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The pressure of low commodity prices forced the design process for the second lift of Northparkes E26 Mine to adopt a continuous improvement philosophy. The emphasis was to minimise capital expenditure while still maintaining the excellent low operating costs achieved on Lift 1. Although the first block cave lift at Northparkes is the most productive underground mine in the world and is held up as a benchmark for the use of technology in mining, areas for improvement were identified. Every area was critically assessed and investigated for the possible application of new techniques and technologies. Key learnings from the construction and production phases of Lift 1 were captured, documented and used as the starting point for the Lift 2 design. This paper shows how and why the design parameters initially used onLift 1 were changed to become the current E26 Lift 2 developmentproposal. The main differences between the two block caves arehighlighted. The alternative techniques and equipment that wereconsidered are also discussed. * Originally published in the Proceedings of MassMin 2000,published by The AusIMM.

Jan 1, 2001

By J. B. Clemmer

This report summarizes the results of u laboratory study of the beneficiation of Arkansas bauxite by flotation. Although the investigation is not yet completed, a preliminary retort of the results on several typical bauxites is presented to show the merits rind limitations of flotation for the production of concentrates acceptable to the aluminum industry. It is

Jan 1, 1941

By Robert A. Rapp, Ronald L. Pastorek

Solid-state electrochemical measurements by three alternative experimental procedures were made with the cell FeO, Fe3O4 |Zro.85Cao.15O1.85 |Cu| Zr0.85CaO.15O1.85 | FeO, Fe304 to establish the solubility and diffusivity of oxygen in solid copper in the temperature range 800" to 1030°C. The solubility of oxygen in solid copper and the diflusivity of oxygen in solid copper Dgu = 1.7 X 10-2 exp(-16,000/RT) Cm2/sec were determined and confirmed in alternative experiments. The enthalpy of solution of oxygen in solid copper equals —10,000 cal per mole; the partial excess entropy of the oxygen atoms in the Cu-O dilute solution is approximately the same as that found for interstitial atoms in other metals. The diffusivity of oxygen in solid copper is consistent with that expected for an interstitial atom. RELIABLE values for the saturation solubility N(s) and diffusivity DO of oxygen in solid copper have not been unambiguously established in the literature. Following three early determinations by others,1"3 Rhines and Mathewson4 reported that the solubility of oxygen in solid copper increased from 0.007 at. pct 0 at 600°C to about 0.015 pct at 1050°C. Phillips and skinner,, using essentiially the same analytical procedure, reported that the solid solubility increases from 0.0018 at. pct 0 at 550°C to about 0.0075 pct at 1050OC. The only previous value for the diffusivity of oxygen in solid copper was reported by Ransley.6 Ransley deoxidized Cu-Cu2O alloys in an atmosphere of carbon monoxide gas to yield a solubility-diffusivity product. He used the solubility data of Rhines and Mathewson to calculate the diffusivity values. Another method for obtaining the solubility-diffusivity product (N(s) DO) is by measuring the widths of internal-oxidation zones in copper alloys as reported by Verfurth and Rapp.7 However, the calculated N(S)Do products depend upon the alloy content of the specimen, so that the internal oxidation of copper alloys does not follow ideal internal oxidation kinetics. As a result, unequivocal values for the N(s) DO product were not obtained by this procedure. A solid-state coulometric titration technique similar to that employed in this work was introduced by C. Wagner8 to study the dependence on silver activity of the Ag/S ratio in silver sulfide in the temperature range of 160" to 300°C. Similar experiments have been carried out by C. Wagner and co-workers9-11 to study the stoichiometry range of silver and copper tellurides, cuprous sulfide, and cuprous selenide. Numerous authors have carried out electrochemical measurements with a solid oxygen-ion-conducting electrolyte to determine the solubility and/or diffusivity of dissolved oxygen in several liquid metals.12-l6 Rickert and Steiner17,18 have used solid-state electrochemical measurements to determine the diffusivity of oxygen in solid silver from 760" to 900°C. Two different cell geometries were used. In the cell of linear geometry Fe, FeO | ZrO2 + (CaO) | Ag + [0 (dissolved)] [1] oxygen diffused from the interior of the silver electrode to the silver/electrolyte interface where the oxygen activity had been lowered from a fixed initial value to practically zero by the application of voltage to the cell. The diffusivity of oxygen in solid silver was determined from the solution of the diffusion equation and the time dependence of the cell current. However, this determination of the diffusion coefficient depended upon a knowledge of the solubility of oxygen in solid silver. A cylindrical geometry was used for the cell Pt, O2(Po2 = 0.21 atm) | ZrO2 + (CaO) | Ag + [0 (dissolved)] [II] which also allowed the diffusivity of oxygen in solid silver to be determined. These values were in agreement with other available data.l9 Recently, Raleigh20,21 used a method involving the measurement of diffusion-limited currents in a cell involving the AgBr solid electrolyte to determine the diffusion coefficient of silver in Ag-Au alloys at 400°C. Diffusivity values on the order of l0-14 sq cm per sec were measured in the alloy composition range 10 to 60 at. pct Ag in a single experiment. From numerous electrical conductivity and galvanic cell measurements,9'22"26 the solid solution Zr0.85 Ca0.15 O1.85 has been established as an electrolyte with predominant oxygen ion conduction over a wide range of intermediate and high oxygen activities. For interrelating the thermodynamics and the kinetics of the dissolution of oxygen in solid copper in this investigation, a galvanic cell was constructed with FeO-Fe3O4 as the reversible reference electrode, the Zr0.85Ca0.15 O1.85 electrolyte, and a pure copper specimen under-saturated in oxygen as the other electrode. THEORETICAL ANALYSIS Three variations of a high-temperature electrochemical technique were used in this study to provide two determinations each of the solubility and diffusivity

Jan 1, 1970

Like it or not, CPD is upon us. As from 1 January 2006, all registered engineering professionals, i.e. professional engineers, professional engineering technologists, professional certificated engineers and professional engineering technicians, were required to undertake CPD in order to keep their professional registration current. The rules regarding CPD have been gazetted under Government Gazette No. 28328, Board Notice 131 on 23 December 2005, and they also appear on the ECSA website?www.ecsa.co.za. For the convenience of our members they are reproduced in full in this issue of the SAIMM Journal.

Jan 1, 2006

By E. J. Ripling, M. W. Toaz

Tensile tests were conducted on pure magnesium and on four commercial alloys over a variety of temperatures and strain rates. The high positive slope of the ductility vs testing temperature curves that is found over a short range of testing temperatures for these materaturerials was shown to result from the fact that the microstructure was not stable at these testing temperatures. Pure magnesium did not display a transition temperature, although its sub-room temperature ductility was low. This poor ductility resulted from a grain boundary weakness. The aluminum-bearing commercial magnesium alloys had a higher ductility than the pure magnesium. ness.Thealuminum-bearingcommercialThese alloys did exhibit a transition temperature and grain boundaries that were stronger than the grain material. Both pure magnesium and the commercial alloys began initiating cracks at strains equal to one half of their fracture strain. MAGNESIUM base alloys' enormous potential as structural materials lies in their high strength to weight ratios. At present, the high strength magnesium base alloys such as AZ-80, which will be discussed later, have about as high a tensile strength to specific gravity ratio as the highest strength wrought aluminum alloy, 75s-T6, and, of course, a much higher strength to weight ratio than structural steel. Further, since the magnesium base alloys develop their high strength to weight ratios with moderate strengths and extremely light weights, the ratio of load carrying capacity to the weight of many structures is relatively higher for the magnesium base alloys than their strength to weight ratios would indicate. This results because judicious increases in section size, such as increasing the depth of bending members or adding reinforcing ribs, can frequently increase the weight of a structure linearly while the strength and stiffness increase as the second or third power of the added weight. Strength and rigidity must be designed into lightweight structures by those techniques which establish multiaxial stress states. Consequently, strong, lightweight structures frequently also possess a greater propensity toward brittle failures. In order to insure against these catastrophic failures, an extra premium must be placed on ductility and toughness in light alloys. Current knowledge of the ductility and toughness behaviors—notched behaviors—of magnesium base alloys is limited.* Most of the magnesium base alloys * The state of present knowledge regarding the effect of testing temperature on mechanical properties has recently been summar-ized by Pritchard.' crystallize in the hexagonal system, so that they are expected to exhibit a tough and ductile to brittle transition temperature. Actually, a transition temperature behavior has been reported for commercially pure magnesium in the literature, but the characteristics of this transition temperatureh uggest that it may not be a transition in the usual meaning, but simply the onset of some thermal softening, a performance much like that which face-centered-cubic lead might exhibit slightly below room temperature. If transition temperatures do exist, such important questions as the manner in which they are affected by internal variables such as chemical composition and grain size, or the effect of external variables such as rate of straining or notch severity have never been investigated. The investigation reported upon herein was undertaken in order to define some of the mechanical behaviors of the magnesium base alloys better, to gain a better understanding of the influence of some of the above listed variables, and particularly to understand their effect on ductility and toughness better. Material and Procedure Material-—Pure magnesium and four commercial alloys were used in this investigation. The alloys were selected so that chemically they made up a series with approximately the same minor alloying

Jan 1, 1957

By H. S. Martin

The Phosphate Recovery Corporation operates three flotation plants, Nos. 1 and 2 concentrators about three miles northeast of Mulberry, Florida, and No. 3 plant at Wales, Tennessee. These plants represent the first commercial phosphate flotation operation and are also believed to be the largest nonmetallic flotation operation in the world at the present time. The details of this paper will be confined to plant No. 2, this being the newest and largest concentrator in Florida, and the flow sheet being practically the same as at plant No. 1. The No. 3 plant has been operated but a short time and has been shut down since December, 1932, on account of the decrease in phosphate rock production. The phosphate washers usually are located centrally on a known deposit so that about two hundred acres of ground can be mined economically to each washer location. The washers are moved to new areas when the distance becomes too great for economical pumping. The flotation plants are built either adjacent to a washer, so that current debris may be utilized, or on the site of a former washer where there is sufficient accumulated debris available for mining, and the flotation plants must also be moved from time to time. Most of the water used in the Florida flotation plants is recovered after passing through a circulating system where most of the fine suspended matter is settled out, but some make-up water is obtained from deep wells near the plant. Power is obtained from the Tampa Electric Co. through the distribution facilities of the International Agricultural Corporation. Flotation concentrate is hauled from the plant by trolley over the International Agricultural Corporation's trolley system, to the drying plant at Prairie, one mile northwest of Mulberry. Ore Treated In the pebble phosphate district of Florida, the phosphate mineral, or collophane, is usually found in horizontal beds of varying thickness

Jan 1, 1935

By J. A. McCamley

Gypsum scrap generated from wallboard manufacturing, construction and deconstruction activities in North America, Europe and Japan is a recognized environmental problem. Landfill disposal of this gypsum scrap is problematic, with deposits often creating hydrogen sulphide emissions and metallic sulphide groundwater leachates. Of these regions, Europe is the most advanced in dealing with the issue having enacted legislation, which will come into effect in July 2005 that will strongly encourage gypsum recycling throughout the EU. An estimated 10% to 17% of all gypsum used in the wallboard industry becomes recyclable scrap, which represents approximately 1% of the total waste stream in North America. In the United States, 2.5 to 4.5 Mt of gypsum scrap is generated each year; the volume is similar in Europe (the percentage of total tonnage is less because of the higher use of brick and concrete). The Greater Vancouver region of British Columbia has banned gypsum from its landfills, and as a result, all gypsum scrap is now recycled. New West Gypsum Recycling, a Canadian firm, uses its proprietary technology to process large quantities of gypsum scrap that is reincorporated into new wallboard, at percentages ranging up to 25%. The operation of New West Gypsum Recycling Inc. of Langley, Vancouver is examined as a case study and recommendations are provided as to how other urban regions can implement similar gypsum scrap recycling programs.

Jan 1, 2004

By Marco D. Boscardin

Control and mitigation of building response to construction activities are assuming a greater role in design decisions for underground construction. Alternatives for controlling building response have multiplied with the continued development of ground modification methods, better control of construction activities that cause ground movements, and increased understanding of building behavior and response. This paper describes approaches to estimating building response to construction-related ground displacements caused by adjacent excavation and highlights the discussion with several case history examples. Examples discussed includes experiences with two, seven-story historic structures, supported by timber piles with granite block pile caps, which were underpinned in preparation for ground-freezing ground stabilization and tunnel construction beneath the buildings. The elevation of each building column was monitored and elevation adjustments were actively performed during construction. The second example examines the performance of a slurry wall braced cut, 45 to 50 feet deep penetrating through a stiff crust into a soft clay layer and associated building response. This cut was immediately adjacent to two, approximately 15-story office buildings, which were supported by deep foundations founded in the stiff crust.

Jan 1, 2003

By L McCracken

Up until 1990 CoalCorp North Island's accident record was six times that considered acceptable in those NSW operations with good accident prevention programmes. This was an obvious avoidable burden on the company in both human and cost terms.   Late in 1989 an accident prevention programme was implemented with the objective of achieving a 50 per cent reduction in the lost time accident frequency rate within 12 months. The key to achieving this objective was recognised as being an attitude change in the total workforce from General Manager downward. Management commitment and action were seen to be critical to the success of the programme.   Through very basic and simple training programmes in accident investigation, analysis and reporting, communication, on-the-job coaching and in focusing on improving supervision skills, the original objective was achieved.   During 1991 the application of methods improvement and hazard recognition techniques are seen as the logical step to achieving a further 50 per cent reduction in the accident frequency rate.

Jan 1, 1991

By Vincent Tirolo

Two separate secant pile cofferdams were constructed as part of an extensive rehabilitation and modernization of the New York City Transit's Lexington Avenue/Third Avenue IND Station at 53rd Street in Manhattan. Major high rise structures and outpatient hospital facilities bordered the site. The roadway is an important east-west corridor in mid-Manhattan. In order to perform the construction of new escalator and elevator shafts over 250 linear feet of secant wall was installed to the top of rock or to the existing subway roof. Much of the secant wall was constructed from below a temporary roadway decking system using a low headroom rig. The roadway decking system was supported on shallow spread footings. The secant piles were drilled using crawler mounted hydraulic rotary drill rigs. The secant wall provided a watertight, rigid cofferdam that minimized settlement and other disruptions to existing structures and utilities. During later stages of the project the secant wall also supported the roadway decking system.

Jan 1, 2003

By J. Coffin, R. Multani, C. Deredin

Glencore’s Strathcona Mill has recently evaluated a pyrrhotite depressant combination of diethylenetriamine (DETA) and sodium metabisulfite (SMBS) to improve its overall plant pyrrhotite- pentlandite (Po-Pn) selectivity, with the aim of producing a higher quality nickel concentrate. In a previous paper, key findings from a comprehensive lab-scale program (completed at the XPS Centre) were summarized where, of the depressants tested, DETA/SMBS combination was found to be the most effective in improving the Po-Pn selectivity. The present paper describes the metallurgical program recently completed at Strathcona Mill; DETA/SMBS evaluation on select plant “grab” samples as well as the major results of three DETA/SMBS plant trials conducted on several plant ore feeds (long-term testing). Interestingly, it was found that there was variable success in using DETA/SMBS depressants on the different plant ore feeds; DETA/SMBS (dosage: 25/50 g/t milled feed) on lower Cu feeds demonstrated a ~2% Ni recovery increase at the same Ni grade. On the other hand, higher Cu feeds demonstrated virtually no benefit from DETA/SMBS at the same plant dosage, suggesting that higher DETA/SMBS dosage (at specific locations) than that tested is required to overcome the increased Cu-DETA complexation for these particular feeds. Glencore Nickel – Sudbury Integrated Nickel Operations owns and operates Strathcona Mill which has been processing Ni-Cu ores from the Sudbury Basin since 1968. The valuable sulfides are pentlandite (Pn) – (Ni,Fe)9S8 and chalcopyrite (Cp) – CuFeS2, majority of the sulfide gangue is pyrrhotite (Po) – Fe(1-x)S [0 < x ≤ 0.125] which is present in two forms: hexagonal Po (Fe9S10) and monoclinic Po (Fe7S8) (Multani & Waters, 2017; Lawson et al., 2014). Currently Strathcona Mill processes ore mined from two primary sources from the Sudbury area and produces two concentrate streams: (1) nickel-copper concentrate that is sent to the Sudbury Smelter; and (2) copper concentrate that is shipped to the Fonderie Horne (Glencore Copper, Rouyn-Noranda).

Jan 1, 2019

By R. H. Estrada-Ruiz

This work analyses a new approach to estimates bubble size distribution of froth surfaces using artificial neural networks (ANN).Also, the robustness of ANN to interpret images with illumination perturbations, produced by light problems or dirt attached to the window of the video camera is evaluated. The experimental work was carried out in a laboratory flotation column, instrumented with an image acquisition system. The images were processed making use of a perceptron model with a hidden layer, sigmoidal transfer function and unitary bias, and the ANN trained with a back propagation algorithm. The results of validation show that ANN are reliable for learning and producing generalized predictions of the froth mean bubble diameter and bubble size distribution, when the model is trained using a database that contains information on the illumination intensity. Keywords: image analysis, neural networks, bubble diameter, bubble size distribution.

Jan 1, 2009

By Bernard H. Hertlein

Transportation system structures have come under very close scrutiny in the last couple of years, largely due to the damaging effects of disasters, both natural and man-made. In the Pacific northwest and California, earthquake risk is a major concern. In the central and eastern states barge impacts on bridge piers and docks are a big worry. In all cases of bridges over water and waterside structures, scour is a primary concern. Some of the results of this scrutiny have been changes in design and construction methods, and the introduction of more testing to supplement field inspection during construction, and throughout the service life of the structure. Future construction of bridges and docks will almost certainly see a continuing growth in these practices. Where foundations are concerned, particularly for bridges and waterside structures, many state and local authorities have started specifying drilled shafts rather than driven piles. Where the shafts must be constructed under water or slurry, visual inspection of most of the work is impossible, and one of several different Nondestructive Tests (NDT) is often specified. Contractors&apos; experiences with these methods have varied considerably, and there is a great deal of controversy in the deep foundation industry over the reliability of NDT methods for assessing the integrity of foundation shafts or piles. The author has had more than 15 years of practice with the various NDT methods for deep foundations, on projects all over the US, particularly foundations for bridges and dock structures, and has developed an understanding of the "NDT controversy" as it has become known. In particular, experiences in the Pacific Northwest, California, and Alabama have illustrated the reasons for the controversy. This paper reviews these experiences, and suggests some steps that owners and contractors can take to reduce the risk of inconclusive or downright inaccurate test results.

Jan 1, 1998

By S. Makni, A. Faucher, F. Robichaud, A. Bouajila

"Optimizing the ball charge in a grinding mill may be needed to maximise throughput or alternatively, to achieve proper product size in more challenging situations. Efforts to optimise the ball charge however are essentially empirical and suffer from the lack of appropriate, accessible and reliable tools. To address these limitations, a new model-based technology was developed that relies on 3D Discrete Element Method and population balance techniques: it takes on the form of a simulator that aims to significantly decrease the time required to optimise the size distribution and the grinding media load within a ball mill. This paper summarizes the research work related to the development of this simulator. The calibration of the different constituting sub-models will be highlighted. The successful use of the simulator to predict the effect of ball make-up on the grinding product size distribution in one plant is also reported.INTRODUCTION Adjusting the characteristics of the grinding media charge in grinding mills holds significant potential for optimisation of mill performance. For example, properly adjusting the ball size distribution in a ball mill can help achieving specified targets for final product size distribution and/or throughput capacity. However, several problems appear when reviewing the process and the available tools to optimise ball mill load: • The current empirical simulation tools are lacking with regard to the ability to predict the performance of grinding when changes to mill ball make-up are made; • Generally, these tools estimate the top size of the charge so it is difficult to predict the effect of mixed ball make-up; • As the quality of prediction of these tools is low, the operators try to optimise the ball charge by a ""trial and error"" method and proceeding with conservative changes. The influence of these changes on grinding performance is often less than the measurement precision and the improvements then remain imperceptible; • A change in ball make-up may require an average of about 6 months waiting period before reaching the stationary state of mill ball load. This exercise is due to be costly if applied change decreases the mill performance. In its effort towards the comminution process optimisation, COREM R&D portfolio had addressed the herein described opportunity during the last five years This paper describes the technology already developed for the optimisation of ball charge. It takes on the form of a simulator that aims to predict the evolution of the grinding media load, the grinding energy available in the ball mill and the final product size distribution. The simulator was first validated in a pilot scale ball mill and then applied in an industrial case."

Jan 1, 2012

By C. O. Brawner, J. Kalejta II

The classical approach to control rock fall and ravel in open pit mining has been to use catch benches. The width and volume of benches is most dependent on the bench height, size of loading equipment, blast damage to the face and mining regulations. This was compatible with open pit slopes of less than about 45°. As our understanding of rock mechanics and blasting control has improved over recent years, much steeper rock slopes can be developed at many open pit mines. However, narrower benches result with less rock fall capacity. The transportation industry has been very successful in using catch fences to protect highways throughout North America and Europe for years. The authors recommend that cable and ring net fences have a potential major application in open pit mining to allow steeper rock slopes with significant economic benefit. This paper outlines the application, design and operation of catch fences in surface mining for specific conditions. Typical case examples are presented.

Jan 1, 2002

By B. Elevli

The aim of this paper is to demonstrate the implementation of multicriteria analysis in selection of the most suitable underground ore transport system for a chromite mine in Turkey. The related problem includes five possible ore transport systems and six criteria to evaluate them. The adopted evaluation and ranking method for this study is PROMETHEE. PROMETHEE I revealed a partial order of alternatives where incomparability exists. PROMETHEE II gave the absolute ordering of alternatives. The results have shown that the PROMETHEE method can be successfully used in solving mining engineering problems. Keywords: multi-objective, decision analysis, mining, ore transport system

Jan 1, 2004

By Thomas Novak, Jeffrey L. Kohler, Joseph Sottile, Steve J. Gnapragasam

Modern underground coal mines can be very large, having a total connected load in excess of l5 000 hp. These mines generally have many miles of high-power conveyor belts and 15 or more miles of high-voltage power cables at distribution voltages of 12.47, 13.2, 13.8, or 14.4 kV. The shielded cables used in mine power distribution systems have a significant level of capacitance, on the order of 110 pF/ft. This level of capacitance, in an extensive power distribution system at today&apos;s voltage levels, can cause significant charging currents during a ground fault. This paper addresses the potential detrimental effects of capacitance charging currents during line-to-ground faults in mine power distribution systems. A representative mine power system is modeled, and simulations with faults at various locations are conducted to evaluate the effects of this capacitance on the level of fault current and relay selectivity. This paper also includes results of capacitance measurements made on mine power feeder cables used to validate the simulation model.

"The McArthur River uranium deposit is the single richest uranium ore body developed in the world to date. The ore body’s average grade is 15% U3O8. Proven reserves are in excess of 450 million pounds. The grinding circuit is located underground. The ground ore is pumped to a surface facility where the slurry is thickened and loaded into containers for shipping to the Key Lake mill 78 kilometers to the south.The paper will briefly describe the mining method employed. The underground ore handling and grinding circuit, and surface facilities including slurry load out, wastewater treatment and the freeze plant will be described in detail. The paper will emphasize radiation and safety procedures that are followed to minimize operator exposure to radiation risks.LOCATIONThe McArthur River mine is located 78 kilometres north of the Key Lake mill. It is located at latitude 57’ N in northern Saskatchewan, within the southern boundary of the Athabasca formation. The nearest town is Pinehouse, located 320 kilometres to the south. Access to the mine is by an all weather road and by a private airstrip.HISTORYThe McArthur River Operation is jointly owned by Cameco Corporation (69.805%) and Cogema Resources Inc. (30.195%). Exploration for uranium in the McArthur River area started in 1980 by the Saskatchewan Mining Development Corporation, a predecessor company of Cameco.In 1984, a 12-kilometre long basement conductor was identified at a depth exceeding 500 metres. Systematic exploration drilling of this conductor resulted in the discovery of the P2 North deposit. Subsequent surface drilling programs from 1989 to 1992 delineated a narrow ore zone over a strike length of 1700 meters at a depth of 500 to 600 metres. At this time, geological reserves for the deposit were estimated to be 2.4 million tonnes at a grade of 5.0% U3O8 for a uranium content of 260 million pounds U308"

Jan 1, 2001

By M. Görnerup, M. Hayashi, S. Seetharaman, C. -Å Däcker

The mould flux plays a crucial role in the continuous casting operation of steel due to its multi-functional assignment as lubricator and heat flux controller. In reality, the commercial fluxes can fall short of the expectations of the operator. In such cases, the performance of the mould flux reduces production throughput in the casting machine. This paper presents the results of a study of two different commercial mould fluxes in continuous casting of steels. The results of online sampling during casting, as well as off-line measurements in the laboratory, are presented. Mould flux powder and slag samples from the caster have been characterized with respect to melting behaviour, interfacial tension and thermal diffusivity, using various measuring techniques. An experimental technique has been developed in order to simulate the melting behaviour of a flux in the mould, which has been found to be useful for qualitative studies. A cross-sectional view of different powders reveals that up to four different material layers may exist in the bed: a loosely packed powder layer, sintered layer, semi-solid layer and liquid slag layer. It is found that the melting rate of the mould flux is dependent on the liquid slag layer thickness. Thus, in a continuous casting operation the melting rate is likely to be non-uniform with position in mould due to the difference in liquid slag layer thickness. Mould slag composition is found to be influenced by the starting powder for as long as 30 min, representing a large part of the first heat casting time. Observations of gas formation indicate that interfacial reactions between the steel and slag take place. Keywords: continuous sacting, mould flux, mould slag, properties

Jan 1, 2004

By Paolo Heiniger

The aim of this paper is to present the operative solutions devised and then adopted to implement the underexcavation (soil extraction) of the Tower of Pisa, by means of soil extraction. The intervention has been performed by the Consorzio Progetto Torre di Pisa, a joint venture made of five qualified Italian companies (Trevi S.p.A. , Rodio S.p.A., Italsonda S.p.A., Ismes -Enel Hydro S.p.A., Bonifica S.p.A.), selected for their experience in the field of monitoring and restoration of monuments, structural design, foundation engineering and specialised works in underground conditions. Since 1991 the Consorzio has been charged with the specific task of implementing, within the contractual frame of a Concession, all the decisions made by the International Multidisciplinary Commission appointed by the Italian Government the previous year, with the aim at solving the «problem» of the Tower, strengthening the structure and stabilising its foundation. The Trevi Group, which is represented by Trevi S.p.A. in the above mentioned Consorzio, has given and is giving its direct and constant contribution and is engaged in supplying the special equipment to the operation and the drilling technology which has been successfully adopted to date.

Jan 1, 2000