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By Steven W. Hunt

"A paper called “Global Experience with Soft Ground and Weak Rock Tunneling under Very High Groundwater Heads” was presented at the North American Tunneling 2006 conference (Holzhäuser et.al 2006). It summarized global experience with earth pressure balance (EPB) and slurry shield tunneling on nine projects that encountered groundwater heads ranging from 6 to 11 bar. Since then, additional projects have been completed with groundwater heads ranging from 7 to 15 bar. Of these, the high pressure tunneling experience on the Lake Mead Intake No. 3 project in Nevada and on the Eurasia Tunnel (Istanbul Strait Crossing) had the greatest lengths of tunneling at face pressure over 7 bar. Experience with sustained pressurized face tunneling at groundwater heads over 7 bar and risk management observations are the focus of this paper. INTRODUCTION High groundwater head, particularly at 7 bar or more, is a major challenge when tunnelling in high permeability ground and on drives long enough to require cutter changes. It has a strong impact on design and operation of Tunnel Boring Machines (TBMs) in order to protect the main bearing from contamination, prevent excessive groundwater inflow, ensure face stability and enable access to the cutterhead and excavation chamber for maintenance. During the past 20 years, TBM manufacturers and suppliers have made tremendous improvements that allow tunneling at groundwater pressures to 17 bar or more. The most significant risk with high pressure tunneling is generally that of excavation chamber access and potentially the cutterhead for cutter changes, cutterhead repairs and TBM maintenance. Hyperbaric interventions are possible and safety variances have been approved for saturation dive interventions at pressures as high as 17 bar (Lake Mead Intake No. 3). While high pressure hyperbaric intervention equipment is available and safety approvals can be obtained at many locations, few contractors consider the cost and risk of hyperbaric interventions over 7 bar to be acceptable as the primary means of excavation chamber access. Experience with high pressure tunneling prior to 2006 was summarized in a paper entitled “Global Experience with Soft Ground and Weak Rock Tunneling under Very High Groundwater Heads” (Holzhäuser et.al 2006). That paper provided information on 9 projects: South Bay Ocean Outfall, San Diego; Channel Tunnel (French Side), France; Storebaelt Tunnel, Denmark; 4th Elbe Tunnel, Germany; Wesertunnel, Germany; Westerschelde Tunnel, Netherlands; St. Petersburg Red Line, Russia; Nara Prefecture Water Conveyance Tunnel, Japan; and Tokyo Wan Aqua Line Tunnel, Japan – see Table 1."

Jan 1, 2016

By Jones S. C

The problem of sealing a fluid serieite zone at a hole depth of 4000 ft was overcome by using a composite non-return valve plug and rod assembly which enabled cement to be forced under pressure into the zoneà

Jan 1, 1966

By Takashi Miyamoto, Hideo Nakae, Hideki Yamaura, Takeshi Yanagihara

"For the production of partially composed metal matrix composites, namely discontinuous MMCs, using a casting· process, the interpenetrated phase composites with SiC particles were fabricated by pressureless iDfiltration using molten Al-Si alloys. This process is based on a wetting phenomenon, therefore, we discussed the technique based on the reactive wetting. The SiC particles coated by diluted water glass were sintered in a mullite Tammann tube and simultaneously infiltrated with molten Al-Si alloys in air at 1173~1573K. As for the improvement of the wettability between the SiC and the liquid aluminum alloy, Fe3O 4 powder was mixed with the water glass due to the thermit reaction between Fe3O4 and molten aluminum alloy. In some experiments, pure aluminum powder was placed on the sintered SiC to increase the interfacial area and the chemical reaction between the sintered Sic. and the melt. By combining these conditions, we succeeded in the complete infiltration without pressure at 1173K.IntroductionAs is well known, the mechanical properties of metal matrix composites (abbreviated MMCs) are superior than that of ordinary metals. However, their use has not been widely accepted because the production cost is very high due to their poor machinability. Therefore, the production of partially composed, namely discontinuous MMCs, by as the Lanxide process [l,2] has been investigated for many years. The Lanxide process, it takes a long time, sometimes up to 10h, in a nitrogen atmosphere for the infiltration. Therefore, the cost will be higher for common use. On the other hand, a high 'pressure process has been adopted for the production of discontinuous MMCs by the Toyota Motor Corp.[3]."

Jan 1, 2000

By Takashi Miyamoto, Hideo Nakae, Hideki Yamaura, Takeshi Yanagihara

"For the production of partially composed metal matrix composites, namely discontinuous MMCs, using a casting· process, the interpenetrated phase composites with SiC particles were fabricated by pressureless iDfiltration using molten Al-Si alloys. This process is based on a wetting phenomenon, therefore, we discussed the technique based on the reactive wetting. The SiC particles coated by diluted water glass were sintered in a mullite Tammann tube and simultaneously infiltrated with molten Al-Si alloys in air at 1173~1573K. As for the improvement of the wettability between the SiC and the liquid aluminum alloy, Fe3O 4 powder was mixed with the water glass due to the thermit reaction between Fe3O4 and molten aluminum alloy. In some experiments, pure aluminum powder was placed on the sintered SiC to increase the interfacial area and the chemical reaction between the sintered Sic. and the melt. By combining these conditions, we succeeded in the complete infiltration without pressure at 1173K.IntroductionAs is well known, the mechanical properties of metal matrix composites (abbreviated MMCs) are superior than that of ordinary metals. However, their use has not been widely accepted because the production cost is very high due to their poor machinability. Therefore, the production of partially composed, namely discontinuous MMCs, by as the Lanxide process [l,2] has been investigated for many years. The Lanxide process, it takes a long time, sometimes up to 10h, in a nitrogen atmosphere for the infiltration. Therefore, the cost will be higher for common use. On the other hand, a high 'pressure process has been adopted for the production of discontinuous MMCs by the Toyota Motor Corp.[3]."

Jan 1, 2000

Die Suid-Afrikaanse Instituut vir Mynbou en Metallurgie het 'n paar jaar gelede 'n toekenning vir voortreflike akademiese prestasie deur vierdejaarstudente aan technikons ingestel. Disinvestment campaign by COLIN M.SPENCE As President of the Federation of Societies of Professional Engineers, which is an organization representing twelve institutions of the engineering profession comprising over 18 000 engineers of all kinds-of whom over 15 000 are either professional engineers or engineering graduates-I have been asked to make a statement on the disinvestment campaign on behalf of the profession.

Jan 1, 1985

A prize awarded by the SAIMM for outstanding academic achievement by 4th-year and 5th-year diplomates at technikons was instituted several years ago. The Senior Vice-President, Mr J.D. Austin, accompanied by the Institute's Secretary, Mrs D. Gardner, attended a prize-awarding function in the form of a luncheon at the Hotel School of the Technikon Witwatersrand on the 25th May.

Jan 1, 1984

By J. E. Hawley, R. C. Hart

"The Preston East Dome gold mine is in the southeastern part of Porcupine district, Ontario, 5 miles southeast of Timmins, and immediately south of the property of Dome Mines, Limited.The claims now owned by this Company were originally staked in 1909. After the property had remained dormant for many years, the present Company was organized in 1936 to resume development operations. Two shafts had been sunk: at the time of the early work on the claims, but lateral work from these failed to reach the ore deposits. A successful diamond drilling campaign undertaken under the direction of D. G. H. Wright, however, was followed by the sinking of a five-compartment shaft arid the erection of a mill. From the start of operations to the end of 1944, 1,292,000 tons of ore averaging $11.60 in gold a ton have been mined.An outstanding feature in this mine is the occurrence of the major gold deposits in quartz porphyry intrusives, though minor deposits are also found in the adjacent Keewatin volcanics. Most of the ore occurs in fractures, but the filling was accompanied by varying degrees of replacement of schistose wall-rocks. The ore deposits may be classified as:"

Jan 1, 1954

By C. L. Emery, A. V. Corlett

"The stress equilibrium is disturbed in a body of rock by a mine opening and is restored by a redistribution of the stresses around the opening. The pattern of the redistribution of unilateral stress around an opening has been established by mathematical analysis and photoelastic measurements. The pattern for multilateral stress is found by superimposition of unilateral fields. The mathematical analysts do not use the elastic moduli as parameters and they are not significant in photoelastic work. The medium is isotropic. The concept of unilateral stress from vertical loading and the classical pattern of its stress distribution around openings does not explain commonly observed failures around the perimeters of mine openings. They show evidence of compression where tension is postulated.When it is recognized that few minerals and perhaps no rocks are Hooke Solids, most rocks must be St. Venant Solids. The components have varying degrees of elasticity and viscosity. The assembly will be-have elastically to rupture under shock loading, but when loaded short of rupture will adjust viscously to equilibrium. Similarly, the highly elastic components may initiate rupture before equilibrium can be established when stress is instantaneously relieved. Polycrystalline adjustments may produce permanent deformation. The mechanics of consolidation, especially in sedimentary deposits, ac-quire a stress component normal to the direction of compaction which can exceed that of the loading. It is one source of prestress. There are others. The principles of prestress design are based on the normal beam reactions, modified by a built-in compression in the lower chord. When the beam is loaded to design limits, the lower chord retains some compression and the whole beam depth is effective in compression. Some of the . common evidences of failure in compression over a mine opening can be duplicated in a prestressed experimental model.When the triaxial stress pattern is recognized and suitable measuring techniques are devised, mine design can be done on a rational basis."

Jan 1, 1959

By W. Burr Bennett

The prestressed concrete industry in particular, and the precast concrete industry to some extent, are rank newcomers to the concrete construction field compared to the cement, ready-mixed or concrete masonry industries. This young industry reflects its youth and vigor in its enthusiasm, optimism and the belief that it can reach any goal it chooses to set -- and it is setting its sights high. The prestressed and precast concrete industry fully expects to become the major structural and architectural material by the 1980's. Before exploring how the industry expects to reach this goal, a brief look at the origins and the growth of the industry may be useful in an evaluation of the feasibility of this goal. It was always recognized that concrete, strong and efficient for supporting loads which cause compression, was weak and inefficient when used to carry loads which induce tension. Thus the reason for reinforced concrete in which the concrete efficiently carries the compression in a flexural member while low grade steel bars reinforce the concrete in the areas 'of tensile stress. (Fig. 1). The steel being relatively inexpensive, can passively, but quite effectively carry tensile force while the concrete carries compression. The concrete in contact with the reinforcing also protects the steel from corrosion and acts as insulation to provide a superior "built-in" fire resistance. The major disadvantage of reinforced concrete relative to its main competitor, steel, is its weight in relation to its load-carrying capacity. Reinforced concrete systems, such as waffle slabs, I-beams, thin shells, etc. ,

Jan 1, 1971

By David T. Swanson

The term "pressure tunnel" in the broad sense includes all hollow spaces, aligned along an axis and surrounded by rock, which are suitable for pressurization. In particular, this category includes: • horizontal or slightly inclined water pressure tunnels; • vertical or inclined pressure shafts; • pressure chambers or shafts of surge chambers; and, • compressed air storage tunnels. The main problems in the design and construction of pressure tunnels result less from their length or size than from the requirement for watertightness and, dependent upon this, reliability in operation and economy in construction. Where the lack of sufficient overburden does not permit the rock to accept the internal pressure in the tunnel, or where this pressure is so high that the watertightness is in doubt although the stability of the tunnel shell is not in question, a pressure tunnel must nevertheless be reinforced. Surge chambers, pressure tunnels and tailraces which are subjected to relatively low internal pressure, usually not much in excess of 1.5 MN/m2, are eminently suitable for construction in post-tensioned concrete. Pressure shafts, which as a consequence of the high water head are subject to a considerable maximum service pressure, are usually lined with a steel tube, a considerable proportion of the internal pressure being transmitted to the rock by backing concrete. TYPES OF LINING FOR PRESSURE TUNNELS In general, the type of lining will depend upon the nature of the rock. As a result, pressure tunnels usually are not uniform in con-

Jan 1, 1981

By Abhijit R. Sheth, Craig M. Benedict, John Brun, Ara G. Mouradian

"Amtrak recently replaced the 1907-era bascule two-track bridge over the Niantic River between East Lyme and Waterford, Connecticut. The project included new approach embankments, with approximately 2,500 lineal feet of retaining wall along the west approach and 780 lineal feet of retaining wall along the east approach. The paper focuses on the design and construction of the east approach retaining wall, whose alignment is directly adjacent to an existing wetland area which required protection. An anchored prestressed concrete sheet pile retaining wall was selected for the east approach. A combination of concrete anchor piles and ground anchors were used to support the wall. The design of the wall took into account two simultaneous train live loads, support of electric traction catenary structure foundations, and construction live load, while at the same time preventing permanent impacts to the adjacent wetlands. The design considered challenging subsurface conditions, shallow groundwater, the close proximity of the existing operating tracks, construction staging, and storm surge events in Long Island Sound.INTRODUCTION AND PROJECT HISTORYThe National Railroad Passenger Corporation (Amtrak) recently replaced the 1907-era bascule two-track bridge (No. 116.74) over the Niantic River, between East Lyme and Waterford, Connecticut, along the heavily-traveled Northeast Corridor (NEC). The two NEC tracks, which carry over 50 trains per day, run east-west over a narrow spit of land known as “The Bar”, which separates the Niantic River’s marine estuary to the north from the Niantic Bay to the south, before crossing the river. The bay is an arm of Long Island Sound and is occasionally subject to storm surge from hurricanes.The 1907 bridge was built as a replacement for the previous 1891-era swing-span bridge, and was constructed parallel to, and 49 feet north of, the swing-span structure. The two-track 1907 bridge consisted of a single-leaf bascule span and four approach spans supported on stone masonry piers and abutments. The new bridge increases horizontal navigational clearance for marine traffic in the river from 45 feet to 100 feet, and vertical clearance from 11.5 feet to 16 feet above mean high water with the bridge in closed position. The new bridge, constructed 58 feet south of the 1907 structure, features a single-leaf bascule span of 141.5 feet, with an approach span on either side."

Jan 1, 2017

By Denise C. R. Espinosa

Rechargeable lithium batteries are one of the most promISIng technology in battery development. Although Li ion batteries have been used as an alternative to the more polluting and less performing Ni-Cd batteries, Li ion batteries have limited life and their disposal is uncertain. It is imperative that valuables from wastes, such as lithium, should be recovered. The main objective of the present work was to characterize secondary lithium batteries for cellular phones. This was done using unit operations of mining processing, x-ray diffraction (XRD), chemical analyses and the rmogravimetric analysis (TG). The unit operations were hammer mill grinding, knife mill grinding, size separation and magnetic separation. After the hammer grinding process, the plastic cases were almost intact, however, they have released the cylindrical lithium batteries themselves and these parts correspond to 70% of the total battery weight.

Jan 1, 2001

By R. V. Fox, L. K. Sinclair, D. L. Baek

"In this study, rare earth elements were recovered from bastnasite concentrate and waste fluorescent lamp phosphors using supercritical carbon dioxide extraction with a nitric acid/tributyl phosphate adduct. Several pretreatment methods were used to alter the crystal structure of the source materials, and thus improve rare earth element recovery. Pretreatment methods included 1) dry roasting of the source material at 730oC, 2) decomposition with 50% sodium hydroxide solution at 150oC for 4 hours, and 3) decomposition with 12 M sulfuric acid at 300oC for 4 hours. Treated and untreated samples underwent supercritical extraction at 24 MPa and 65oC for 1 hour. Untreated bastnasite and phosphor samples showed <10% rare earth element recovery, but sodium hydroxide digestion resulted in >60% recovery for most rare earth elements. Dry roasting of the bastnasite concentrate was also effective, resulting in >60% recovery for cerium.INTRODUCTIONRare earth elements (REEs) consist of the 15 lanthanides, scandium, and yttrium. Scandium and yttrium are included because they are in the same group as lanthanum, appear in many of the same ore deposits as the rest of the lanthanides, and exhibit many similar chemical properties. REEs are used in a wide array of applications including electronics, magnets, catalysts, glass, and solid-state lighting (Xie, Zhang, Dreisinger, & Doyle, 2014). Because of China’s continued dominance of worldwide REE production, the United States Department of Energy has sought to diversify domestic supplies of REEs (United States Department of Energy, 2011). A key part of this strategy is the development of improved extraction methods for both ores and recycled sources.Supercritical fluid extraction (SFE) is a promising technology for extraction and separation of rare earth elements. Contact with an acid adduct dissolved in supercritical carbon dioxide allows for the rapid extraction of REEs from solid matrices. Supercritical CO2 has several potentially useful properties as a solvent, including high diffusivity and the ability to tune solvation properties by adjusting pressure. Such tunability may have applications in separating the REEs once they have been extracted from the solid phase. Tributyl phosphate/nitric acid adducts (TBP:HNO3) are a particularly promising class of adducts for SFE extraction of rare earth elements. Using TBP:HNO3 adducts in supercritical CO2, several researchers have successfully extracted REEs from their oxides (Wuhua, Pijia, & Yongjun, 2010; Zhu, Duan, Xu, & Zhu, 2009). However, there is a complication in applying this technique to many types of ores and recycled sources: REEs are often locked in refractory minerals which are resistant to acid attack, resulting in limited recovery in supercritical extraction."

Jan 1, 2016

By Sergio Romo, Gerardo Fuentes, Adriana Garcés

Refractory ores with gold entrapped in a sulfide matrix, must be processed in a first stage with chemical or physical treatment in order to liberate the gold for a subsequent step with cyanide. The goal of this research was to compare the refractory behavior of a gold concentrate treated using two pretreatment methods: pressure oxidation and fine grinding. Gold concentrate from Viacha Mining in Bolivia, assaying 50.11 gpt, with a P80 of 131 ?m was used. The concentrate contains arsenopyrite and pyrite as main sulphides in the matrix. A preliminary test with cyanide resulted only 13.5% of gold extraction with 4 hours of stirred leaching. Using an autoclave oxidation with sulphuric acid and 12 bar oxygen pressure at 220°C pretreatment, the cyanide gold extraction increased to 69.0% in 4 hours. When material was ground in a pulverizer, producing a P80 of 20 ?m and the product directly cyanided, stirred leaching gave a gold extraction of 65% in 4 hours. For both techniques, the effect of temperature, sulfur produced in autoclave oxidation, optimization of the cyanide and the nature of residues were also studied.

Jan 1, 2014

By S. A. Falconer

Much attention and publicity has been given, during recent years, to grinding, classification, flotation, and thickening. The various technical papers, and symposiums held to discuss these important phases of milling, have contributed to a better under- standing of the fundamental principles and operating variables involved. Another important part of milling- to the flotation operator-is a treatment step to which frequently too little attention is given-" conditioning," or the treatment the ground mineral pulp receives before it enters the flotation machines. Conditioning" is a hackneyed and frequently misused term, commonly employed to describe the pretreatment of surfaces of minerals in ore pulps or mill pr6ducts prior to froth flotation. In general, such pretreatment is for the purpose of changing the flotation characteristics of these mineral surfaces to enable them to respond in some desired predetermined manner when subjected to flotation. Taggartl states that the function of conditioning is "either to insure selective collector coating of one mineral species while another species is not; or to take such steps as will compensate for departure there from."

Jan 1, 1949

Conventionally, a combined system consist- ing of a dry or wet pulverizer and kneading mac- hine is applied to the pretreatment of fine mat- erials for agglomeration, especially for pellet- izing. However, treatment cannot be expected to be satisfactory owing to the complexities of the process. A new process was developed to over- come the defects inherent in the conventional process. This new process treats certain fine materials having a moisture content somewhat lower than that suitable for pelletizing in a ball or rod mill. The mill is of special de- sign in which grinding and strong kneading are performed to give an extremely homogeneous ball- ing material with appropriate size distribution and pelletizing characteristics. The most serious problem in this process is the choking of sticky materials in the mill. A specially designed rubber lining was installed in the mill to overcome this trouble. This paper presents actual results from our iron ore pelletizing plant relating to the pelletization of other fine materials.

Jan 1, 1974

By Yisa Liu, Lili Xu, Shina Li, Kang Li, Jiong Dong, Zichen Yin, Ruixin Ma

With the evolving landscape of gold mineral resource development and utilization, the easily treatable gold resources are continuously decreasing, while refractory gold minerals are becoming the most important resources in the field of gold extraction. In these original ores, most of the gold is encapsulated in the lattice of pyrite and arsenopyrite, resulting in difficulty of gold transfer into the solution during the leaching process. The most effective method to solve the problem of insufficient contact between gold particles and leaching reagent is oxidation pretreatment before leaching. Different from traditional high-temperature roasting, concentrated sulfuric acid was used as both an oxidant and leaching agent in a sulfideencapsulated refractory gold ore to decompose the pyrite in the curing environment to expose the gold and improve the leaching efficiency. The experimental results showed that under the conditions of liquid solid ratio 3:1, curing temperature 240 °C and the reaction time 1.5 h, the weight loss rate and iron removal rate of the ore sample reached the highest value of 60.01% and 99.68%, respectively. The main phase of curing residue was Fe2( SO4)3, and silica was nearly the only phase after washing. At the same time, by combining the sodium thiosulfate system gold leaching method, the gold leaching rate increased from 3.67% to 81.30% before and after pretreatment with concentrated sulfuric acid.

Feb 19, 2024

By Qing-hua Tian, Li-then Cheng, Xue-yi Guo

In order to recycle valuable metals from silver separated residue, a novel method using alkaline smelting at low temperature was proposed. The main factors affecting the main metal recovery such as the smelting temperature, smelting time, liquid-to-solid ratio and alkali addition were investigated comprehensively. The behavior of the main metal elements, such as Pb, Sn, Sb and Bi in silver separated residue was also discussed. The results indicated that amphoteric metals such as Pb and Sn can be smelted into the melt, while other metal elements, such as Sb and Bi were left in the residue.

Jan 1, 2011

By Corby G. Anderson

Hydrometallurgical technology for the pretreatment of refractory gold concentrates has been developed at Sunshine Mining and Refining Company. It employs a patented nitrous-sulfuric acid pressure leaching process which&apos; was proven industrially at the Sunshine refinery. Additionally, pretreatment for removal of antimony and some other impurities is done with alkaline sulfide leaching. This paper will discuss the successful application of these two technologies for pretreatment of a refractory gold concentrate prior to CIL gold recovery. A complex gold concentrate composed of pyrite, arsenopyrite and stibnite was tested. Results of antimony leaching in alkaline sulfide media will be discussed including some details of a novel and selective recovery method for gold leached by polysulfide or thiosulfate" Also, the factors important in and the results of the application of nitrogen species catalyzed pressure leaching to refractory gold concentrates will be detailed.

Jan 1, 1996

By E. Bauer, S. Moore

Technological advances in underground coal mining have led to a reduction in fatalities. This study demonstrated that the percentage of cumulative injuries remained largely unchanged across two decades of technological advances (1983-1984: 37%; 2003-2004: 33%). Furthermore, it was demonstrated that the average number of lost days due to cumulative injuries has increased (36±55 days and 62±82 days, respectively) which may have been due to the increased age of the work force or an increase in length of employment meaning that the mine workers injured in 2003-2004 had been exposed to ergonomic risk factors longer than those in 1983-1984. It is recommended that ergonomics processes be implemented as a means to systematically identify, prioritize, and resolve the root causes of these cumulative injuries.

Jan 1, 2007