tenzary system gives rise to the possibility of unstable planar phase interfaces in semi-infinite diffision layer couples. Diffusion paths which pass continuously in and out of too-phase regions of the phase diagram but which are not coincident with tie-lines give rise to super saturated zones which may be either adjacent to or isolated from planar phase interfaces, with corresponding nonisolated or isolated precipitates. Nonisolated precipitates are equivalent to morphological development of the interface. Selected couples in the ternary systems Fe-Ni-Cr and Cu-Zn-Sn have been examined nzetallographically and ifz the latter case both isolated and uo~zisolated precipitates have been observed. The diffusion path in one of the couples showing interface morphological developtnent has been examitled using electron probe microanalysis. IGNORING the spurious effects of preferential grain boundary diffusion and anisotropic crystal growth7 it can be unequivocally stated that it is impossible for a binary isothermal diffusion couple constructed of two unsaturated phases to sustain a nonplanar phase interface. Consider for demonstrative purposes the schematic phase diagram of Fig. l(a). Given an initial flat phase interface, semi-infinite boundary conditions and the internal boundary condition fixed by the constitution diagram, xB = xB(T), the unique solution of the diffusion equation requires a persistent flat interface. No other solution is possible. If, however, we anticipate the involvement of surface tension, then the internal boundary condition must be written xB = xB (T,Y) where r is the radius of curvature of a hypothetical nonplanar interface. The introduction of a new parameter such as r can be equivalent to the release of an internal constraint, so that a stable nonplanar interface may be possible after all. Consider a perturbation to the interface as indicated in Fig. 1(b). According to the Ostwald-Freundlich equation: which is applicable to a system of this constitution, the solubility of A in the matrix ß ,xB (Y), at a point of curvature r is given by where Va is the molar volume of the a-phase, R is the gas constant, and a is the interfacial tension. Since the right hand side is positive, xB(r) >xB cm, as indicated in Figs. 1(a) and 1(c). Accordingly, the perturbation will carry the interface concentration in a direction which is opposite to that which would sustain local equilibrium. Such a perturbation is necessarily moderated and the system is returned to its initial condition. This result is general for all binary couples since we can regard an interfacial perturbation as an attempt to precipitate within un-

Jan 1, 1962

By Christopher Newman, Robert Dupuy, David Newman

"The development of a multiple level underground mine is a complex task in which geology, engineering, ground control, and unit operations are integrated into a single mine design. The components are inter-dependent and must function cohesively to ensure a profitable underground mining operation. To optimize reserve recovery, mine planning should begin from the lowest level and progress up. This limits any misjudgments or oversights of a given level affecting the underlying levels and ensures the ability to maximize recovery from each level.Mine planning should start with the exploration and characterization of the geologic setting. Once the reserve geology and quality is well understood, then mine planning can begin with respect to the following:,Orientation of mine works with respect to horizontal stress,,Access to the reserve,,Determination of opening widths,,Selection of back, floor horizons and pillar centers,,Selection of development and secondary mining heights,,Appropriate interburden thicknesses, and,Examine the stability of the multiple level mine through numer¬ical modeling.The multiple level mine design process and decisions are presented through a case history example. The theme is that there is one opportunity to “get it right” as well as many chances to overlook a small aspect within the design that will plague the mine throughout all levels and through the entirety of its operating life.INTRODUCTIONAs surface quarries reach their economic stripping limit and encroach on mineral and/or reserve boundaries, they approach the end of surface mineable reserves. Furthermore, modern urban sprawl has placed previously remote surface quarries within suburban development and neighborhoods, leading to significant increases in noise, dust, and vibration grievances by the community and regulators (Newman, 2017). Many mining operations have begun year-round production of underground reserves to meet growing market demands. This does not permit the typical sequence of stripping overburden in the winter to provide limestone to mine during the construction season. Underground stone mining operations in the United States commonly utilize a room-and-pillar mine layout with drill-and-blast production methodology for the development of the reserve. Within the Midwest and Eastern regions, thick and flat-lying limestone formations lend themselves to the utilization of multiple level mining layouts. While a multiple level mine plan will increase the overall recovery of the reserve, greater overburden depths, multiple level geometry, and the presence of discontinuities all require an emphasis on ground control for the planning and development of a safe and productive multiple level underground stone operation."

Jan 1, 2019

By William G. Pariseau

"This contribution describes linkage of stress concentration at the face of tabular excavations, for example, longwall coal mine panels, at a meter scale to surface subsidence at a kilometer scale. Joints are considered according to orientation and spacing at an intermediate scale. A new dual-node, dual-mesh technique based on first principles uses a multi-scale technique that allows for computing whole mine surface subsidence while also allowing for computational details of stress, strain and displacement about main entries and pillars, panel entries, and bleeder entries. The technique is implemented in a conventional continuous Galerkin finite element program that has been in use for many years.The advantage of the dual-node, dual-mesh technique is the capability to do a whole mine analysis that takes into account interaction between all sections of a mine where stress transfer over long distances is often the rule rather than the exception while at the same time allowing for details of stress concentration at working faces where caving is initiated and subsidence begins. The technique, outlined recently during ARMA 2014 (Pariseau, 2014), is applied to an underground coal mine in central Utah where mines are developed from outcrops in steep canyon walls. Meshes contain over 10 million, three-dimensional nodes; runtimes are typically overnight, as a practical matter. Results compare favorably with mine subsidence measurements made over a period of several years and show the capability of this new technique to provide useful design guidance for tabular deposits such as underground coal mines. The role of variability or uncertainty in strata properties is illustrated in element safety factor distributions about development, bleeder and main entries and pillars. Such details are new in this contribution. Energy tracking for mine-induced seismicity is also new. Results show a high correlation between number of events and failed elements and suggest a simple index to mine induced seismicity."

Jan 1, 2015

By Tom Tallone

In the majority of metal and nonmetal mining operations, narrow vein deposits are being mined with slusher hoists. Thin; method of mucking is costly, due in part to its inherent labor intense operation and to its inability to muck 100 pct of the deposits. Mechanized equipment would greatly improve the material handling in narrow vein mining and would dramatically reduce the operational cost. The Compact Loader/Trammer, known as the "mini-mucker" has been developed to increase productivity of the load/haul/dump portion of the typical narrow vein mining cycle. This is Volume II of the final report and concerns the operation and maintenance of the mini-mucker. Volume I covers a general and design review of the activities on the subject contract and are available under separate cover.

Jan 1, 1985

By Paulo Chaves, Márcia Gonçalves, João R. S. Carvalho, Fernando J. A. S. Barriga, Edgar Carrolo, Tiago Luna, Ricardo Rato, Anabela Bento

INTRODUCTION For the last decades, deep-sea marine resources such as seabed massive sulfides (SMS), polymetallic nodules and ferromanganese crusts (Fe-Mn crusts) have received an ever- increasing amount of attention worldwide for their abundance in critical metals and potential commercial value. This interest has mostly been driven by the growing world demand for raw materials, in particular for high- and green-technology applications (e.g., hybrid and electric cars, batteries, photovoltaic solar cells, cell phones, super magnets), as well as by industrialized countries governments other than BRICS states need to secure a more diversified supply of metals, resulting in a new deep ocean exploration boom. Since the oceans and its resources are increasingly seen as indispensable for humans needs and their challenges in the decades to come, this boom increments pressure on marine areas, either in international or within countries economic exclusive zone (EEZ). Since 2002, the International Seabed Authority (ISA) has signed up 29 contracts with several entities and national governments from multiple countries (e.g., Japan, China, Germany, France, Russia, India, Rep. of Korea, UK, Canada, Brazil) for exploration for deep-sea mineral resources in international waters, either for scientific or commercial proposes, which together cover over 1.3 million km2 [1]. In turn, over 300 exploration licenses, covering more than 650,000 km2, have been granted within the EEZ of Pacific countries such as Papua New Guinea, Tonga, Fiji, Solomon Islands and Vanuatu [2, 3]. This number is expected to increase very rapidly, as 77 countries have proposed to the United Nations the extension of their continental shelf in order to extend their EEZ and jurisdiction over potential deep-sea mineral resources [4]. Its estimated that 42% of the potential areas for SMS occurrences, 54% for cobalt-rich Fe-Mn crusts, and 19% for polymetallic nodules lie within the EEZ of coastal countries [5]. In addition, a huge amount of seafloor is yet to be explored and evaluated. Combined, the size of the granted exploration areas represents less than 10% of the overall area thought as most favorable for the occurrence of the 3 types of deep-sea mineral resources above mentioned. This means that today’s assessments on deep-sea mineral resources are only a rough approximation.

Jan 1, 2018

By Walter G. Kutschke

Four significant soil nail wall projects in the eastern United States were recently completed with a combined area of 175,000 square feet of finished shotcrete surface. These projects required the use of innovative design and construction methods in order to address various challenges, including slide-prone back slope materials, perched water, highly erodible rock materials, curved wall alignments, very tight construction tolerances and unexpected subsurface conditions. Special focus is given to issues such as bench excavation, soil nail installation methods, shotcrete mix design, anticipated shotcrete quantities, shotcrete nozzlemen qualifications and weather conditions, in order to provide a lessons-learned database for future soil nail wall design and inspector considerations. These projects also underscore the importance of design engineer and soil nail wall contractor qualifications as well as effective communication with the owner.

Jan 1, 2007

By Mandeep Singh

The smelting of lead ores has been carried out in southeast Missouri for centuries, and modern smelting practices have generated a variety of waste products. Lead blast furnace slag is one such product, which typically contains 10% zinc, 25% iron and 2% lead. This slag has often been stockpiled on the producing smelter site and accumulations have now reached several million tonnes. It is possible that in the near future these slags will be classified by the federal Environmental Protection Agency as hazardous, and therefore there is considerable interest in possible treatment processes to render the slags non-hazardous by removing the offending metallic elements. To ensure that the overall slag processing costs are kept to a minimum, it is imperative that lead and zinc be recovered in a form suitable for sale or further processing. There are two generic routes for processing blast furnace slags and they involve hydro-metallurgical or pyrometallurgical techniques. With hydrometallurgy, the slags would be leached directly and the metal values recovered from purified leach solution(s) by electrowinning. One problem with processes of this type is that the zinc and lead grades of the slags are low and the iron content is high, and thus the economics of metal production are often not favorable. For pyrometallurgical processing (1), it has been shown that the slags can be fumed to produce an oxide dust containing all the lead and zinc, and representing only a fraction of the weight of the initial slag. The oxide dust may then be processed hydrometallurgical to recover zinc and lead.

Jan 1, 1992

By P To, A Sharp-Paul, S Jones, C Monahan

A key environmental management issue associated with mining projects is tailing disposal. In high rainfall environments this is particularly challenging and generally requires the discharge of excess water from a tailing dam to adjacent streams or coastal waters. Such discharges can potentially have adverse impacts on downstream water quality and the environmental values associated with these waters, such as providing a drinking water supply for local villagers, maintaining a fisheries resource or protecting a fish species of high conservation significance. An alternative to the construction and operation of a conventional tailing dam is Deep Sea Tailing Placement (DSTP). The key features of such a system are:Discharge of the tailing slurry at considerable depth (approximately 120 - 150 m) below the oceanÆs surface. This requires a pipeline to be laid from the process plant to a mix tank, where the tailing is mixed with seawater and entrained air released. The pipeline then continues down the ocean floor to the required discharge depth, which is below the surface mixed layer and the euphotic zone. After discharge, formation of a density current which continues to descend along the ocean floor as long as the slope is sufficiently steep. Final deposition of the tailing in an area where the slope of the ocean floor is insufficient to maintain the density current. This typically occurs at depths of more than 800 m. Water quality issues associated with DSTP include: Impacts on the oceanic water column due to the formation of subsurface plumes which break away from the descending density current. The occurrence of elevated concentrations of contaminants in the interstitial waters of the deposited tailing solids. Fluxes of contaminants from the tailing deposits into the overlying oceanic water column. This paper discusses the water quality aspects of DSTP with particular reference to a case study in Papua New Guinea. The evaluations undertaken as part of the DSTP impact assessment included consideration of both the short- and long-term chemical behaviour of contaminants and bioassays, within the appropriate water quality assessment framework.

Jan 1, 1999