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By Gabriel Gonçalves Pessoa de Castro

O trabalho teve por objetivo produzir uma liga Al AA1070 com granulometria fina a partir de um material com granulometria grosseira, por meio de deformação plástica severa (DPS) aplicada por prensagem por canais equiangulares (ECAP) via rota C, bem como esclarecer e avaliar os mecanismos responsáveis pela evolução microestrutural durante este processo de prensagem. O processo empregou a rota C com 5 passes consecutivos a frio e acumulou uma deformação ?5 = 5,95. O material de partida é proveniente de um processo de laminação a quente, com uma microestrutura de grãos grosseiros com tamanho de grão de 16 ± 18 µm. Foi realizada a caracterização microestrutural com o auxílio das técnicas de microscopia eletrônica de varredura (MEV) e de difração de elétrons retroespalhados. O refinamento microestrutural foi realizado eficientemente alcançando uma microestrutura fina, observou-se uma redução de 80% alcançando um tamanho de grão de 3,38 µm, e um aumento da fração de contornos de alto ângulo passando de 23% a 46%. A partir dos resultados obtidos nas análises conclui-se que os mecanismos responsáveis pela evolução microestrutural foram os processos de subdivisão por meio de fragmentação e rotação de grãos, recuperação e recristalização dinâmica.

Aug 16, 2017

By Christopher J. Bise

INTRODUCTION Perhaps no other area reflects the art as well as the science of mining-engineering design quite as obviously as strata control. This is due to the fact that the design of mining structures is difficult because rock rarely behaves as a homogeneous medium. Further, the original state of stress and the mechanical proper- ties of the in situ rock are somewhat difficult to deter- mine. However, those aspects that are hard to treat mathematically can and have been successfully approached by model studies and in situ measurements. This chapter will review the fundamentals of strata- control design and will provide examples of applications to typical problems. STRESSES AROUND MINE OPENINGS A close examination of Fig. 1 reveals that, prior to mining, stresses exerted in the overburden can be in both the horizontal and vertical directions. In the example problems of Chapter 1, it was shown that the maximum compressive stress (uv) at any depth (D) below the surface can be approximated as follows: [ ] Further, the lateral stress (oh) is related to the maxi- mum compressive stress by utilizing Poisson's ratio (µ): [ ] As soon as a heading is driven, such as the one in the coal seam shown in Fig. 2, the stresses shift to the sides, or abutments, of the opening. Clearly, these compressive stresses around the opening exceed the pre-mining conditions. The problem of designing an underground opening, therefore, is to determine the maximum stresses and to note if they exceed the ultimate strength of the rock. Table 1 lists several rocks with their corresponding strengths. Figs. 3 to 5 depict the boundary stress concentrations around circular, ovaloidal, and rectangular openings. M is the ratio of the horizontal stress to the vertical stress, or as defined above, p/(l-p). This text will concentrate on the state of stress represented by M = 0.33, which corresponds to the condition of no lateral deformation in a rock having a Poisson's ratio of 0.25. For an ovaloid with an opening width-to-height ratio of 2.0 (Fig. 4), the boundary stress concentrations are at their maximum values at the comers of the opening, with values in excess of 3.0. If the depth of overburden is 500 ft, then the maximum boundary tangential stress ([ ] ) of the ovaloid is: [ ]

Jan 1, 1986

By Mann V. I

The Mount Isa property has been in operation since June, 1931; during this period operations have changed from the production and treatment of carbonate ores to the mining, milling, and smelting of sulphide ores. This change involved revision of ore-extraction methods.Stoping methods have been designed to apply to parallel lodes ranging from 10 ft. to over 100 ft. in width and dipping at 50° to 60°. The hardness and strength of the ore and enclosing wall rocks, together with the strength and thickness of the country rock between lodes, have permitted the selection of a sub-level stoping method for mining the sulphide ores.

Jan 1, 1938

Sulphuric acid leaching at atmospheric pressure of a number of Australian nickeliferous laterites was examined in detail. The results obtained indicate that nickel can be extracted from these ores, although the conditions required to achieve about 90 per cent extraction vary widely. These differences in reactivity can be related to the types of nickel-bearing minerals present.Nickel is more readily extracted from nickel-bearing clays such as chlorite, than it is from nickel-containing goethite.The results clearly show the problems associated with the processing of complex ores such as the nickeliferous laterites, and they indicate the need for complete characterization of each deposit.

Jan 1, 1978

By Misra V. N

Davis tube tests were conducted on a Koolanooka magnetite iron ore sample, supplied by Kingstream Steel Ltd, to determine the optimum grind size, maximum iron recovery and the cleanness of the products from low intensity magnetic separation (LIMS). The ore sample contained 38.6 per cent iron, 37.8 per cent silica, 6.5 per cent magnesia and 0.54 per cent alumina. XRD and microscopic examination showed that the main minerals in the ore were amphibole (42 per cent), magnetite (39 per cent), and quartz (14 per cent). Amphibole, (Mg, Ca, Fe),Si8O22.2(OH), containing 50.3 per cent SiO2, 35 per cent FeO and 11.5 per cent MgO is the main gangue mineral in the ore, and about 30 per cent of the total iron in the ore is contained in the amphibole. Heavy liquid separation tests showed that it is very difficult to separate iron from silica by gravity separation to obtain a high quality iron concentrate. Three grind sizes were initially tested, ie 45, 38 and 20 ¦m. It was found that grinding to 100 per cent -38 ¦m (P80 of 29 ¦m) appeared to be the best option for liberating the magnetite from gangue minerals. The iron recovery to the LIMS magnetic product for the 100 per cent -38 ¦m sample reached 73 per cent and the iron content was 65 per cent. Further test work suggested that the optimum grind size was a Psu of 25 ¦m.

Jan 1, 1999

By H. Yilmaz

A testing method for assessing the shear-bond strength of thin spray-on liner (TSL) on rock substrate was developed at Wits University Rock Mechanics Laboratories. The gap between a 20 mm thick steel ring and a rock core is filled with TSL along the depth of the ring. After the curing of the TSL for a predetermined period, the sample is placed on a base, which offers support to the steel ring and the TSL but not to the rock core. A compressive load is applied on the rock core displacing the core on TSL contact and punching it towards the void in the support base. Shear-bond strengths for different TSL products as well as shotcrete were measured. This paper describes the test set-up and points out the important aspects and procedures during sample preparation and test execution. The test results are also presented and discussed.

Jan 1, 2007

By Clyde Baker

Drilled shafts for many situations offer an economical alternative to driven piles. The Federal Highway Administration (FHWA) has spent considerable time and money in research and developing design and construction guidelines for drilled shafts. However, the full potential of the technology may not be realized because of the uncertainty of the effects of construction on the actual service behavior and the lack of either reliable quality control tests to check for or evaluate defects, or inexpensive load test procedures. Static load testing is very expensive and it is not feasible to load test each shaft on a project. Therefore, other means are necessary to confirm or evaluate the integrity of the completed drilled shaft or to determine the capacity of the completed shaft.

Jan 1, 1989

By W. P. Roux

Owing to decreasing high-grade ore reserves, there is a need for better understanding of the jigging process to improve the recovery efficiency of finer, lower grade material. The use of positron emission particle tracking (PEPT) was examined as a technique to study the motion of iron ore particles inside a laboratory batch jig. PEPT is a non-invasive method that can provide three-dimensional kinetic data on a particle in laboratory-scale processing units and has been successfully used to study mills, hydrocyclones, and flotation. Experiments were conducted to determine whether PEPT would be a viable technique to study iron ore jigging and what valuable information could be obtained. The results indicated that detailed information on the stratification rate of a particle could be obtained, with adequate resolution to track the particle?s movement through an individual jig pulse.

Jan 1, 2014

By Oliver Bowles

"Underground operation.In its broader sense the term ""mining"" is applied to all processes whereby raw materials are taken from the earth to be used as sources of mineral products. In a more restricted sense ""mining"" is applied to underground operations as contrasted with open pit work designated as quarrying. The tern is used in the restricted tense in this paper; for it relates to the exploitation of limestone deposits by modern methods of underground operation rather than by open pit methods.Present tendency toward miningIt may seem to some readers that a paper on mining limestone will find little general interest among lime plant operators, for only a limited number of them have yet resorted to this means of procuring raw materials. It is noteworthy, however, that a growing tendency exists toward underground operation, for one by one quarry owners are faced with increasing difficulties in open pit operation. It seems desirable, therefore, for operators to keep closely in touch with this gradual change in process, to inquire into the underlying causes, to compare costs, and to study the effects of the change in method on subsequent steps in calcining the stone to produce lime."

Mar 1, 1924

Disseminated gold mineralization in the Vunda River area 12 km SE of Lautoka in Viti Levu occurs sporadically in shoshonite volcanics within an alteration area of some 6 km2. No definite intrusions have yet been located though possible intrusions occur toward the centre and on the eastern margin of the area. The nature and distribution of alteration suggests the presence of a co-magmatic mineralizing stock just below the surface.The gold occurs within close spaced fractures and occasionally around the c1asts of breccia and agglomerate.Various types of alteration compatible with porphyry mineralization occur, but to date show no zoning or defined correlation with incidence of gold which occurs in various alteration facies.It is suggested that the gold and trace copper mineralization at Vunda arises from the sub-volcanic intrusive phase (monzonite) of the Sambeto shoshonite (5 m.y.) and is part of an E-W zone of porphyry-type mineralizationtrending easterly to the Kingston porphyry copper deposit at Navilawa.There is a close similarity between the Vunda mineralization and some of the porphyry deposits of alkali affinity in British Columbia, Canada.

Jan 1, 1978

By Dave Bigby

Hatworth Colliery, operated by RJB Mining (UK) Ltd, is successfully mining the Deep Soft Seam at a depth of 1000m using single face retreat longwalling. The seam is characterised by a weak roof generally comprising 4 to 6m of well bedded carbonaceous mudstones overlain by weak siltstones. The paper describes the layout and support design strategies which have enabled the colliery to adopt sole support by rock reinforcement techniques for its longwall gateroads. To achieve this success the colliery layout has had to be radically modified to take account of the in-situ horizontal stress field. The layout is also closely controlled by environmental considerations, the seam being one of the gassiest in the UK Economic support by strata reinforcement has been achieved using a combination of rockbolting of the roof and sides installed at the face of the heading, and systematic double birdcage cable bolting installed on drivage and supplemented ahead of the retreating panel. The layout and support strategies have been developed through a combination of detailed underground measurement of support and stress parameters backed up by numerical modelling using FLAC. The FLAC modelling has paid particular attention to careful representation of bedding properties and validation through underground stress measurement.

Jan 1, 1996

By T. P. R. de Jong, H. Harbeck

"This contribution reports recent mineral sorting experience and lists the opportunities of the newest generation of automatic sorters with a special focus on electromagnetic detection and Xray transmission. With the available sensor resolutions and actuator systems that are available today sorting of minerals down to 2 mm size and up to 250 mm lump size is technically feasible. In industry, ore as well as coal is still hand-picked and current automation potential only utilised in a handful of specific applications. Recently a number of technological developments took place that may increase sorting potential, save mill costs and lead to lower overall tonnage costs.They are:??High speed and high resolution sorting systems based on X-ray transmission imaging??High speed on-line image processing and further development of advanced data processing??Modular multi-sensor automatic sorting units (using one or more sensors such as colour, electromagnetic and X-ray in a single device)??Sensitive electromagnetic sensors for sorting based on differences in magnetic susceptibility and electric conductivityThe above enables compact dry separation, insensitive for moisture fluctuations and at high separation sharpness, as well as “electronic” high gradient magnetic separation for larger particles. Besides conventional X-ray transmission (XRT), dual-energy XRT (DE-XRT) is now being redesigned to meet the requirements of the mining industry. The mentioned technologies provide automatic dry separation of minerals and rock as alternative for conventional processing."

Jan 1, 2005

By W. J. Kroll

Jan 1, 1960

By Brown H. R, Wright E. A

The authors identify the workable coal seams, their distribution in relation to quality and economic occurrence and relate their analytical characteristics to industrial use. The development of established collieries is also discussed with regard to increased production demand.The authors also indicate the potential of the coal resources of the Southern District and postulate their ultimate development.INTRODUCTIONThe Southern Coalfield yields 30 per cent of the total production of bituminous coal in New South Wales. The economic potential of the coalfield was examined last by Harper (1915). Since that time additional knowledge has been gained by prospectors, mining companies and public authorities. Expansion in the steel industry and the building of power stations on the coalfields together with improvements in fuel technology, mining methops and road transport have resulted in production of coal from seams mice thoughtto have no economic value.DESCRIPTION OF THE COALFIELDFor the purpose of this paper the term Southern Coalfield includes also the South-Western Coalfield which together comprise the following Coal Districts:IllawarraDouglas ParkWollondilly-NattaiMoss Vale-Berrima (Hanlon, 1953).Geographically the coalfield is contained by the Illawarra Range in the east, the Shoalhaven River to the south, the Wollondilly River to the west, and in the north by a line...

Jan 1, 1958

Historically, the selection of mining sequence for multiple seam conditions has been based on many factors other than ground control considerations and minimization of interaction effects. Today, numerous operations are finding themselves mining above existing or abandoned operations, some of which exhibit large scale caving, pressure arches and subsidence troughs. Development of design criteria for the upper seam that would alleviate damage due to lower seam interaction effects can contribute substantially to the safety and productivity of many mining operations. The primary objective of this re search has been to identify methods of improving ground control conditions in the upper seam when mining through either passive or active subsidence waves. These methods concentrate on improved ground control practices for the upper seam, rather than reducing the amount of subsidence in the upper seams by improved practices in the lower seam. Design factors such as pillar size, pillar and opening orientation relative to the subsidence trough, offsetting intersections, and different support methods have been studied for the upper seam in a variety of typical geologic environments. Analysis has demonstrated criteria for ameliorating negative interaction effects and facillitating design in the superincumbent seam.

Jan 1, 1986

By Sanjeev Malhotra

The American Petroleum Institute (API) method of predicting pile capacities in sands is reviewed. Factors that influence pile capacity such as soil parameters, pile parameters, loading effects and installation effects are listed. In addition, the simultaneous occurrence of physical phenomena such as grain crushing, pile shaking, stress-redistribution and plugging add to the uncertainty in the prediction model. To better understand the method of prediction, each parameter and the associated uncertainty is revisited. It is evident that these factors are inter­related and sometimes compensating. This discussion also draws attention to the influence that pile installation procedures can have on pile capacities and highlights the need for field experience with various pile installation procedures for designers. In summary, the strength of the method lies in its simplicity and ease of application, but the possible savings generated by an improved method are too substantial to ignore.

Jan 1, 2000

By Bernhard Leist, William D. Leech, Johann Kröyer, Holger Evers

Landsvirkjun—the national electric power company of Iceland—is building the Kárahnjúkar Hydroelectric Project in eastern Iceland. Two glacial river systems will be dammed and channeled through a series of tunnels into a 690 MW underground powerhouse. The Project has a total of 73 km of tunnels to be excavated of which mosthave been completed. From three access adits, three large diameter (7.2 m to 7.6 m),main-beam, gripper-type, Tunnel Boring Machines (TBMs) are being used to complete50-km of the waterway tunnel. Using the TBMs was a first in Iceland to excavate the complex Icelandic basalt formations, which consist of inclined layers of hard basaltic flows with weaker scoriaceous and sedimentary interbeds. Faults, fissures and dykes that frequently cross the lava flows posed both geologic and hydrogeologic difficulties to the TBM tunneling. This paper describes the extreme challenges that the men and equipment had to endure to complete the tunneling, including the harsh winter weather on the surface and the cold, abundant ground water inflows within the tunnels.

Jan 1, 2007

By Shawna Munn, Jakub Hudler

This paper outlines the use of tunneling headwall softeyes for transit construction projects in the Greater Toronto Area (GTA) over the past decade. Due to spatial constraints, tunnel boring machines were used to construct the underground tunnels requiring the design of launch and exit shafts with headwall softeyes to facilitate tunneling operations. Variable ground conditions and shaft geometries lead to the development of innovative headwall and tunnel softeye design applications using fiber reinforced polymer (FRP) elements (beams, reinforcing bars, and tiebacks). This paper outlines the challenges and benefits associated with designing and constructing shafts using various systems. Lessons learned throughout design and construction of more than 20 structures over the past 10 years are outlined. The constructability challenges with using FRP and design performance are also discussed. For over a decade, the City of Toronto has been expanding its metropolitan transit network with a variety of new transit construction projects. Two recent projects in the Greater Toronto Area (GTA) for underground infrastructure include the Toronto York Spadina Subway Extension and the Eglinton Crosstown Light Rail Transit project. These add a total of 31 new stations and 18.6 km (11.5 miles) of underground transit (TTC 2017) (EllisDon 2016). Due to ground conditions and spatial constraints of existing surface infrastructure, these projects utilized tunnel boring machines (TBMs) to construct the underground tunnels requiring the design of various types of shafts and headwalls to facilitate underground tunneling operations. To allow for tunneling through the headwalls, these shafts were designed with “softeyes” - a section of the wall without metal reinforcement that allows the TBMs to tunnel through.

Jan 1, 2018

By J. A. Meech, R. J. Tucker

"A dynamic computer model has been developed to simulate the operation of ore crushing plants. The model was created in a general form to allow imitation of a wide variety of secondary crushing circuits with only minor program modifications. The system can be run on either a microcomputer or a large time-sharing main frame computer as required.The size reduction and separation characteristics of crushers and screens are based on standard manufacturers' design and performance data. These calculations are isolated within various subroutines to facilitate tailoring of the model to emulate any particular plant of interest. Input and output data are presented in a variety of formats. Crusher, screen and conveyor amperages and surge bin levels can be presented in a tabular form along with appropriate alarms arising from improper circuit operation or process interruptions. Graphical representation of the circuit together with strip chart data output are features of the system when operated in a microcomputer environment.The program is currently being used at Queen's University as a teaching aid to demonstrate plant operating characteristics, control strategies and design concepts. The acceptance of, and reaction to the program at this level indicates a good potential for it to provide a valuable tool for operator training."

Jan 1, 1985

By Ryan L. Veenstra

This paper presents a modelling study of a cemented paste backfill in an underground stope. The model was developed to help provide a better understanding of what is happening in the stope during the filling stage of the stope. In order to do this, the model incorporates the paste rise rate, stope geometry, and time-dependent input parameters. This paper looks at the effect of geometry in two parts. The first part compares a series of simple rectangular stope models. These models differ in size both in two and three dimensions. The second part compares the results of four 2D models together and then to the field instrumentation data. Part of this section introduces the geometry and instrumentation within the test stope.

Jun 1, 2012