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Failure of rock materials is a process of crack propagation. Crack initiation takes place when the crack tip stress intensity K reaches a critical value called fracture toughness, K1C. The rock fracture toughness is known to be affected by the surrounding environment such as temperature, confining pressure and humidity. In order to examine the effect of humidity, a series of semi-circular bend tests were performed under various water vapour pressures in a rock material that is known to be anisotropic. Water vapour promotes stress corrosion of rock and therefore the fracture toughness was found to have a decreasing trend with increasing water vapour pressure. The rate of decreasing the fracture toughness depends on the microcrack density that promotes the migration of water vapour into the rock. Also in an anisotropic rock, the fracture toughness depends on the direction of crack in relation to the anisotropy of the rock material.

Dec 6, 2010

By Laurel E. Blackman

The DFI Project Information Management Systems (PIMS) Committee cooperated with the US Army Corps of Engineers (USACE) to develop a specification for PIMS used on USACE projects. Once completed the Committee developed a more generic version of this specification for general use, which is contained in this document. This first edition has simply removed the USACE-related requirements from the document. The committee will continue to work on this specification to enhance the content and also incorporate recent technological development for these systems. It is the Committee's intention that a second edition will be issued in 2022.

Jan 1, 2021

By Louis W. Cope

Many Americans have seen Greenland while flying over it on their way to or from Europe. Few have visited this largest island in the world. Portions of the 20 percent of the territory that are not ice-covered are highly mineralized. Greenland could become very productive if the present interest in exploration increases. The people and Greenland’s history The population of Greenland is 57,000. Twenty percent are Europeans, mainly of Danish decent, while 80percent are native Greenlandic or mixed Greenlandic-European. The native population is the same as the Inuit of the Canadian Arctic. They speak the same language.

Jan 1, 2004

By J. K. Gustafson

Since prehistoric times, gold has been sought for its beauty and its unusual physical and chemical properties. Early in the dawn of civilization it became the ultimate unit of value, and for at least 6000 years it has been used to barter for other commodities. It has been prospected for, treasured and made into works of art and personal adornment. From time to time, it has even been the object of conquest. Because of its predominant role as a basis for money in recent centuries, economists have come to think of gold solely in these terms. Gold, however, has physical and chemical properties that make it one of the most useful metals in the modern world. It is the most ductile metal known. An ounce of it can be drawn into a continuous wire over 35 miles long. It is also so malleable that an ounce of it can be beaten into films 0.00001 in. thick covering 68 sq ft of surface. It has a density of 19.3 and is so heavy that 1 cu ft of it weighs more than half a ton. Gold is nonmagnetic and has a high electric conductivity that is only slightly less than that of silver and copper. Gold is so inert to all the chemicals found in nature that gold coins and jewelry buried beneath the soil or at the bottom of the sea for thousands of years appear to be as bright and perfect as when they were first immersed. Finally, gold has an extremely high reflectivity of both light and infrared rays.

Jan 1, 1971

By Amy McBrayer, Andrea Brickey

Area mining is a surface mining method that allows for efficient mining and contemporaneous reclamation of tabular or bedded deposits, e.g., coal. Mine planning methods for area mines differ from those of open pit metal mines. Area mines in the Powder River Basin (PRB) use various processes for mine planning at both the strategic and tactical stages. With the ever changing commodity markets, it is becoming increasingly important for mine operators to be able to react quickly to the changing business environment. Tools that allow for the development and rapid comparison of production schedule scenarios are key to ensuring agile mine operations. A survey of mine engineers responsible for mine design and production scheduling at coal operations provides clarity on the current mine design and production scheduling processes in the PRB, as well as a discussion on potential solutions to upcoming challenges. In this article, we describe various mine planning processes used by the coal producers in the Powder River Basin. The survey identifies a clear gap in the ability to create comprehensive schedules associated with limited tools and lack of engineering labor needed to frequently conduct the mine design and scheduling process.

Jul 8, 2023

By G. B. Harris

It has long been appreciated that chloride chemistry has a number of advantages over the more traditional sulphate route for both extracting and separating metals. Modern materials of construction, coupled with the development of a more cost-effective and efficient hydrochloric acid regeneration technology mean that chloride-based processes are now more competitive and attractive. Such processing routes are able to recover more of the contained metal values in a feed, including iron in a benign and/or marketable form, and particularly the so-called rare and rare-earth elements which are increasing in demand in our electronic age. These factors, therefore, add appreciably both to the overall economics of a project, but also offer a much more sustainable approach to our dwindling natural resources. Additionally, chloride-based flowsheets can be much more environmentally-friendly, offering practical alternatives to two of the biggest headaches faced by the industry, namely cyanide usage and the generation of red muds. This paper presents a brief theoretical background, focusing on the latest developments of ferrous iron oxidation and the low-temperature, selective hydrochloric acid regeneration process, which is the key unit operation for any chloride flowsheet, and discusses in general the advantages of the chloride approach. Several recently-developed flowsheets, which have been tested at the miniplant level, are presented for gold, base metals, titaniferous magnetites and lead-silver ores wherein the advantages of considering a chloride approach are highlighted.

Jan 1, 2014

By Walter Fuchs

IT is now generally conceded that coal is the product of deposition and transformation of debris of forests and swamps.29 Ample data are available to illustrate the metamorphosis of biochemical substances through biological action; other data show the progressive regional metamorphism existing in coal beds;25 and numerous examples of change effected by intrusion of igneous dikes into coal deposits have been established .R3 However, often the relative importance of the biological and the geological factor in determining the character of the various natural coals is a debatable question. Since both biological and geological factors are ever present in nature, the problem, at first glance, would appear to resemble certain probability problems: specifically the simultaneous toss of two coins, with the biological factor as heads and the geological as tails. The probability is 2:I for the combined effect of both factors, as compared to the exclusive effect of either one, if the a priori probability is the same for each factor. This condition can be analyzed by a thermodynamic treatment of data, which may be obtained from a consideration of pertinent biological, chemical, geophysical and geological facts. SYNOPSIS OF BIOLOGICAL AND CHEMICAL FACTS The biosphere is not sterile; i.e., microorganisms are always present. Microorganisms have been established in the ocean deep, under the ice of the polar regions, in the sand of the deserts, and in swamps far below the surface. The various biological media may be acid, neutral, or alkaline, and they may or may not be readily accessible to air. Microorganisms are encountered almost everywhere, except where the temperature is not within the range tolerable by microbial life. Of course, with changing conditions, the type of microorganisms will change. All chemical products of life-proteins, fats, carbohydrates, lignins, waxes, resinsmay serve as a habitat of microorganisms. In the decomposition of a medium, some microorganisms macerate organic matter mechanically and remove certain constituents for their own nutrition; others decompose a large part of the organic matter but may leave certain constituents undecomposed. Some attack only certain specific ingredients of the organic matter. All of them build up cell substance. The nitrogen content of the medium largely determines the degree of decomposition. Below 1.7 per cent nitrogen, growth of microorganisms and hence decomposition of organic material is retarded; consequently organic material will accumulate.17,32 Such accumulations of organic material may give coal eventually. Coals differ in type and rank. The nature of the original vegetation and the conditions attending the transformation of the accumulated debris determine the type of coal such as bright, splint, cannel, and algal or boghead coals. Chemical analysis of representative samples of a given type of

Jan 1, 1941

THE solid nonmetallic inclusions present to some extent in all commercial steels have been variously designated. In early references they were usually called slag inclusions, and this terminology is still retained to some extent. On the premise that all nonmetallic matter produced in a metallurgical process is slag, this can be justified. We have come to think of slag, however, in a more restricted sense, and calling these particles slag inclusions is further objectionable because it fosters the erroneous concept that they are actually incorporated portions of furnace slag. Rarely is this true. The term sonims (coined from solid nonmetallic impurities) was proposed many years ago but never came into common use. In general, the term non-metallic inclusions seems to be satisfactory and adequate. NATURE AND CONS1lTUTION OF NONMETALLIC INCLUSIONS From the standpoint of origin, inclusions fall naturally into two classes: (1) those occurring as a result of reactions taking place in the body of molten or solidifying metal and (2) those resulting from mechanical incorporation of refractories or other materials with which molten steel comes in contact. The former are by far the more numerous and have been called indigenous, natural, or native inclusions. The latter are by their very nature sporadic in occurrence and have been called exogenous, accidental, adventitious, or foreign inclusions. They are often referred to as the "slag-stringer" type, though here also the material is not likely to be furnace slag. Substances Found in Inclusions. Nonmetallic inclusions are composed principally of oxides and sulfides but carbides and nitrides sometimes play an important role. In the case of indigenous inclusions the reactions by which these particles are precipitated from molten or solidifying steel may be caused by: (1) oxidation such as may occur during refining or during tapping and teeming, (2) deoxidation by added alloys, (3) change

Jan 1, 1964

By W. T. Malone, J. R. Williams, R. L. Tiner, J. M. Tinsley

Hydraulic fracturing methods for production stimulation have become a common procedure in the oil and gas industry. Fracturing treatments are performed on wells of various potentials to help increase the production rate. In addition to the desire for increased production is the need to predict what increase might be expected. This knowledge is useful in economical treatment planning to accomplish the desired production goals for the well. Theoretical production increases due to horizontal radial fractures may be calculated using equations developed from mathematical analyses and electrical models.1,2,6 It also is possible to predict theoretical production increases due to vertical fractures using curves developed from electrical3 and mathematical models.8 However, these studies assumed that the vertical fracture height and the formation height were equal, which may not be true." In addition, the final fracture height through which fluid is produced may not be equal to the created height. The development of vertical fracture proppant transport relationships has made unrealistic the assumption that propped fracture height is equal to created fracture height. Through the use of published proppant transport equations,4'12 it is possible to calculate the height of a bed of propping agent deposited in a fracture of a given height. Assuming that the fluid flowing in the fracture moves through only the propped portion of that fracture (i.e., that the un-propped part of the fracture heals) it becomes essential to know how production increase varies with the ratio of propped fracture height to formation height. It should be recognized that future investigation may determine that the fracture does not heal completely and that a highly permeable channel exists over the deposited bed of proppant. The effect of this channel was not considered for the present study. The following analysis of experimental data allowed development of curves to determine theoretical production increases considering fracture height as a variable. Discussion In designing a fracturing stimulation treatment a number of variables must be considered. The size of the treatment, type of proppant used, proppant concentration, treatment fluid properties and well conditions are all factors affecting the dimensions and permeability of the fracture. Production increase due to a vertical fracture is affected by propped length, height, width and permeability of the fracture for a given set of formation conditions. Production increase may be defined as the ratio of production rate after fracturing to the production rate before fracturing at the same pressure differential, pe — pw. The producing rate in an

Jan 1, 1970

By Marlion T. McQuinn

This paper will discuss the design, construction, and performance of the support of excavation on the Dulles East and West Automated People Mover Tunnels and Station projects. The elements of the system included drilled soil nails and rock anchors with reinforced shotcrete to the excavated face. We will discuss the geotechnical characteristics, design and construction considerations, loading criteria, construction techniques, schedule constraints, and performance of the support of excavation system. In consideration of the conference theme, there will be a discussion of the application of the real-time instrumentation monitoring program. The project team worked to design and install approximately 710,000 square feet of shotcrete and 19,000 soil nails/rock anchors as well as excavate over 720,000 cubic yards of rock materials within 15 months and in such a manner as to minimize the disruption to airport passengers and operations.

Jan 1, 2006

By C. R. Austin

Tan investigation described in this paper deals with the development of high-temperature alloys of the Konel series over a considerable period of time at the Research Laboratories of the Westinghouse Electric and Manufacturing Co. The word "Konel" has been coined to designate a class of alloys which are essentially nickel-cobalt-iron with other elements added, usually in small quantities. Most of these alloys contain titanium, usually about 2.5 per cent. The main consideration related to strength at high temperatures but the thermionic characteristics of the alloys was also of considerable importance. It is, however, with the mechanical properties at elevated temperatures that we are herein concerned. Much attention has also been devoted to their age-hardening characteristics. There is little need to stress the utilitarian aspect of this subject, as it has been discussed frequently. Alloys exhibiting superior properties at normal or elevated temperatures rapidly find many suitable applications. There may be some question, however, as to what constitutes a "superior alloy, " or an alloy that may have good service possibilities at high temperatures. The problem is complex and various means have been employed to predict the useful life that may be expected of a material. In recent years the "creep limit" has been used as the best means of evaluation. Such tests necessarily are prolonged and hence collection of data is very slow. In a general survey of many alloys therefore the creep test is not desirable and recourse must be had to much shorter time tests in order more rapidly to select alloys which appear to show promise. For this reason the present survey has been made using the high-temperature tensile test and a bend test developed by Howard Scott.1 In the tensile test the conditions have been standardized for all tests, so that values obtained are at least comparable, one alloy with another, although the absolute values recorded merely indicate the mechanical properties at the given temperature under a definite rate of loading.

Jan 1, 1931

The Annual General Meeting of the South African Institute of Mining and Metallurgy was held in Kelvin House, Johannesburg, on Wednesday, 27th August, 1975. Professor R. P. Plewman (President) was in the Chair. There were present 45 Fellows, 37 Members, 8 Graduates, 3 Associates, 4 Students, and 45 Visitors, making a total of 142. The President declared the Meeting open at 16h00. OBITUARIES The President: Ladies and gentlemen, it is my sad duty to announce the death of the following members of the Institute : M. Barcza, an Honorary Life Fellow and Past President of the Institute; J. A. Boyd, F. E. Keep, and J. H. Taylor, Life Fellows ; I. D. B. Corner, C. O'G. Deane, R. E. Gilmour, A. C. Hofmeyr, M. W. Howell, T. J. Robin, and F. S. Steinhobel, Fellows; J. J. Frankel, Member; and T. J. Higgs, Associate. As a mark of respect to the memory of the deceased and in sympathy with the bereaved, I ask you to rise and observe a few moments' silence. MINUTES The President: May we confirm the minutes of the General Meeting held on March 12th 1975 and published in the June issue of the Journal? Agreed. WELCOME The President: It is now my very great pleasure to welcome the many members of our Institute and all the distinguished guests who have honoured us with their presence this afternoon. In particular, I would like to welcome our Honorary President, Mr R. S. Lawrence, President of the Chamber of Mines, and also our Honorary Vice-President, Mr T. L. Gibbs, the Government Mining Engineer. Ons is ook besonder vereer dat dr. Naude, die Wetenskaplike Raad-gewer aan die Eerste Minister, en mnr. C. A. J. Borman, Direkteur van die Witwatersrandse Kollege vir Gevorderde Tegniese Onderwys, hier aanwesig is om die vergadering by to woon. We are also honoured by the presence of some 19 Presidents, Vice-Presidents, and Chairmen of our sister scientific and technical organizations. I would particularly like to welcome Mr Gericke of the South African Council for Professional Engineers, Professor Pretorius of the A.S. & T.S., and Dr Lloyd of F.S.P.E. And then, also the Presidents of the Institute of Welding, Professor Robinson; of the Electrical Engineers, Dr Troost ; of the Certificated Mechanical and Electrical Engineers, Mr Gibbs; of the Geological Society, Professor Maske; of the Land Surveyors of the Transvaal, Mr Course ; of the Assayers and Analysts, Mr Williams; of the Mine Ventilation Society, Mr Martinson; of the Chemical Institute, Mr Goodman; of the Association of Mine Managers, Mr Pretorius ; of the Institute of Foundrymen, Mr Attenborough; of the Production Engineers, Mr Duggan ; and of S.A.F.U.E.S., Mr Avalle. Then, the Chairman of the Council of the Institute of Metallurgists, Mr Snow; the Vice-President of the Town and Regional Planning, Mr Reinecke; the Vice-President of the Association of Consulting Engineers, Mr O'Kell; and Mr Cronje, who is representing E.A.S.A. Finally, the Chairman of the Southern Transvaal Section of the Chemical Institute, Mr Bloom ; the Chairman of the Witbank-Middelburg Branch of our own Institute, Mr Hosking; and the Secretary-Treasurer of our O.F.S. Branch, Mr Bird. We also have with us Mr Trueman; the Deputy Manager of Kelvin House, Mr Mrost ; our Honorary Editor, Dr Glen; Mr Walford; and also some representatives of the Press. Finally, it gives me great pleasure to welcome those who will receive Honorary Life Fellowships tonight, and also the winners of our student prizes. MEMBERSHIP The President: Ladies and gentlemen, I have pleasure in announcing the names of the following candidates, which have been published in accordance with By-Law 5.2.5., and Council has elected them to membership in the following grades: Fellows: R. G. Boswell, R. W. Chadwick, D. R. Hardman, J. A. Holmes, T. J. B. Jones, and R. P. King. Members : M. A. Bridgeford, C. F. Bonney, H. E. Bartlett, L. G. Floyd, A. K. Haines, D. Hatfield, C. G. Heymann, M. J. Howes, J. B. See, E. van Greunen, and S. P. Swanepoel. Associate Members : J. Coetsee and R. P. G. Steyn. Graduates: J. J. de Villiers and J. C. King. Associates: B. J. Bucher, P. A. Combrinck, W. J. N. Gelderblom, L. S. Halasz, J. van Wyk, C. P. Visser, and A. Veress. Students: D. J. Claasens, P. C. Crous, D. H. Murchison, P. A. Rossouw, and J. P. L. Schultz. Company Affiliates: Airco Engineering (Proprietary) Limited and Deelkraal Gold Mining Company Limited. There have also been some transfers: Member to Fellow: J. B. Nangle. Graduate to Member: E. E. Eichenbergen, M. J. Hillbeck, L. A. Melis, P. J. Venter, and R. O. Wellman. Associate to Associate Member: B. M. Williams. I welcome the newly elected members to the Institute, and I congratulate those who have been transferred to a higher grade.

Jan 10, 1975

By William P. Blake

The ancient city of Guanajuato, the capital of the State of that name, has been built up and sustained chiefly by the milling industry based upon the veins of the Veta Madre and La Luz. It is distant about twelve hours, by rail, from the City of Mexico. Its elevation above the sea is about 6300 ft., and it has a salubrious climate. The population, at the date of my visit in 1891, was estimated at from 80,000 to 100,000 persons. The place is justly celebrated for the antiquity, depth and extent of the mines, the magnitude of the deep shafts, and the enormous total yield of the district in silver and gold, which is comparable with that of the Comstock Lode in the United States. Several important public institutions are located at this center. The State office for the records of claims and of the statistics of mining and production is known as the Deputacion de Mineria. The Mining College, with its fine collection of ores and minerals from the mines of the region, is highly interesting to mineralogists. A mint for the coinage of silver, but not of gold, coins from four to twelve millions of' silver dollars annually. The silver received at the mint is melted in an open-hearth furnace, and is ladled out and cast into long and thin bars, which are rolled down to the proper thickness for the blanks. The bars contain some gold which is not parted. There is an export of dore bars to Germany, amounting in value to from $1,000,000 to $1,500,000 annually. There were, in 1891, upwards of forty reduction-works in and about the city where the silver ores were treated, chiefly by the ancient patio method. In these works were 65 Chilean mills, 301 arrastres of large size, and 936 of smaller dimensions. There were 36 steam engines, but mule-power was generally used at the ar-

Jan 1, 1902

By H. Kinilakodi

The authors previously developed a methodology that combines injury and citation measures into an overall mine safety performance evaluation tool, called the safe performance index (SPI). It can be easily adopted by mine operators to monitor trends in their injury and citation experiences as a risk assessment method. In this paper, six normalized safety measures and the SPI are used to evaluate the health and safety risk that existed at mines in the two years preceding the occurrence of a fatality. The percentage of mines is given for which the risk was high or where trends of some of the safety measures indicated moderate risk. In 50% of the mines, this mine safety performance tracking method could have been helpful to the companies, state agency or the U.S. Mine Safety and Health Administration (MSHA) in recognizing and addressing emerging problems with actions that may have been able to predict high-risk conditions, the fatality and/or other serious injuries. The approach would have given extra scrutiny to the risk for mines that encompassed 74% of the fatalities during 2007-2010.

Jan 1, 2012

By T. Hofbauer, M. J. Dry, G. B. Harris, C. W. White

"Urban Mining is a term that is increasingly being used, and represents an appreciable source of secondary materials for the metals extraction industry, a source that does not incur mining costs, but does, at present, incur considerable disposal costs. Electric Arc Furnace Dust (EAFD) is probably the most common of these materials, with an estimated global production of 8 million tonnes annually, of which 1 million tonnes is generated in North America. The contained annual metal value in EAFD at current prices is of the order of $6 billion, yet, apart from the zinc, virtually none of this is recovered.Despite many attempts over the years, with pyrometallurgical, hydrometallurgical or hybrid processes, currently the only commercially viable method of treating these materials is smelting in a Waelz Kiln (or a Rotary Hearth Furnace), which essentially recovers only the zinc, in an impure oxide form, and generates a secondary slag waste, which is still toxic and requires disposal. This paper describes the development of a chloride-based treatment process to recover all components of the EAFD in a marketable form, which centres around the novel hydrochloric acid recovery and recycle operation. Laboratory, miniplant and pilot plant data are presented, leading to the definition of a viable process flowsheet enabling the recovery of pure iron and zinc products (the principal components of EAFD), together with secondary products such as copper, silver, lead, cadmium, magnesium and manganese. A rigorous mass-energy balance is used to examine the preliminary economics involved."

Jan 1, 2014

By G J. Harbort, Z Pokra

It has been observed in several Jameson cell installations where the source for flotation feed is deslime screens, that the recovery of coal particles greater than 0.5 m is not as great as that of finer material. Consequently, a research project was undertaken at a CHPP in the Bowen Basin, Queensland, to assess the possibility of increasing the recovery of coarser particles (+0.5 mm) within the downcomer of the Jameson Cell. The effect of decreasing turbulence and agitation in a commercial-scale downcomer was investigated to assess the effect on the recovery of both coarse and fine coal particles. This paper details the findings of the testwork, summarising the results relating to differences in the operating parameters within the downcomer.

Jan 1, 2005

By C. R. Austin

THE investigation described in this paper deals with the development of high-temperature alloys of the Konel series over a considerable period of time at the Research Laboratories of the Westinghouse Electric and Manufacturing Co. The word "Konel" has been coined to designate a class of alloys which are essentially nickel-cobalt-iron with other elements added, usually in small quantities. Most of these alloys contain titanium, usually about 2.5 percent. The main consideration related to strength at high temperatures but the thermionic characteristics of the alloys was also of considerable importance. It is, however, with the mechanical properties at elevated temperatures that we are herein concerned. Much attention has also been devoted to their age-hardening characteristics. There is little need to stress the utilitarian aspect of this subject, as it has been discussed frequently. Alloys exhibiting superior properties at normal or elevated temperatures rapidly find many suitable applications. There may be some question, however, as to what constitutes a "superior alloy, " or an alloy that may have good service possibilities at high temperatures. The problem is complex and various means have been employed to predict the useful life that may be expected of a material. In recent years the "creep limit" has been used as the best means of evaluation. Such tests necessarily are prolonged and hence collection of data is very slow. In a general survey of many alloys therefore the creep test is not desirable and recourse must be had to much shorter time tests in order more rapidly to select alloys which appear to show promise. For this reason the present survey has been made using the high-temperature tensile test and a bend' test developed by Howard Scott.1 In the tensile test the conditions have been standardized for all tests, so that values obtained are at least comparable, one alloy with another, although the absolute values recorded merely indicate the mechanical properties at the given temperature under a definite rate of loading.

Jan 1, 1931

By M. R. Shahan, W. R. Reed, S. Klima, T. W. Beck, Y. Zheng

Testing was conducted to determine the ability of foam to maintain roof coverage in a simulated longwall mining environment. Approximately 27 percent of respirable coal mine dust can be attributed to longwall shield movement, and developing controls for this dust source has been difficult. The application of foam is a possible dust control method for this source. Laboratory testing of two foam agents was conducted to determine the ability of the foam to adhere to a simulated longwall face roof surface. Two different foam generation methods were used: compressed air and blower air. Using a new imaging technology, image processing and analysis utilizing ImageJ software produced quantifiable results of foam roof coverage. For compressed air foam in 3.3 m/s (650 fpm) ventilation, 98 percent of agent A was intact while 95 percent of agent B was intact on the roof at three minutes after application. At 30 minutes after application, 94 percent of agent A was intact while only 20 percent of agent B remained. For blower air in 3.3 m/s (650 fpm) ventilation, the results were dependent upon nozzle type. Three different nozzles were tested. At 30 min after application, 74 to 92 percent of foam agent A remained, while 3 to 50 percent of foam agent B remained. Compressed air foam seems to remain intact for longer durations and is easier to apply than blower air foam. However, more water drained from the foam when using compressed air foam, which demonstrates that blower air foam retains more water at the roof surface. Agent A seemed to be the better performer as far as roof application is concerned. This testing demonstrates that roof application of foam is feasible and is able to withstand a typical face ventilation velocity, establishing this technique’s potential for longwall shield dust control.

Jan 1, 2017

By M. R. Shahan, W. R. Reed, S. Klima, T. W. Beck, Y. Zheng

Testing was conducted to determine the ability of foam to maintain roof coverage in a simulated longwall mining environment. Approximately 27 percent of respirable coal mine dust can be attributed to longwall shield movement, and developing controls for this dust source has been difficult. The application of foam is a possible dust control method for this source. Laboratory testing of two foam agents was conducted to determine the ability of the foam to adhere to a simulated longwall face roof surface. Two different foam generation methods were used: compressed air and blower air. Using a new imaging technology, image processing and analysis utilizing ImageJ software produced quantifiable results of foam roof coverage. For compressed air foam in 3.3 m/s (650 fpm) ventilation, 98 percent of agent A was intact while 95 percent of agent B was intact on the roof at three minutes after application. At 30 minutes after application, 94 percent of agent A was intact while only 20 percent of agent B remained. For blower air in 3.3 m/s (650 fpm) ventilation, the results were dependent upon nozzle type. Three different nozzles were tested. At 30 min after application, 74 to 92 percent of foam agent A remained, while 3 to 50 percent of foam agent B remained. Compressed air foam seems to remain intact for longer durations and is easier to apply than blower air foam. However, more water drained from the foam when using compressed air foam, which demonstrates that blower air foam retains more water at the roof surface. Agent A seemed to be the better performer as far as roof application is concerned. This testing demonstrates that roof application of foam is feasible and is able to withstand a typical face ventilation velocity, establishing this technique’s potential for longwall shield dust control.

Jan 1, 2018

By M. Kuchta, S. Iverson

INTRODUCTION Underground blasting with perimeter damage control can reduce the requirement for loose rock scaling and reduce the risk of ground-fall injury. In previous work Johnson and associates (2010) from the National Institute for Occupational Safety and Health (NIOSH) developed a rock blasting perimeter damage and control design method included in the DRIFT software tool (NIOSH, 2018). This blast design software tool utilizes current methods of perimeter blasting with the added design element of a buffer row coordinated with the perimeter row to reduce perimeter damage. The coordination is in applying one of several blast damage models to calculate the damage extent for each production, buffer, and perimeter blast hole in the design. The calculated damage is then applied to the spacing between the blast holes. The basis of the buffer row design is the practical damage limit and is supported in this paper with computer models of signature blasts and full blast rounds using PFC2D (Itasca Consulting Group, Inc., 2018). Practical damage limit The practical damage radius (Rd) is not to be confused with burden. The practical damage extends toward the burden side and inward into the rock mass. For all practical purposes, the practical damage radius equals one half the burden (Hustrulid, 1999). The maximum extent of radial crack damage around a blast hole (Rcrack) and the maximum extent of radial crushing damage (Rcrush) are illustrated in Figure 1. A “practical” radius of damage (Rd) lies between the crushing limit and the cracking limit. The “practical” damage means that if the rock mass lying outside of the practical damage circle were removed, the rock remaining within the circle would easily break apart. Blast pressure and strain Work by Johnson (2010) and associates included signature blast tests in large concrete blocks. A signature blast test in concrete as exampled by strain data in Figure 2 was designed to monitor the dynamic strain at incremental distances from a single fully coupled blast hole, measure crushing and radial cracking extent by wire-sawing to expose the damage, and relate the damage to overbreak that is common in underground blasting. The initial slope or rising strain as the stress wave passes by the strain gages shows very high strain and strain rates close to the single blast hole. Since the derivative of strain versus time is strain rate, a line tangent to each of the strain curves at the maximum strain rate is drawn and the strain rates identified. The high strain rates were then plotted on a semi-log in Figure 3 to show a linear trend. The strain rate is greater than 100 s-1 within 20 cm from the blast hole for the signature blast experiment. The strain rate at the blast hole wall is projected to be 300 s-1. Figure 4 illustrates the damage in the NIOSH block exposed by a wire saw cut.

Jan 1, 2019