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By Willard L. Hunter

The Bureau of Mines studied the effect of temperature upon the reduction of chromite by carbon and the relative reducibility of chromites as a function of their composition. Ferric oxide was also studied to provide comparative data. Pellets weighing approximately 1 gram and containing 70 percent ferric oxide, chromic oxide, or chromite and 30 percent graphite were subjected to closely controlled temperatures under a flow of argon for 15 minutes. The amount of CO and CO2 evolved was measured, and the reduced sample was analyzed by X-ray diffraction techniques. The reduction of Fe2O3 was studied over a temperature range of 600° to 1,400° C, while the reduction of Cr2O5 and chromite was conducted from 9000 to 1,621° C. The temperature above which appreciable reduction of Cr203 by graphite took place was 1,125° C. The temperature at which significant reduction started for three of the four chromite samples was approximately the same, indicating that there was concurrent reduction of iron and chromium oxides in the chromite mineral rather than selective reduction of iron oxides followed by reduction of chromic oxide. Rhodesian chromite appeared to dissociate at a lower temperature with concurrent reduction of iron. Based on the temperature at Which chromite was 50 percent reduced in 15 minutes, Transvaal chromite reduced most easily, followed by Mouat, then by Kampersian, and finally by Rhodesian DFC material. Statistical analysis of test results indicated that the ferric iron content of chromites affects their reduction behavior more than any other constituent.

Jan 1, 1966

By Anselmo Monteiro Ilkiu

No presente trabalho será apresentado um modelo matemático para a análise da instabilidade plástica de um cilindro de parede fina sujeita a pressão interna, considerando o material com anisotropia normal R no estado plano de tensões. As equações foram obtidas, com base nas teorias elásticas e plásticas, considerando o critério de escoamento de von Mises no estado plano de tensões em termos da anisotropia normal, e de acordo com os trabalhos realizados por Johnson & Mellor [1], Chakrabarty [2] e Al-Qureshi [3].

Aug 16, 2017

Dynamic permeability is a significant hydrologic condition associated with in-situ leaching at the Cyprus Casa Grande operations. Several factors contribute to changes in the permeability conditions. They are: 1) hydraulically induced fracture development, 2) geochemical changes during leaching in the rock matrix, and 3) changes in the relative degree of saturation of the deposit. Dynamic permeability conditions were evaluated using available pressure and flow rates from the 58 injection and recovery wells obtained over one year period. A finite element, 2-D hydrologic model called INVERT which is designed to estimate aquifer parameters under transient and steady state flow conditions was used for the investigation. The permeability conditions during 7 different steady state intervals throughout the one year time frame were determined. The results confirm that big changes in permeability occur as a function of time as well as a function of injection pressure condition.

Jan 1, 1991

By Alfred L. Ransome

The consumption of slab zinc in the United States increased sevenfold in less than a half century since 1900. Therein is reflected the innate characteristics of this versatile and nearly indispensable nonferrous metal whose use has grown at more than twice the rate of industrial production. The total metal consumption was substantially stimulated during the two World War periods, which were likewise marked by notable changes in use pattern accompanied by shifts in geographic distribution. This information circular summarizes basic data collected for many years by the Bureau of Mines, but in particular presents for the 1940-45 period details derived from the comprehensive slab zinc consumption survey inaugurated in 1940. The total consumption of slab zinc has been broken down into four major categories galvanizing, brass products, rolled zinc, and zinc-base alloys -- with minor applications grouped under a fifth heading, other uses. Ex- cept for the inclusion of zinc-base alloys with other uses before 1926, the above-named segregation has been shown for the entire period 1900-45. 11- though a substantial tonnage was taken by all groups in all years, there were large shifts in the use pattern in both World War periods. In both, the Allied Powers depended heavily on the United States for zinc-bearing products, especially those required by war industrius. The departures from usual uses were, however, much more marked during the second than in the first period, mainly because the United States could not have met the tro- mendously expanded war-materiel demands had the greater slab zinc needs of a period of high industrial activity been supplied. The geography of consumption is known in detail only for 1940-45. Even in that short period, substantial shifts are observable, largely the reaction from conversion to war production in 1940-41 and reconversion to peacetime consumption in 1945. However, there is so evidence of other shifts in consumption centers that appear to reflect longer-term develop- ments.

Feb 1, 1948

By M. Bryson, J. Taguta

The Prieska deposit, mined between 1971 and 1991, is one of the world’s top thirty volcanogenic massive sulphide (VMS) base metal deposits. The Prieska Copper Mine in the Northern Cape Province was closed by Anglovaal when underground mining had extended to depths which did not allow for safe and economic extraction of the deposit at the time. The mine has a recorded historical production of over 1 Mt of zinc and 430 k tonnes of copper from 46.8 Mt of milled sulphide ore, achieving life-ofmine metal recoveries of 85% for copper and 84% for zinc into high quality concentrates (refer ORN ASX release 15 Nov 2019). Orion Minerals Ltd is currently investigating the feasibility of developing a new mine in the footprint of the historical Prieska Copper Mine, using the extensive remaining infrastructure, with the intent of extracting the unmined zinc-copper mineralisation from the Prieska deposit. This paper reports results on the flowsheet development philosophy on the hypogene ore, and challenges encountered in the process. This study initially failed to replicate historic copper and zinc recoveries employing the historic production flowsheet and reagent conditions unmodified on bench scale, as the copper and zinc were co-floating. Flowsheet modifications were therefore made to improve differential flotation and recovery, resulting in achieving comparable saleable products and recoveries from processing the hypogene ore on bench scale. Flotation variability test work on the hypogene ore focused on the use of the original flotation procedure and reagent suite using a sodium cyanide-zinc sulphate depressant system on the copper circuit, and it generated a saleable copper product of 20-26% Cu grade at 80-86% recovery. The zinc circuit generated a saleable zinc product grading at 48-55% Zn at 80-94% recoveries. Some zinc losses were due to the deportment of some zinc in sauconite. It is recommended that further test work may further improve the copper grades and recoveries. Keywords: Prieska, flotation, hypogene ore, flowsheet development, sulphide flotation, reagents

Jan 1, 2020

By A L. de Ambrosis, F M. Weir, M Fowler

Traditional kinematic and statistical analyses of geological structure for geotechnical engineering applications, while considered industry standard practice, have some limitations and unrealistic assumptions. An improved approach involves a discrete fracture network (DFN), a numerical model that explicitly represents how defects may be spatially distributed through the rock mass. The DFN technique utilises the structural data in stochastic analyses to give a range of possible models used for visualisation and stability analyses.The early development of the DFN approach was largely associated with modelling fractured hydrocarbon reservoirs and nuclear waste isolation programs. With recent improvements to computational power it has become recognised internationally as a valuable tool for modelling some geomechanical problems encountered when designing excavations in fractured rock masses. For tunnelling or slope stability projects DFN modelling provides visualisation of a rock mass and identification of likely failure mechanisms.This paper presents a suite of DFN modelling undertaken for the design of a tunnel within the Ashfield Shale unit of the Sydney Basin, Australia. The necessary input parameters and derivation of these, along with the importance of both an accurate engineering geology model and validation of the synthetic fracture network are demonstrated. Multiple realisations of the DFN were analysed to provide an indication of the number and volume of unstable blocks for the proposed tunnel geometry, enhancing support design. One fracture network realisation was sliced along multiple sections for use in finite element modelling.CITATION:Weir, F M, de Ambrosis, A L and Fowler, M, 2014. Discrete fracture network modelling for tunnel design in the Sydney Basin, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 219–226 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By W. M. Cross

The hydrophobic character of sapphire surfaces in SDS solutions was examined with respect to the aggregative nature of the adsorbed surfactant phase. It was found that, at equilibrium, sapphire surfaces having adsorbed SDS bi-layers exhibited no contact angle. Conversely, when the adsorbed SDS was found to be mi-cellar in nature, sapphire surfaces developed significant hydrophobic character. The surface states as detected by Fr -IRIIRS conformational analysis were found to be reversible with temperature. The variation in adsorption density with temperature was studied by in situ Fr-IRIIRS. The isosteric heat of adsorption was calculated to be -1.6 kcal/mole. Although the adsorbed SDS was found to undergo a reversible phase change between 25 and 32°C, similar to SDS in solution, the extent of adsorption was not reversible with temperature.

Jan 1, 1993

By Carl Erickson

The term shortwall mining is somewhat of a mis¬nomer. It may infer a longwall mining system, but of much shorter face length. Actually, continuous pillar mining is a more descriptive term. Coal is mined using a continuous miner as would be done in pillar extrac¬tion, but with the addition of roof supports to control the caving. Face length on such a system typically is 46 to 61 m (150 to 200 ft). The coal is cut in front of the roof supports in the same direction as with a long¬wall shearing machine or plow, but it is mined with a continuous miner and shuttle cars of the same type as used in continuous mining. ROOF SUPPORTS Roof supports for shortwall mining must be con¬siderably larger than those used for longwall mining because of the additional roof to be supported by the wider 2.6- to 3.4-m (81/2- to 11-ft) cut of the continuous miner. Capacities of shortwall chocks in current use vary from about 454 to 726 t (500 to 800 st). The higher capacity as compared to longwall roof supports is needed primarily because of (1) the greater support length, hence more roof weight, and (2) the presence of draw slate in the eastern coal seams, where shortwall is being used. The most popular shortwall support currently used is the four-leg 590 t (650 st) model. This support is shown in Fig. 1. The price of this support is approxi¬mately $25,000 each. As shown in Fig. 1, the shortwall chock incorporates an unusually long forward bar that has an additional hydraulically operated extension bar to provide face support for the wide miner cut. METHOD OF OPERATION Mining Sequence In shortwall mining, two or three (depending upon the chock design) move up cycles of the chock are needed because of the miner cut width. Fig. 2 depicts the five steps required to complete the move of chock and spill plate using a miner that takes a 3.3-m (10-ft,

Jan 1, 1982

By Eckley B. Coxe

I wish to call the attention of the Institute to a peculiar variety of anthracite which occurs in the Buck Mountain vein at our collieries at Drifton, and in the same and other veins in different localities in the anthracite coal-fields. It is known among the workmen as iron-gray or cast-iron. It has a dull, greasy appearance, as if a piece of ordinary anthracite had been rubbed with a dirty and greasy rag and allowed to dry. It was formerly considered a very impure coal containing a high percentage of ash, and was picked out of the coal and thrown away. But the following analysis of it and of its ash, made by Mr. J. Blodget Britton, of Philadelphia, shows that such is not the case, the percentage of ash not being much higher than that of the ordinary anthracites as they are prepared for market. ANALYSIS OF COAL. Water,.........4.36 Fixed carbon, by difference,.. 84.90 Volatile combustible matter,. . 3 48 Ash,..........7.26 100.00 The carbon proved to some extent to be of the nature of graphite, and slowly combustible. ANALYSIS OF ASH. Silica,.........25.66 Sulphur,........ .17 Alumina,........27.03 Phosphoric acid,.......21 Ferric oxide,.......42.83 Alkali, undetermined matter and Lime,.........1.56 loss,.........60 Magnesia,........1.83 Manganous oxide,......11 100.00 We recently collected a quantity of the substance and made a fire with it, in an ordinary stove, which was kept up several days. We found that it burned with intense heat, and apparently as freely as our other coal does. Mr. Britton is probably right in his view, that the difference in appearance is not due to impurities in the coal, but to the fact that the carbon is in a more or less graphitic form, as many of the standard coals are no purer. I bring this before the Institute as I know that a large quantity of this valuable fuel is thrown away every year, on account of its supposed impurities.

Jan 1, 1879

By Donald W. Scott

Chemical thermodynamic properties for the ideal gas state from 0 to 1500 K are tabulated for all of the alkane hydrocarbons through C10. These properties are based on correlations of the extant data for the entropy, vapor heat capacity, and enthalpy of formation of individual alkanes and the equilibrium constants of alkane isomerization reactions.

Jan 1, 1974

By Alan R. Buehler

The Bureau of Mines conducted a mineral investigation of the 10,500-hectare Cache Peak study area in 1992; the area had been proposed as wilderness. Bureau personnel examined and sampled prospect workings; 14 rock and 20 placer samples were taken during the investigation. The study area is centered about 40 km south-southeast of Burley. Idaho, in the Sawtooth National Forest. There were seven mining claims located inside the study area, and one additional historical mining claim location. Gold, silver, copper, lead, zinc: Possible resource, poor exposure precludes estimate. Marble: Several million tonnes may be suitable for a variety of uses; markets too distant to favor mining. Sand and Gravel: Several million m3, but markets and transportation costs do not favor mining. Quartzite: Several million tonnes may be suitable for metallurgical purposes; however, markets are too limited to mine. Slabs have been quarried at three localities adjacent to the study area, for decorative stone. Production: In 1979, two tonnes of ore were produced and a plan of operations was submitted calling for approximately 5 km of access road for the Last Chance mine. Decorative stone production was not recorded.

Jan 1, 1993

By K. Turgeon, D. Larivière, L. Whitty-Léveillé, J. -F. Boulanger, C. Bazin

"The processing of ore containing rare earth elements leads to the production of an impure solution of these elements. The separation of the rare earths from the impurities and the production of individual elements is usually carried out by solvent extraction. The effectiveness of the extraction conditions and of the reagents is generally tested in the laboratory. This paper deals with the processing of results from solvent extraction laboratory tests planned to generate data redundancy. A method is proposed to take advantage of the data redundancy by accounting for the pH variation during the extraction. The parallel processing of several tests also allows estimating the equilibrium constants for the extraction. The proposed method produces equilibrium constants that are more reproducible than values estimated using conventional approaches. The method is illustrated with solvent extraction tests conducted on synthetic solutions of rare earth elements.INTRODUCTIONThe processing of ores containing rare earth elements (REE) usually includes the production of a concentrate of the minerals carrying the REE. These minerals, for instance monazite and bastnäsite, contain the 14 elements from La to Lu plus yttrium and scandium. As an example monazite has the general formula of (La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy…Lu)PO4 with a typical lanthanum content of 20-26%, cerium content of 40-50%, praseodymium of 4-6%, neodymium of 16 to 20%, and decreasing concentrations of heavier elements (Gupta & Krishnamurthy, 2005). During the processing of a REE mineral, it is generally not possible to isolate and separate a single REE from all the rest. The mineral molecules need to be broken (usually via a heat treatment followed by leaching with a base and/or an acid) to produce an aqueous solution of the REE of the ore. After purification of the solution, the REE can be precipitated as a bulk concentrate and sold to a refinery that separates the REE into particular groups of REE such as the light versus heavy REE or into individual elements such as lanthanum, neodymium, or europium oxides to yield value-added products."

Jan 1, 2016

By S. Banisi, A. Haji-Zadeh, A. R. Hasankhoei, M. Maleki-Moghaddam

At the concentration plant of the Gol-E-Gohar Iron Ore Company (Iran) three 9m × 2.05m AG (Autogenous) mills (fixed speed) are used in parallel in a dry operation. The test works conducted in a scale down mill with a diameter of 1m indicated that conventionally used "deflector" type liners did not provide efficient environment for grinding. In this research, to improve the grinding efficiency, a new design using low profile end liners incorporating radial ribs of proper height was investigated. In order to determine an appropriate liner design at different operating conditions, a 100cm×10.8cm model mill was used for experimentation. The special design of model mill made it possible to increase the radial ribs height in steps of 6mm up to 18.5mm. The transparent end of the mill enabled accurate trajectory determination by image analysis. The results indicated that the new lower height profile deflectors and 15.5mm-height (14.5cm in industrial scale) radial ribs improved the mill performance while avoiding excessive pressure drop across the mill and wear on the liner. The image analysis showed that the use of new liners increased the distribution of coarse particles across the mill cross section from 28% to 35%. A new liner design was proposed by decreasing the number of liners in each slice from 5 to 4 pieces. The thickness of the inner head liners reduced from 45cm to 30cm and the outer deflector liners replaced by radial ribs. The distance between the feed and discharge inner head liners increased from the original 115cm to 145cm which increased the effective length of the mill by 26%. The new design reduced the weight and volume of end liners by 9% and 23%, respectively. It was predicted that the new liners design increases the mill throughput by 10% and reduces the metal consumption by 20%.

Jan 1, 2016

By Maryam Ghodrat, Bijan Samali

Disposal of waste syringes in a safe and eco-friendly way has been an issue of considerable scale for decades. The generated amount of waste syringes has escalated with the rapid growth in population and wide acceptance towards single-use medical devices. Some hospitals have their own on-site incinerators ,but recent tightening of air quality regulations and landfill levies led to the closure of manyon-site incinerators. The solution to this problem implicates the development of an environmentally-sound method that would employ these waste materials. This work investigates a thermodynamic modelling approach for incineration treatment of waste plastic syringes in Electric Arc Furnace (EAF) steelmaking. Mass balance was obtained from HSC Chemistry thermochemical package. The results indicate that the rate of iron oxide reduction in the slag is higher when coke is partially replaced by waste plastic syringes. Furthermore, the amount of dust and stack gas emission was reduced by around 0.4% and 1.25% respectively by replacing 20%-weight of pure coke with waste plastic syringes. The study demonstrates part of the coke can be successfully replaced by waste plastic syringes in electric arc furnace to provide additional energy from combustion without affecting the main process.

Mar 1, 2018

By Z. T. Bieniawski, R. K. Zipf

"Zipf Jr., R.K. and Bieniawski; Z.T., 1989. A fundamental study of respirable dust generation in coal. Min. Sci. Technol., 9: 87-99Black lung disease in coal miners induced by the formation of fine fragments of coal imposes very high human and direct costs. A fundamental understanding of the fracture processes leading to fine-fragment formation in coal by applying principles of fracture mechanics is presented. A four-step hypothesis is proposed which sequentially describes the mechanics of fine-fragment formation during a generic coal material—coal cutting tool interaction. These steps include: (1) development of a crush zone under the tool tip, (2) macrocrack propagation. (3) shear movement along macrocracks, and (4) additional fragmentation from shear. This model contains two sources of fine fragments, namely crushing under the tool tip and shearing along the macrocrack surfaces. Three critical assumptions are made that require experimentation. First, the coal material must contain flaws of sufficient density and sufficiently small size to liberate fine fragments by crushing. The following conceptual relationships are proposed between flaw size, spacing and fragmentation: first, the active flaw size must be less than the desired particle size and second, the spacing (or density) must be in the order of the particle size. The second major assumption is that a mixed mode fracture theory will describe the initiation and crack growth direction for the microscopic inherent flaws. The third assumption is that some degree of roughness damage, and interlocking exist along the newly formed macrocrack surfaces such that a small amount of shear movement along that surface leads to additional particle formation at a microscopic scale. Preliminary analysis of the mechanical regime under a cutting tool tip places order of magnitude bounds on the stresses strains, cycle time, stress rates and strain rates. Even though the tool moves and loads the coal material with considerable speed, a quasi-static stress analysis is applicable in this region.Introduction.The generation of fine fragments (respirable dust) during various coal mining processes may lead to the incidence of coal workers pneumoconiosis (black lung disease). The human and direct cost of dust-induced illnesses in coal miners is very large. By several. accounts [1,2] the Federal Government paid out about $12 billion to almost 500,000 coal miners and their beneficiaries between 1970 and 1980. In addition, several states and many coal operators have established their own compensation programs at costs ranging from a few cents to several dollars per ton of coal mined [2]. Since 1980, 'the present liability of the Federal disability trust fund has approached $20 billion and the benefit payments exceed $1 billion per year. There .are also hidden costs due to dust, in the form of increased equipment wear and decreased operator productivity, both of which are due to the poor operating environment. Quantifying these costs may be difficult; however, they may be in the same range as the present pneumoconiosis costs. These high human and direct dollar costs may be prevented or reduced through long term research efforts directed at understanding the generation and control of respirable dust and the incidence of black lung disease."

Jan 1, 1989

By Katarína Gáborová, Marcela Achimovičová, María Florencia Márquez‑Zavalía, Jaroslav Briančin, Oľga Šestinová, Pavel Škácha

In this paper, the structure, morphology, chemical composition and leaching of naumannite ( Ag2Se) were studied. Mechanical activation of Ag2Se in a planetary ball mill resulted in increasing its specific surface area. The influence of milling time on the particle size was studied by particle size distribution analysis and scanning electron microscopy. The leaching kinetics of non-activated and mechanically activated samples in 3.5–7.9 mol/L HNO3 solutions were examined. Subsequently, the effect of leaching temperature in the range of 25–50°C on the recovery of silver from mechanically activated naumannite was documented. The maximum yield of silver 94% was achieved after 120 min of leaching in 7.9 mol/L HNO3 at 50°C for the sample mechanically activated for 30 min. Based on calculated activation energy values from the Arrhenius equation, a mixed leaching mechanism consisting of diffusion and surface chemical reaction as the rate-controlling steps of the solidliquid reaction was assessed.

Mar 4, 2023

By Harold L. Lovell

Problems associated with fines (minus 6 mm, 1/4-inch) production, preparation, and utilization have long plagued the coal industry and are now more acute than ever. Continuous deep mining systems create more fines which have moisture; content greater than natural levels from dust control spraying and often add substantial levels of mineral matter due to mining selectivity constraints. Frequently, during preparation, more -fines are developed to achieve improved component liberation. Coal consumers often specify small sizes whether for carbonization, combustion, or conversion. Wet beneficiation systems process fines by several' types of unit operations, but usually must also incorporate costly and complex dewatering systems to reduce the moisture content of the products. Existing pneumatic preparation systems are constrained between product equality and yield by the sharpness of separation. These limitations become more severe with decreasing particle size and increasing feed moisture content. Control of particulate emissions, both process and fugitive, during pneumatic preparation, can be forbidding. A pneumatic preparation-process which would overcome these constraints, could be most enticing. The DryFlo system is being evaluated to quantify performance characteristics as regards these constraints.

Jan 1, 1976

By V

"Recent regulations, as well as a general aversion to central dust collectors within the Powder River Basin Coal user’s community, have created a need for an alternate method for eliminating airborne dust. This paper addresses the capital expenditure as well as the cost of ownership of an integrated point source air cleaning system in comparison to a central collection system. This assessment was conducted by comparing the cost to purchase and operate a central dust collection system and integrated air cleaner system on a typical multiple transfer point application. The central dust collector consists of a negative pressure blower, a series of filter bags, a collection hopper, a screw conveyor to place collected material back into the material stream, and a series of ducts to pull air and dust from individual pickup points. The point specific integrated air cleaners consists of a negative pressure blower to pull dust and air from an application point through a bag-less filter media located at the application point. The agglomerated material is then redeposited into the material stream at point of use without the need for ducting or a central material hopper. The assessment yielded a 54% reduction in capital expenditure and a 26% reduction in operating costs for the same application when using individual dust filters as opposed to a central system. In addition to the lowered cost, there are reductions in risk associated with the elimination of ductwork and the central containment enclosure for collected explosive dust. By the conclusion of this paper, the reader will have a better understanding of the quantifiable differences between a central dust collection system and a set integrated air cleaner systems. BACKGROUND Spillage has always been a problem in the bulk solids handling industry. As long as there have been conveyors, there has been spillage. Spillage is material that falls off a conveyor belt and creates a hazard in the environment around a conveyor belt."

Jan 1, 2016

By J. S. Lee, R. K. Massarsch

"A 3.2 km long immersed road tunnel forms part of the Busan-Geoje Fixed Link in South Korea, which connects Korea's second largest city Busan, with the island of Geoje. To ensure the water tightness of the joints of the segmental tunnel structure and to limit the forces in the shear keys, the differential settlements have to be limited. This was achieved by extensive soil improvement of the marine clay below the tunnel with cement deep mixing (CDM) and sand compaction piles (SCP). This paper focuses on the characteristics of the marine clay, the basic design principles, layout and constructional issues of the CDM soil improvement, and numerical and numerical analyses to predict settlement and stability.INTRODUCTIONThe Busan-Geoje Fixed Link consists of two short cut & cover tunnel access ramps, a 3.2 km long immersed tunnel (Figure 1) and two long span cable stayed bridges. The tunnel consists of eighteen concrete elements each of 180 m length having a rectangular cross section of 26.5 m in width and 10 m in height. The tunnel elements are cast in a dry dock on shore and floated out to the sea, immersed in their final positions on a gravel bed in pre-excavated trench and connected to each other by a dual gasket system. The water depth was up to 50 m making the tunnel of the deepest yet constructed. After immersion, the tunnel is protected by backfill material at the sides and rock armour on top. Each tunnel element consists of eight 22.5 m long segments. The joints between the segments and between the tunnel elements are equipped with EDPM water stops, Omega seals and concrete shear keys. The longitudinal displacement behaviour of the segmental tunnel structure in the varying ground conditions represents a complex soil-structure interaction problem which has been modelled with a FEM structural model representing the tunnel, the joints and with springs to represent the soil that are derived from the PLAXIS soil/foundation models. In order to ensure the water tightness of the joints which have limited opening capacity and to limit the forces in the shear keys, differential longitudinal settlements have to be limited. This is achieved by limiting the variations in subgrade modulus along the alignment and it in practice means that differential settlements are limited to a few tens of millimetres. Without soil improvement of the marine clay below the tunnel, long-term tunnel settlements of up to 400 mm were predicted when taking into account the likely variations in the trench profile, backfilling and uncertainties in the soil properties. Such large total settlements led to large variations in the sub-grade reaction along the alignment, which in turn resulted in significant differential settlements, unacceptable joint opening and large shear key loading. It was therefore decided to carry out extensive soil improvement with cement deep mixing (CDM) (CDIT, 1999) and sand compaction piles (SCP) (Kitazume, 2005) after studying a number of foundation alternatives."

Jan 1, 2015

By Li Shibo, C. Halls

The compositions of olivine, pyroxene and chromite from the Proterozoic ultramafic complex are analagous to those of cumulate ultramafic rocks of tholeiitic origin, suggesting that the parent magma may have been tholeiitic rather than komatiitic. The complex contains economically significant Ni-Cu sulphide mineralisation. The high sulphide/silicate ratio is best explained in terms of the segregation of sulphides from a large volume of magma, of which all but the ultramafic cumulate fraction has since been eroded. Platinum-group minerals that have been identified include sperrylite, moncheite, native platinum, froodite, merenskyite, michenerite and Pd-rich pentlandite lamellae exsolved from pyrrhotite. They are characteristically found in close association with chalcopyrite, either along the contacts between hydrosilicate and sulphide grains or in cracks within pentlandite and chalcopyrite, which may also be intergrown with galena. Crystallisation from a Cu-rich residual magmatic liquid also enriched in Pt, Pd, As, Sb, Bi, Te, Zn and Pb is postulated.

Jan 12, 1993