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By S. C. Gouws

"SynopsisSustainable infrastructure development has long been identified as a key enabler for socio-economic growth and poverty reduction in societies globally. Twenty-one years into the young South African democracy, economic prospects are fragile and unemployment statistics are high. According to Trading Economics (2015) the GDP growth rate in South Africa averaged 3.07% from 1993 until 2015.Through the National Development Plan 2030, the government has responded by instituting the Presidential Infrastructure Coordinating Commission (PICC) to direct national growth and drive job creation by effecting a long-term infrastructure investment programme. The Commission is mandated by Cabinet to coordinate, integrate, and accelerate implementation of more than 150 individual social and economic infrastructure plans.In the civil infrastructure development sector, increased urbanization is compelling governments and the public sector to expand safe and reliable public amenities, but the availability of real estate for construction in congested cities is a challenge. Within the mining infrastructure construction industry safe, rapid, and efficient mine extraction strategies are imperative to realize increased production, business hurdle rates, and stakeholder expectations.Asset owners and stakeholders are obliged to consider advanced mechanized underground excavation and support technologies in order to present feasible solutions timeously. From an engineering design, procurement, and construction management (EPCM) perspective tunnelling technology and boring applications have a distinct advantage over conventional excavation techniques. These solutions may enhance commerce and transportation by expanding infrastructure in concentrations of national economic activity, providing crucial linkages with rural areas, between cities, and across international borders.This paper explores the contribution by mechanized tunnelling technology and boring applications applied in conjunction with digital and automation technologies compared with conventional methodologies. The technological expertise, combined with a paradigm shift in delivery of project objectives, will promote economic growth, aid recovery from the economic downturn, and improve social development."

Jan 1, 2015

"Integrity tests refer to a variety of non-destructive tests (NDT) whose purpose is to measure or determine the quality and uniformity, and some- times dimensions, of cast-in-place concrete foundation elements. The tests are primarily aimed at detecting zones of poor quality concrete, voids, bulges, and/or necking.The non destructive integrity testing techniques in this section most generally used for drilled shaft testing are based on one of two physical principles - stress wave propagation or nuclear radiation. All of the stress wave methods involve monitoring a deliberately created vibration, usually of very low amplitude (strains on the order of ??). Some methods rely on direct transmission of the signal, while others rely on processing reflections of the imposed signal.The stress wave methods are inherently sensitive to vibrations from other sources, especially at frequencies that fall within the range of interest for the particular test being applied. Construction activity near the shaft being tested; such as: demolition jack-hammering, pile-driving, casing vibration, excavation and movement of track-vehicles are all known sources of interference that might render test data useless. The actual effect of such vibrations will vary with the type of activity, soil conditions and distance from the testing. The test operator must be able to recognize such interference, and the contractor should be prepared to cooperate with the testing personnel by stopping or moving the source of vibration. If this cannot be done immediately, testing should be postponed until the work in question is finished and the vibration source moved or shut down.NDT methods are not suitable substitutes for routine "topside" construction inspection as described in the Drilled Shaft Inspector’s Manual. However, these NDT methods do allow measurements of the quality of concrete placed in drilled shafts, which cannot be made from "topside" construction inspection. They should be considered supplemental to routine construction inspection as they do provide an additional level of quality control."

Jan 1, 2004

By Frederick J. Browne

Water, water everywhere, but not a drop (fit) to drink! Trite, but how often only too true? What is there met with in mining which, under various circumstances, may be said to be the most sought-for and highly-prized and also the most objectionable and most feared? Water! What visions that combination of five letters brings to all thoughtful minds? Up to near the end of the eighteenth century water was thought lo be an element but was then discovered to be the result of the combustion of two volumes of hydrogen with one volume of oxygen, and water so produced is chemically pure. Pure water is a clear and colourless liquid when seen under ordinary conditions, but appears bluish when seen through a long tube, and this same bluish tint may be observed in many lakes, especially those of glacial origin. A story often told describes a prospector in the desert who, failing to find water to replenish his canteen, suffers torture and death under fearful circumstances. Then again we may recall the flooding of mines, where water poured in so quickly that there was no opportunity of saving the unfortunate workmen. Instances might be multiplied without number showing that either the lack or excess of this essential fluid has taken heavy toll of human life. In all branches of mining and associated industries water must be dealt with to a larger extent, from an economic point of view, than any other substance, and very often the purity of the water is a matter of considerable importance.

Jan 1, 1925

By Sean Gallagher, John R. Bartels, Dean H. Ambrose

Remote operation of continuous miners has enhanced the health and safety of underground miners in many respects; however, numerous fatal and non-fatal continuous miner struck-by accidents have occurred when using remote controls. In an effort to prevent these injuries, NIOSH researchers at Pittsburgh Research Laboratory examined the workplace relationships between continuous miner operators and various tramming modes of the equipment using motion captured data, predicted operator response times, and field- of- view data to determine causes of operator-machine struck-by events in a virtual mine environment. Factors studied included machine speed, direction of escape, operator facing orientation relative to the machine, work posture, distance from machine, and operator anthropometry. Close proximity to the machine, high machine tramming speeds, a right-facing orientation and operator positioning near the tail all resulted in high risk of being struck. It is hoped that this data will provide an improved rationale for operator positioning for remotely operated continuous miners.

By X. Cui

Hydrocyclone is widely used in closed-circuit grinding process. However, in the first classification operation of coarse particles with high pulp density, the shortcomings of traditional cyclone are that the grinding cycle load is much high, the apex of cyclone is easily to be blocked and classification efficiency is less. Specifically, the problems of traditional cyclone used in grinding process are as follows: (1) Mill utilization factor is low and its handling capacity is small. (2) Coarse particles mixing in cyclone overflow affects the following separation process and fine particles mixing in underflow causes over-grinding, which affects the total recovery rate of valuable minerals. (3) High grinding cycle load leads to large amount of high-density slurry pumping, which causes high energy consumption and severe wear of cyclones, pipelines and pumps. The applications of new type pre-classification hydrocyclone with centrifugal volute in the first classification process of Iron Mine Mill are introduced in the paper. Pulp particles fed in the centrifugal volute were arranged in advance, so that coarse particles can be far away from the overflow pipe, which can reduce the short circuit current to avoid coarse particles entering overflow and improve classification efficiency and accuracy of cyclone. The strong points of the new cyclone in the coarse classification operation are as follows: (1) finer overflow and less fine particles mixing in underflow improves classification efficiency more than 10%; (2) lower ball mill load cycle improves ball capacity more than 10%;(3) grinding energy consumption reduces by more than 20% and cyclone feed pump reduces energy consumption by more than 12%. In short, new type pre-classification cyclone with centrifugal volute solves the problems of fine particles mixing in underflow, high grinding cycle load and less classification efficiency in the coarse classification operation. Therefore, it has broad application prospects in ferrous metal and non-ferrous metal ore dressing plant.

Sep 1, 2012

By Jian Li, P. Liu, R. Zhang and J. Lo

In the past decades, focused ion beam (FIB) has evolved into a powerful microscope that provides capabilities that no other microscopes can offer. The combination of high-resolution imaging and stress-free ion beam cross sectioning provides valuable microstructure information both at the specimen surface and beneath. FIB techniques are also the preferred method to prepare site-specific transmission electron microscope (TEM) specimens. CanmetMATERIALS owns a world-class microscopy facility, where advanced microscopy work provides strong supports to research programs that cover a wide range of subject areas. This paper is aimed to provide a few practical examples of FIB applications in microstructure characterizations that include cross-sectioning and imaging, serial sectioning, and advanced TEM specimen preparation in materials research at CanmetMATERIALS.

Jan 1, 2015

By A. G. Metcalfe, A. Siede

The hardening of annealed copper during fatigue testing appears to be independent of the applied stress and to occur largely within the first 4000 cycles. Copper hardened by fatigue is more resistant to annealing than copper hardened by static means, and softens by a multistage process. Creep studies at 300°C show that copper hardened by fatigue also has greater resistance to creep than statically hardened copper. Some theoretical explanations are discussed. RECENT interest in the behavior of metals subjected to fatigue stems from observations of phenomena which could not be explained by current theories of the structure of metals. In 1953 Bullen et al.l showed that the hardening caused by fatigue at low stresses did not cause severe bending of the lattice as did hardening by static methods. This was later confirmed by Wood, 'and Broom and Ham.3 Clarebrough et al4 showed that as the stress level used in fatigue hardening was increased, bending of the lattice was introduced, eventually approaching that of metals deformed by conventional cold-working methods. The type of hardening introduced by fatigue has other interesting characteristics. Kemsley5 showed that copper fractured by fatigue at low stresses resisted annealing as compared to copper hardened an equal amount by static means. The work of Clarebrough etal, shows that the manner of energy release during annealing differs for fatigue-hardened and statically hardened metal in both magnitude and temperature range of release. In addition to hardening of the lattice, fatigue has been shown to cause softening in materials previously hardened by static methods,5 and also in age-hardened alloys.7 The superposition of a small fatigue stress on the static loading of high-temperature alloys has been shown to increase their resistance to creep.' The present work was an attempt to determine the relationship between fatigue hardening, resistance to annealing, and the creep properties of pure copper. EXPERIMENTAL PROGRAM The program described here was designed to answer three questions: 1) Can stress-cycle combinations well below the failure values give significant increases in hardness? 2) Does hardening, under different stress-cycle combinations, give increase resistance to annealing? And if so— 3) Does superior resistance to annealing confer superior creep properties over statically hardened material? Three-quarter hard OFHC copper was annealed in vacuo at 550°C for 1 hr to produce a strain-free material having a fine grain size and uniform hardness. (The standard deviation of the mean hardness of the annealed samples was less than + 1.9 Dpn). Annealing was performed after machining the fatigue specimens so as to avoid work-hardened surfaces. Jigs were used to avoid distortion. The fatigue properties of the annealed copper were determined using an accurately aligned Baldwin-Sonntag SF1-U machine operating at 1800 cycles per min. This limited the minimum number of cycles which could be examined to about 4000 stress reversals. Since failure resulted in specimen damage, hardness increase with number of cycles was measured by testing specimens fatigued to different fractions of the failure values. The results are shown in Fig. 1, and are superimposed on the S-N curve of the copper in Fig. 2. The resistance to annealing of fatigue-hardened material was compared to that of material hardened by uniaxial tensile straining. Specimens hardened to equal values by both methods were progressively annealed for 1 hr at temperature in vacuo. After each annealing treatment the hardness was measured using a Leitz Durimet hardness tester with a 500-g load. At least five tests were made for each hardness determination. The standard deviation for individual specimens varied from 0.26 to 1.48 hardness points. The results are shown in Figs. 3 to 5. The discontinuous nature of the annealing process has been brought out by drawing idealized curves through the data points. This can be justified by the consistency of the results as well as by general agreement with results of Kemsley.5 The creep resistance of fatigue-hardened and

Jan 1, 1960

By I. L. Feld

This Bureau of Mines report describes the development of a simple method of producing low-phosphorus hematite concentrates from certain submarginal southeastern iron ores. The investigation was undertaken to obtain additional information on the Clinton iron ore outcrops at the southwestern extremity of the Birmingham district of Alabama and to assist in the development of operating techniques that would make it profitable to use the marginal ores of this area for blast-furnace feed. Batch and continuous pilot-plant tests demonstrated that a relatively simple wet scrubbing treatment) followed by a desliming operation to reject argillaceous (clayey) gangue, consistently yielded a marketable granular hematite product. Iron losses were relatively high but could be tolerated in view of the low treatment cost.

Jan 1, 1960

By Roger G. Rowe

The Crandon deposit, located in northern Wisconsin, is a 65.8 million ton Precambrian volcanogenic massive sulfide deposit which averages 1.4% copper and 5.8% zinc. The deposit is classic in origin, mineralogy and shape. Comprehensive understanding of the geology of both the deposit and the project site has been fundamental to the credibility and success of Project feasibility studies and regulatory permit preparation. Mine development in the current investment and regulatory climate requires thorough and timely application of geologic tools. From 1977-1980 geologic activities were focused on the typical objectives of orebody delineation, reserve estimation, depositional geology, and general site investigation. Results from these programs formed the basis for the Project's preliminary feasibility studies. Since 1981 further geologic investigations have provided criteria for project design, site management, and operational permitting. Activities have included mine entry position definition drilling, developing geostatistical reserve modeling, large diameter (150 mm) core drilling for mill pilot samples, rock mecha¬nics testing, and evaluation of the glacial overburden/deposit geohydrology for computer simulation.

Jan 1, 1983

By G. C. Howell, H. A. D. Kirsten

The mining-induced effects around narrow tabular stopes have traditionally been evaluated in terms of elastic continuum analyses. An understanding of the phenomenological behaviour of the rock surrounding deep-level gold mines has accordingly been developed on the basis of such analyses. However, elastic analyses do not afford reliable representations of the behaviour of rock in which failure may occur on discontinuities. This paper describes investigations that show how the stress and stiffness characteristics of a rockmass are affected under such circumstances for representative ranges of values for the relevant parameters (depth, span, support stiffness, field stress ratio, and discontinuity strength). These investigations afford a substantially different understanding of the mechanical behaviour of rock that is subject to failure. Instead of forming an arch across the abutments, the rock in the hangingwall bears directly across the stope onto the footwall and, instead of being subjected to tension, the nether hangingwall is clamped in compression in the horizontal direction.

Jan 1, 1993

By Ananta L. Yennamani

Blast movement measurement (BMM) transmitters are a practical method to measure three-dimensional (3D) rock movement because of blasting. The BMM transmitters are activated, programmed and installed in specially designed drill holes prior to the blast and the BMM detector locates the transmitters after the blast. The BMM software then calculates and summarizes the 3D movement of each BMM transmitter ball. This information helps to redefine the ore and waste boundaries and enables improved ore and waste selection, resulting in a genuine step change in grade control. The BMM program was carried out at Newmont Mining Corp.?s Phoenix Mine, in northern Nevada near the town of Battle Mountain. The mine is in a historic mining district that contains gold, silver and copper. The geology of the pit consists of different formations made up of sandstone, siltstone, limestone, chert-pebble conglomerate, shale, skarn and quartzite, to name a few. Some of the rock is extremely hard and a powder factor of up to 0.5 kg/t (1 lb/st) is required to get adequate fragmentation to ensure sufficient throughput through the crusher and the mill. The result of using such a high powder factor translates into considerable blast movement and heave. This movement means that the ore/waste digging polygons estimated by the ore control engineer from sampling the initial blast holes will no longer be located in their original posi-tions. The purpose of this project was to test the measurement method and to see if locating the digging polygons in the broken muck pile and excavating to those polygons will improve grade control through the mill. Case studies (Zhang, 1994), (Taylor, 1995), (Gilbride, 1995), (Harris, 1997), (Taylor, 2003), Barrick Goldstrike (Gold-strike Mine, 2008), Ruby Hill Mine (Hilkewich, 2009), (Porcupine Mine, 2005) and (Aguirre, 2010) have shown that, by accounting for the blast movement, there is a potential to increase mineral recovery by as much as 25 percent for individual blasts for only a modest cost increase.

Jan 1, 2011

By R. A. Kearns

To enable the mining industry to be kept informed as to the availability of equipment developed by mining equipment manufacturers in their constant endeavor to keep a step ahead of changes in mining techniques, the Bureau of Mines periodically issues lists of equipment approved subsequent to the last previous listing. The present list covers those approvals issued during calendar years 1953 and 1954. It supplements Bulletin 543, Permissible Mine Equipment Approved to January 1, 1953. The procedure established in Bulletin 543 of numbering items in each category consecutively to indicate the chronological order of the approvals has been continued in this circular. Information on approvals issued later than January 1, 1955 may be obtained by referring to Coal Age, a monthly magazine issued by the McGraw-Hill Publishing Co.

Jan 1, 1955

By Charles Sóstenes Assunção

A mathematical model of heat transfer and solidification for a continuous casting of round billets was developed. The water flux density of the secondary cooling zone was experimentally measured, using an apparatus in industrial scale with two types of nozzles, flat jet and full cone jet. The profiles of water distribution were applied on the mathematical model. The results showed that the water distribution is not uniform in both longitudinal and angular directions owing to the unevenness of the spray and to the curvature effect of the round billet. This non-uniformity causes important variation of the heat transfer coefficients and superficial temperature of the billet, especially in the first cooling zones, where the temperature is higher. The mathematical model was used to simulate a change of nozzle type in the first cooling zone. The results showed that the heat flux and superficial temperature variations were reduced with a full cone jet nozzle in comparison with the flat jet nozzles.

Aug 16, 2017

By John S. Stevenson

ZEBALLOS is a relatively new mining camp. It is on the west coast of Vancouver island, approximately 195 nautical miles northwestward from Victoria. Previous to 1934, a small amount of placer gold had been recovered from the Zeballos river and tributary creeks. However, it was not until the winter of 1934-35, when shipments of high-grade gold ore were made from the property of the White Star Gold Mines, Limited, that lode gold mining really began. Since then, several new mines and many promising prospects have been found. Milling in standard sized mills only commenced late in 1938, when the 75-ton mill of Privateer Mines, Limited, and the 50-ton mill of Spud Valley Gold Mines, limited, were first turned over. The most striking feature of the camp is the high-grade quality of the ore as usually mined. At one property, the ore along a drift 650 feet long has ranged from 5.8 ounces per ton to 17.5 ounces, over average vein-widths ranging from 8.3 inches to 14.5 inches in selected blocks along the drift. One . high-grade shipment of 196.6 pounds of ore from the same property contained 142.877 ounces of gold. The present paper deals only with that part of the area in which mining operations are most active, namely the main Zeballos River valley and its tributaries, Spud and Goldvalley creeks. During the summer of 1938, prospecting was carried on beyond this circumscribed area. The geology and early developments in the area have been described in the following reports: (1) CLOTHIER, G. A., Annual Report of the British Columbia Minister of Mines, 1929, p. 376; 1930, p. 441; 1932, p. 205; and 1933, pp. 252-254. (2) GuNNING, H. C., Geological Survey of Canada, Summary Report, 1932, Part A-II, pp. 29-50, Zebaltos River Area, Vancouver Island, B.C. (3) STEVENSON, John S., Annual Report of the British Columbia Min-ister of Mines, 1935, pp. F-38-40. ? ( 4) BANCROFT, M. F., Geological Survey of Canada, Memoir 204, 1937, Gold-Bearing Deposits on the West Coast of Vancouver Island Between Esperanza Inlet and Alberni Canal. (5) STEVENSON, John S., British Columbia Department of Mines, 1938, Lode-Gold Deposits of the Zeballos Area. (6) MAcDoNNELL, G. F., The Privateer Mine, Zeballos; The Miner, Van-couver, B.C., December, 1938.

Jan 1, 1939

By J. R. Boldt, C. M. Kleemann, V. N. Mackiw, B. Meddings, J. A. MacLellan, E. J. Maney, D. E. Halter, D. J. I. Evans, J. Honkasalo, M. F. Dufour

The technology employed in the processing of nickel- and cobalt¬bearing ores is a continually developing process for utilizing the natu¬ral resources available at a given time. Most of the nickel-bearing ores of commercial importance fall under the category of sulfide or lateritic ores. While the occurrences of both types of ore have been known for over a century, until 1960 sulfide ores largely from Cana¬dian mines have constituted the chief source of production for com¬mercial nickel in the Free World. Sulfide ores are readily amenable to some physical means of concentration, but the lateritic ores are not readily concentrated, and to compete economically with the sulfide ores only the high-grade garnierite ores (a type of lateritic ore) found in New Caledonia were processed to any great extent up to the time of World War II. Around 1960, a gradual shift in emphasis towards latetitic ores as a commercial source of nickel became evident. See Fig. 1. New discoveries of sulfide ores, usually located underground, had not kept pace with the steadily increasing demand for nickel. The lateritic ores, found near the surface of the earth, could be readily surveyed and mined. Lower cost processes were being developed for the extrac¬tion of nickel from lateritic ores and for a time it appeared that, based on pre-OPEC economics, the lower grade lateritic ores-down to 1.2% nickel-could satisfy an increasing share of the world demand for nickel. The sharp increase in the price of crude oil in the 1970s, however, slapped an economic damper on the lateritic ores. Processes for treat¬ing lateritic ores consume large amounts of energy; as the nickel industry entered its deep recessionary period in 1981-83, nickel pro¬duction from lateritic ores became less and less profitable than from sulfide ores. At the same time, new sulfide ores were discovered and brought into production, notably in Australia and South Africa. The chapters in Section 17 were prepared in 1973. Recent improvements in mineral dressing techniques since then include Inco's pyrrhotite separation process which can remove additional pyrrhotite from nickel concentrates, resulting in reduced sulfur dioxide emission from the Sudbury smelter, by some 25%. The chapters in this section dealing with nickel are grouped in line with the two broad categories of nickel ores. Starting with the description of nickel and cobalt ores in Chapter 2, Chapter 3 deals with the processing of sulfide ores, and Chapter 4 deals largely with lateritic ores. The intermediate steps to produce a suitable feed for extraction plants and refineries are similar in principle within the same categories, although dissimilar between sulfide and lateritic ores. Thus Inco in Canada employs flotation and so does Western Mining Corp. in Australia, although Inco's plants were started before World War II, and that of Western Mining only recently in the late 1960s. Treatment subsequent to the ore dressing step, however, shows some interesting differences. The earlier parts deal mostly with established and conventional practices, leaning heavily on pyrometallurgy in both

Jan 1, 1985

By Caroline B. Chapleau, Mélanie Proulx, Claude Bazin, Gaétan Lavoie

"Quebec Cartier Mining operates a pelletizing plant in Port-Cartier, QC. Grinding, agglomeration and pellets induration are the three main steps in the preparation of iron oxide pellets. In 1998, following different recommendations, the company increased the speed of one of its ball mill in order to increase the grinding efficiency of the machine. As expected, the increased speed lead to an increase of the power draught, which did not produce the expected increase of fineness of grind, neither its allows to increase the mill throughput. The change of behaviour of the mill could hardly be understood by comparison of discharge size distribution at initial and modified mill rotation speed. On the other hand, the use of the selection function from a population balance model provides an insight of the changes that occurred in the mill. This paper reviews the various steps required for the estimation of a grinding mill selection function. Results of the calibration to Quebec Cartier grinding mills show that the increase in the mill speed leads to higher rate of breakage of coarse particles, at the expenses of less efficient breakage of medium and fine size particles. In the case of the studied mill, breakage of coarse particles was probably not the critical step of the mill operation. INTRODUCTIONOre size reduction is the major energy consumption step in any mineral processing operations (Austin et al., 1984). Size reduction is required to either liberate valuable minerals from the gangue minerals in which they are imbedded, or to increase the specific surface of the ground material. Plant engineers continuously face the challenge to find grinding machines, operating conditions or grinding circuit flowsheet configurations that could improve the size reduction process at lower energy or m6dia consumption."

Jan 1, 2000

By Irving Hartman

The results of the first experimental study by the Bureau of Mines on the explosive properties of metal powders were published in 1945. Since that time the explosibility of numerous other industrial dusts and powders has been investigated. Part of this information has been published, but most of the data has not been released to date. This paper summarizes the results of experiments on 22 samples of titanium, zirconium, thorium, uranium, and hydrides of these metals. The major part of the investigation was made under cooperative agreement with the Atomic Energy Commission.

Jan 1, 1951

By Davey Bickford, Johan Hawinkel

Blasting and the use of civil explosives are a critical step in the mining process. Good decisions provide significant downstream benefits and create a safe and sustainable working environment, while poor decision making and judgement can have catastrophic consequences on workers safety, critical infrastructure or the security of the general public. An ever-tightening regulatory framework increasingly exposes manufacturers, transport companies and mining companies to the consequences of breaches resulting from erroneous or ill-informed decisions. In this context, new capabilities are required providing all actors in the explosive supply chain with tools to make better informed decisions allowing the individual to own up to his or her decision. Additionally, the traditional risk-control approach in the explosive supply chain up until usage and waste elimination, through administrative control procedures and processes, is becoming increasingly inadequate. In this era of digitalisation and automation, technology will play a pivotal role in ensuring safety and security in storage, transport and usage of civil explosives using the latest advances in electronics, communication technology and information technology. This paper explores the journey through time of technology in the civil explosives market to provide testing, measurement, analysis and control tools. This ultimately leads to better decision-making, ensures full accountability of the decision maker and uses the same technology to review decisions for process improvement, in the settlement of disputes or for the investigation of incidents. Additionally, the paper discusses the application and integration of electronic and digital technology in explosives and initiation systems as engineering controls for blasting associated risks. Finally, this paper reviews two practical cases of technology integration for risk management and improved decision making; the use of integrated GPS technology in initiation systems as an engineering control in the blast evacuation process and the use of RFID technology in explosive tracking from cradle to grave.

By Bruce Hebblewhite

An ACARP-funded industry research project in Australia recently investigated the problem of premature rock bolt failures in underground coal mines. The project carried out limited sampling from 9 different collieries in NSW and Queensland, followed by a more comprehensive, controlled sampling from one colliery. Over 50 broken bolts were collected and subjected to metallurgical analysis at UNSW to determine both the steel composition and to analyse the fracture surfaces. Prior to this study, there had been anecdotal evidence of similar bolt failures from a number of sites within the industry. The sampling and analysis conducted by this project - whilst being below a statistically representative sample of the entire industry bolt population - highlighted the fact that bolt failures were continuing to occur at a number of sites, in both older and recently installed bolts. The failures were almost entirely attributable to stress corrosion cracking (SCC). It appears that a combination of factors - including steel composition, bolt manufacturing process, loading environment, geological and hydrological environment, bacterial corrosion - can all contribute to this problem. There is no simple solution, however, as with similar research findings from the UK, it appears that steels with higher values of fracture toughness, or Charpy Index, are less susceptible to SCC. Testing to date has been limited to bolt failures below the resin encapsulation horizon. A real concern is the potential extent of the problem at higher horizons, within the encapsulation. These may require some form of non-destructive testing (NDT) for detection. Initial trials in Australia of the ultrasonic device developed by DMT in Germany have proved encouraging. Further testing using this device is anticipated in future research. This paper describes the outcomes of the project, completed in 2002.

Jan 1, 2003

By F. N. Rhines, A. S. Nemy

The mode of high-temperature tertiary creep of 523-0 aluminum alloy was found to be strongly stress dependent. The occurrence of necking and/or fissures during tertiary creep exhibited a sequence with varying stress, wherein fissures with no necking occur at a minimum stress and necking with no fissures occur at a maximum stress. At an intermediate stress, tertiary creep begins without necking but with fissures in a region just beneath the external surface, followed by necking and the development of fissures along the axis of the specimen. The results are interpreted in terms of grain boundary gliding and the hydrostatic stresses produced by restraints to grain boundary gliding. THERE appear to be two possible reasons for the existence of a period of accelerating elongation prior to rupture during high-temperature creep in metals; namely, 1) a change in the structure of the metal itself, leading to a change in its response to loading, and 2) a reduction in the cross section of the metal resulting in a higher unit loading. Howe,' by annealing and retesting broken low-temperature creep specimens, found that irreparable damage is done once a metal is subjected to creep. Andrade2 first pointed out the association between the reduction in cross section and the increase in creep rate. The present research was designed to investigate both of these factors by retesting specimens machined from material which had been subjected to high-temperature creep testing short of rupture. EXPERIMENTAL METHOD An aluminum alloy, 52s-0, was selected for these studies because it is constitutionally simple, is strong enough to be relatively insensitive to mechanical damage during machining,3 and undergoes accelerating creep in a convenient temperature range. This alloy is hardened by 2.6 wt pct Mg in solid solution and is not subject to overaging effects; it has a very small quantity of an insoluble impurity phase, Mg2Si, finely dispersed throughout its micro-structure. Creep specimens, similar in design to ASTM 0.252-in. tensile specimens, were machined from 3/4-in. round stock and the surfaces were electro-polished. A 24-hr anneal at 500°C was then applied to stabilize the grain size to an average diameier of 0.27 mm. Subsequent heating for as long as 700 hr at the intended test temperatures produced no change in the tensile properties, indicating a well-stabilized state of the material. Corresponding to each of the typical testing conditions listed in Table I, one creep specimen was tested to destruction and this test was employed as a guide in the selection of times for subsequent tests. Duplicate creep tests were then run to various points along the creep curve to produce specimens which were used to determine changes in mechanical properties and microstructures. The latter were examined at the midsections of the specimens. Other specimens were tested to various stages of tertiary creep, after which they were remachined to new cylindrical test specimens, electropolished and re-tested in creep. RESULTS The major findings of this investigation may be illustrated by a comparison of the results of three sets of creep tests. These were run at 400°C at three stress levels, namely 750, 1000, and 1500 psi. In presenting these results in Figs. 1, 5, and 8, the creep curves are given in pairs: That curve of each pair which is drawn through filled circles corresponds to the initial test, and the curve drawn through open circles (and designated by - R) represents the result of retesting the same specimen after machining to a new cylindrical surface. The load was readjusted to the original unit stress at the beginning of each retest.

Jan 1, 1960