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By Nora M. Hutt, Kevin A. Morin

There is currently some pessimism over mixing of net-acid-neutralizing (NAN) and net-acid-generating (NAG) rock to obtain indefinite near-neutral seepage from mined-rock piles. This is due in large part to the lack of well- documented, successful cases of blending and layering, and to the knowledge of unsuccessful attempts. Past work often defined a potentially successful mix in terms of the ratio of net-acid-neutralizing rock to net-acid-generating rock. For example, one case study indicated the bulk pile-wide ratio was approximately 3: 1. Since this exceeded a common ratio used in acid-base accounting, no acidic drainage was predicted. However, acidic drainage appeared within two years. A large part of the ambiguity in mixing arises from attempts to predict success based on a ratio. This paper looks in detail at simple discrete-zone mixing, where at least one truckload of NAG rock is placed in a particular location with no further rehandling or dozing. The lack of acidic drainage in this scenario is dependent on the intervening distance between the discrete NAG zones, along flowpaths occupied by NAN rock. Calculations show that the bulk mixing ratio of a mined-rock pile is not an accurate indication of whether near-neutral drainage can be maintained. For example, a pile with a bulk ratio around 300: 1 could still release some acidic drainage. Calculations also show that the minimum separation distance of the NAG zones (L) can be so great, even with typical NAG and NAN rock, that the mixed pile could safely contain only a few percent of NAG rock, which would not be sufficient for many minesites with NAG rock. The comparison to a more elaborate, computer-based statistical model shows that the simple discrete-zone approach will provide a reliable yes-no indication of whether any acidic drainage will leave a pile. However, predictions of whether combined downstream drainages will be acidic depend on numerous site-specific physical and geochemical factors within and below a pile that cannot be modelled in a general way, like the number of flowpaths and the nature of their intersections.

Jan 1, 2000

My first regular job nearly fell through. My parents were spending the summer in California and I joined them at Lake Tahoe where we were guests at the lovely summer home of the Reids of Belmont. The time went quickly but I was eager to start work so I left for Bisbee a few days earlier than I had arranged. This was lucky, as just after I left a letter came from Gene Whitely, chief engineer of Calumet and Arizona, saying that because of the depressed copper industry there would be no job. I reached Bisbee on a Saturday morning, a day or two before my 23rd birthday, July 27, 1907. The brown plastei four-story Copper Queen Hotel was only a few steps from the station where the branch railway ended. I rented the cheapest room on the top floor and, of course, there was no elevator. I soon learned how to walk up the mile of switching tracks to the Calumet and Arizona office at the Irish Mag mine. I was horrified when Whitely told me about his letter telling me not to come, but since I had not received it he relented and said I could work for a short time anyhow. I was to start at 7:30 the next Monday morning, "holding the ignorant end of the tape”-in other words being surveyor's assistant, at $100 a month. Hours were from 7:30 to 5: 00, seven days a week. I spent Sunday walking around the town. I rented a room at the Royal Lodging House, which was cheaper than the hotel. It smelled strongly of carbolic acid but that meant no bugs. Compared with Cobalt or Cripple Creek, Bisbee didn't seem unattractive. The main street, with one or two-storied stores and saloons, followed the bottom of the canyon with high steep hills on both sides. My lodging house was on a rock in a narrow spot in the canyon, discouragingly called Tombstone Canyon. Chihuahua Hill, opposite the

Jan 1, 1976

By G. Davey

High speed stirred milling is a relatively new method of grinding in the metalliferous process industries. However it has been it has been in wide spread use in the industrial mineral field for over 30 years for various minerals. Many existing metallurgical operations are looking to maximize economic return from existing deposits, requiring new thinking and technologies. The operating experience of two existing copper operations will be covered to show the effect of the introduction of the Metso Stirred Media Detritor (SMD) a new type of high speed stirred mill. Both operations have derived significant metallurgical benefits from the introduction of this new technology. The benefits and process difficulties are covered and explained.

Jan 1, 2003

By Boris K. Krstev

INTRODUCTION The flotation process, in the real industrial complexes, is characterized by the existence of the significant number of the close reciprocal interrelationship between the input and output Darameters. Traditional complexity is appeared with regard to absence of the suitable a priori information for the physico-chemical characteristics of the flotation process. It’s led to needful of taking of consideration about the undefinition which have got the place in the real conditions and application of the statistical methods. The identification of the flotation process through statistical methods is conception of the more-stages procedure, including the collection and previous analysis, the choice of the model structure and valuation method, the estimation of the model un- known parameters and the results interpretation. The essential concept for the subject of this paper belongs to the empirical models ("black-box") and deals with optimizing in constant industrial plant process. The offered method envisages the application of process operation data in order to improve the work process or constant accomplishment of better results for the target function in relation to the former achievement. The optimum process solution isn't afixed value under the influence of various factors, but "a moving point" along the response surface and deviates from the scheme solutions. The evolutive planning method constantly "investigates and approaches" the optimum solution for the selected target function. As a matter of fact the expert operates the plant without interrupting the normal work process. The essential concept of method is to attain changes in the standard conditions, but so limited that they will not effect either production or the product. This method is based on statistical concepts and availability of following the risk of error. The possible influental factors for the flotation process (m=l, 2, 3) is following: the metal content in the feed ore; production level (t/h); grinding fineness in the flotation pulp; pH-values; the consumption of collectors and modifiers The possible target functions are: the recovery of plant capacity, metal recovery in the concentration process and concentration quality. The application of the evolutive operativity method in the chalcopyrite flotation- Bucim concentrator, combines the statistical data and the operator's experience in the interpretation and making a decision which adds up to the precise automatic performance of the process. The advantages of this method in relation to the existing procedure for the flotation process are the following: • The method is unexpensive and losses are reduced to the time necessary to collect the data and record them in the computer. This method provides a constant process control and a quality decision which is better than those brought by an ex- pert with great experience ("hit-and-miss method"). • The method also provides incidental data about the effects. • The method should not be considered as a procedure for solving an incidental problem ("crash program"). • The obtained results must be interpreted by an appropriate expert in order to be considered instructive. MATHEMATICAL STATISTICS Taking into consideration the complexity of the enrichment processes it's necessary the application of "black-box" and mathematical modelling. The presence of the indefinite elements compel us towards the both theory of the probability and mathematical statistics. The mathematical statistics by the mineral processing investigation of the valuable raw materials in the last years has had greater signifance and widely spread application. The application of the mathematical statistics methods for the technological pro- cess analysis and the construction of the mathematical models is bound up by the task putting of the automatic control system de- sign (Fisher R. A. 1941, 1949). The statistical analysis in the enrichment processes is applied formerly, especially in the sampling estimation. Contemporary, in the last years is imposed the tendency of mathematical statistics application for the obtaining of quantity characteristics and quantity valuation from the individual influental factors. Above mentioned tendency in the significant level is based by the mathematical statistics development as a mathematical discipline close connected with the technical cybernetics general joining to the investigated object as a "black-box". Another essential factor in the mathematical statistics development is appeared the created mathematical theory of experiments as a new, to some extent, autonomous statistical domain. The theory of experiments has demonstrated exclusively importance for the investigation of the complex more-factorial processes in the chemistry, mineral processing, metallurgy etc. The investigation by the enrichment processes of the valuable raw materials and their management is possible by the statistical method application. In the same time, it's possible to use the wide-spread traditional methods of the statistical analysis, such as the methods of the dispersion, correlation, regression etc. Also, it may be mentioned above all the methods of the statistical planning of the extreme experiments. The more perspective are representatived some cybernetic methods which are based by the probability as an approach in the process analysis, for example, the identify of the ways and forms, the graph application as an additional instrument in the correlation analysis, the dynamic programming etc. The mathematical statistics application in the laboratory investigation scale is connected above all by the experimented material analysis and the compact representation of the obtained results. The mathematical statistics methods are more varrying and may be applied in the investigations of the wide circle of problems

Jan 1, 1996

By James P. Connell

HISTORICAL BACKGROUND The American Concrete Institute defines shotcrete as "mortar or concrete conveyed through a hose and pneumatically projected at high velocity onto a surface." This definition thus includes what is traditionally known as gunite, which is a pneumatically applied mortar. In mining practice, the term shotcrete is restricted to pneumatically applied concrete, and this differentiation will be used in this chapter. In 1914, following the invention of the mortar gun in 1907, then chief engineer of the US Bureau of Mines (USBM) George Rice developed the gunite process for underground test work at the USBM facility at Bruceton, PA. After World War I, gunite was used extensively in American mines and was also utilized for underground civil works such as the San Jacinto tunnel in California. The greatest development was in Europe where, as early as 1911, gunite was successfully used as an overlay for deteriorated tunnel linings. In 1951, the Swiss firm Aliva developed a pneumatic gun capable of handling coarse aggregate, thus making possible the first use of shotcrete at the Maggia hydropower development. Initially, shotcrete was used to reduce manpower requirements for forming and placing conventional concrete. However, by 1954 Sonderegger was reporting that the structural advantages of shotcrete were derived from its flexibility and from the fact that it could be applied almost immediately after the opening had been made. The incorporation of wire mesh into the shotcrete led to the new Austrian tunnel method or NATM. The use of shotcrete in American mines has been implemented more recently. This delay seems to be due to previously unsuccessful experiences with gunite as a structural material and to the US reliance on wood or steel supports in main-line haulageways. The long experience with the apparently more substantial rigid supports led mine operators to be reluctant to accept the new and seemingly unrealistic lighter shotcrete support. APPLICATION REQUIREMENTS Shotcrete is a relatively new material for use in underground support systems. Consequently, experienced miners are not always available who are capable of applying the material effectively. Shotcrete, particularly in the small cross sections typical of mine shafts or haulageways, is applied in cramped quarters under less than ideal conditions. Adequate lighting should be made available. The surface should be clean and free of running or dripping water. It may be necessary to collect flowing water in plastic pipes or water collection devices. Any dry cement dust from previous shotcrete applications should be washed from the surface in order to assure a good bond. The US Bureau of Reclamation (USBR) while shooting test panels at the Cunningham tunnel in 1974, found that experienced shotcrete operators were able to obtain up to three times greater compressive strengths than were obtained by unskilled operators using the same equipment and shotcrete mix. ENVIRONMENTAL AND SAFETY REQUIREMENTS Since sodium and potassium hydroxide, as well as other moderately toxic compounds, are often contained in shotcrete (particularly where accelerators are used), safety precautions must be taken to prevent skin and respiratory irritation. Nozzlemen and helpers are required to wear gloves, protective clothing, and ventilation hoods with a filtered air supply. Respirators approved by USBM, equipped with chemical filters that will not pass the caustic mists, may be permitted in lieu of hoods if goggles or safety glasses are worn. Protective ointments are available to reduce skin irritation. All air and shotcrete feed hoses should be equipped with safety-type couplings and secured with safety chains at each coupling to prevent whipping in the event of a hose or coupling failure. Some environmental effects can take place down-stream from the development face being supported. The accelerator compounds, as well as the portland cement used in the shotcrete, will be found in the rebound material which falls to the invert of the heading. Since these compounds may be leached from the rebound material and carried by the drainage system, it may be necessary to install neutralizing or other water treatment facilities. Investigations may find that the final reaction with other compounds being leached from the mining operations may result in a more or less environmentally acceptable end product. USES OF SHOTCRETE General Uses Shotcrete, as a combination of cement, aggregate, and accelerator, is utilized for underground openings such as shafts, adits, haulageways, and service chambers for the following general purposes : (1) primary sup¬port; (2) final lining; (3) protective covering for excavated surfaces that are altered when exposed to air (the protective covering may be of a temporary or final nature); (4) protective covering for steel or wooden supports, rockbolts and rockbolt plates, heads, nuts, and other mats, including wire fabric, used to prevent rock-falls; and (5) as a lagging material in place of timber, steel, or concrete between steel or wooden supports. These applications can be grouped into three general use categories: shotcrete used as a rock sealant, shotcrete used as a safety measure, and shotcrete used as a structural support. Use as a Rock Sealant Thin applications of shotcrete can reduce or prevent slaking of shales or other rocks that are altered when exposed to the wetting and drying cycles created by mine ventilation circuits. While shotcrete may be effective in preventing such rock alteration, at the present time it is not as economical or efficient as other commercial sealants. However, if the sealant property can be incorporated into the structural support capability, the added contribution is usually helpful. Thin applications are not usually sufficient if the alteration of the

Jan 1, 1982

By R. A. Jankowski

Although the number of operating longwall mining systems has remained relatively constant, longwall production levels during the last five years have increased significantly. In the United States, longwall mining now accounts for approximately 50% of all underground coal production. While longwalls are highly productive and offer other advantages, operations employing this method of mining continue to experience dust-compliance problems. This increased longwall productivity has meant that far more dust is being produced. An improved understanding of the longwall face-ventilation system and the advancement of face-ventilation technologies are necessary to ensure all face personnel are allowed to work in an environment that is free of excessive levels of airborne respirable coal mine dust. The Dust and Toxic Substances Control Branch, National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, examined several basic principles of the long wall face-ventilation system and has evaluated the effectiveness of numerous improved face-ventilation techniques for longwall mining systems. These include identifying improved techniques for measuring face-ventilation parameters on longwall mining sections and investigating the fundamental relationship between face airflow and the entrainment and dilution of respirable coal mine dust. Studies have been completed to determine the impact on face dust levels of using belt entry air to ventilate the longwall. Novel methods have been identified to increase the face air¬flow and to manage face airflow to effectively minimize dust exposure to face workers. Unique systems of auxiliary face ventilation have been developed and evaluated at full-scale, simulated longwall test facilities. The theoretical and applied aspects of each of these principles and technologies are discussed. Application of these results throughout the longwall mining industry, as documented from surveys conducted in the early 1980s and 1990s, have reduced the health hazard associated with excessive exposure to respirable coal mine dust.

Jan 1, 2000

By Andrew Burton, Damian Schofield, Jeremy Noond

This paper will introduce and discuss a range of techniques that utilise new developments in Computer Graphics (CG) and Virtual Reality (VR) for the investigation of incidents and accidents in mining environments. The future of mining safety may not be totally led by the demands of the mine operators, but sometimes by the academics, commercial software developers and legal pioneers who generate new ideas and products and set admissibility precedents which may change the way certain traditional investigative operations are performed. In any accident investigation the outcome from the investigating team is often a complex affair and the results of the investigation are often reported in large, convoluted documents. Computer-generated forensic reconstructions allow investigators to present accident scenarios in an accessible and easily understood, visual manner. Surveys in the US have also shown that people have increased recall of computer-generated images over many other forms of evidence. The AIMS Research Unit in the UK have been pioneering the use of Computer Graphics (CG) and Virtual Reality (VR) technology for both industrial and road traffic accident reconstruction. This paper and accompanying presentation will contain examples of forensic reconstructions developed by the authors that explain some of the methodologies used to ensure admissibility of this type of digital evidence. The paper will contain a number of case studies based on UK and International industrial accidents. The paper will focus on how AIMS Research is extending the capabilities of the accident reconstructions created to take advantage of the latest developments in VR technology. As digital technology makes its impact within professional and commercial fields, computer generated forensic reconstructions will form important admissible evidence in the courtrooms of the future. The technology will also make a great impact in the way we train our workforces, with highly visual three-dimensional (3D) interactive training tools becoming the norm. Acceptance by the public, courts and workforce is an important issue, and implementation strategies must be considered carefully.

Jan 1, 2002

By John W. Scott

INTRODUCTION The design criteria for a particular concentration and dewatering project will provide the formal basis for design of the process, equipment and facilities. These criteria will specify the required capacities and operating schedules for the equipment, as well as the quantity and quality of the feed to be processed and products obtained. The general climatic and geographical conditions at the site, specific information on soil or rock conditions; and applicable design standards and codes will also be included. The design criteria will generally be based on an interpretation of testwork carried out on the particular ore and site, and will thus parallel in detail and completeness this testwork. As the project moves from the early conceptual phases through to final detailed design, the design criteria will be developed and become more detailed as information is generated and made available for use. The design criteria are critical to the design effort as the formal specification to the designer of what and how much is to be processed, what and how much is to be produced, and where and under what conditions. The actual design criteria will be a formal tabulation of the design basis information developed for the project in question. For a preliminary study, this may consist of a single page of data; for a feasibility study several pages and for a detailed design up to several hundred pages and multiple volumes. Depending on the complexity of the process and the level of detail included, each project will be unique to some degree. The design process for a project normally progresses from preliminary conceptual phases through to a final detailed design. The criteria used for the initial concepts are generally developed from rough data and preliminary testwork on the ore in question. Regardless, the plant throughput and products are defined, thus giving a scope and definition to the study phase. In some studies a range of throughputs may be analyzed in order to arrive at the most economically attractive size for the proposed operation. This optimum size is then used as the design throughput for the more detailed design phases. Similarly as more testwork results are available and the ore characteristics and process become more well defined a continuous updating of the design criteria is undertaken.

Jan 1, 1986

In spite of our deep conviction that it would be wrong for the United States to enter World War II, when, after Pearl Harbor, we were actually in it, I felt that I must do all I could to help. The country had been so good to me that I could not decently stay on the sidelines. My first thought was that I might help with supply and administration in the Air Force, as in World War I. So on the evening of Pearl Harbor I wired the chief of our Air Force in Washington saying that I had been on Gen. William Mitchell's staff in World War I and was offering my services again. I received a noncommital answer, but after a couple of weeks was told to take my physical examination. I passed it, but nothing further happened. After helping to make plans for the wartime operations of Summit King and Desert Silver, Dorothy and I went to New York to spend Christmas with Molly and Peter, both of whom were in college in the East. I had to complete a report on the Argonaut mine in California first, though the war made my recommendations of dubious validity. Before Christmas I received wires from Temple Bridgeman, Phil Wilson, and other friends who had taken positions with government agencies responsible for securing mineral products needed for war use. They urged me to join them. It was evidently a case of not whether but how I could be most useful. After six uncertain days with the family in New York I took the night train to Washington on the 28th of December. I had a hectic day there. First I saw Arthur Bunker and Phil Wilson at what became the Aluminum and Magnesium Division of the War Production Board. Their office was in an old converted barracks. They asked me to examine magnesium deposits in Nevada at once, and then to look at other magnesium and aluminum properties. After leaving

Jan 1, 1976

On my arrival in New York after the Russian examinations John D. Ryan, president of Anaconda, asked me what my plans were. I told him I wanted to be useful somehow in the World War that we had entered while I was away, but I did not know how. Ryan and Thayer told me that the new American Air Corps was gathering a group of executives, most of them young, to go to France as Army officers to help with the industrial side of our aviation activities. This would include construction of military airports, maintenance, and supply for our rapidly growing Air Corps. They thought I might be accepted in this group of about 30. It seemed to be just what I wanted, and I put in my application at once. My application was accepted about three weeks later and I was told to come to Washington to take physical and other tests and to meet others of the group. I liked them. They were a cross section of competent American manufacturers, bankers, automobile executives, and merchants. I was the only miner. I had many discussions in the days in Washington with members of our organization and others I knew who were going into war service. Attitudes were very different from those 55 years later. There was no discussion as to whether war was right or wrong. We were in it and must do all we could to help. At the same time there was a holdover from the days when, at least for the elite, war was high adventure. Even the most high-minded did not then realize that war is a horrible form of wholesale murder and, in 1917, it would have been treason to suggest this. I had two weeks before our industrial group was to start work which gave me time for a hurried trip to Berkeley where Dorothy and I announced our engagement.

Jan 1, 1976

By W. G. Pariseau

Regression analysis of calculated on measured displacements were used to assess the influence of fill and fold plunge on shaft pillar mining at the Homestake Mine. These effects were neglected in the original three-dimensional finite element analysis undertaken in 1991. An average fold plunge of 15? and a 24K fill (Young’ modulus of 24,000 psi or 165 Mpa) were used in the reanalysis. Measured displacements were obtained from an array of 36 m (120 ft) multiple-position borehole extensometers installed in June 1994 and read to March 2003. Results indicate the effects of both on calculated displacements and thus on regression parameters are noticeable. However, these neglected effects would not have changed the original inference of Ross Shaft stability during pillar mining.

Jan 1, 2004

By Jr. McCulloch

Mining operations of Freeport Indonesia (FI) are located approximately 4 degrees -6' south latitude, 137 -7' east longitude in Irian Jaya the eastern most state of Indonesia (Figure I). The mines are located approximately 96 km (60 miles) from coast in the Carstenz Mountain range. The ore bodies are between 2900 and 4000 meters (9500 and 13 000 ft) elevation.

Jan 1, 1989

By Scott G. Britton

Until now, only the range of typical construction projects which are repeated over and over during the life of a coal mine have been discussed. This chapter looks at underground construction projects which occur only once or twice during the life of any given mine and are major construction projects in both time and cost. These projects usually require the services of an outside engineering and construction firm with hands- on experience in design installation. Because of this involvement with engineering and construction firms (EIC), the role of the construction engineer will change from one of actively de- signing and directing tasks to one of planning, inspection, and quality control. To reflect this role change in the discussions, the focus of this chapter will be changed to a broad overview of project participation. Of course, the projects under consideration in this chapter could easily fill more than one book on their design and installation. In addition, major construction projects are extremely site specific, requiring months of data collection about site geology, physical conditions, and potential excavation and construction requirements. Therefore, no attempt shall be made to discuss any detailed construction aspects as was done in earlier chapters. The purpose of this chapter is to present the fundamental concerns of a staff engineer or supervisor. This engineer does not make the decisions on choosing the EIC firm, but assists and interacts with their project team to accomplish the goals set forth by higher management. The construction topics to be reviewed fall into three main categories. The first category is highlighted by the installation of a main surge bin; the second is typified by the construction of an underground shop; and the third category encompasses special projects such as rotary dumps, crusher stations, and foremen's offices. These categories highlight the differences between degrees of mine responsibilities for project completion. The first topic is usually a turnkey project by an E/C firm for a given mine. The second topic represents the leading role of the mine in the project with a contractor as a support service or equipment supplier only. The third topic, special projects, is an example of a joint venture-between a contractor (leading partner) and mine management. These roles can change with any given project, but the changes in management responsibilities for the construction engineer can be nicely illustrated for the purposes of this text. The first step toward constructing major mine projects is to analyze the mine which influence their design. From the mine management standpoint, these parameters should reflect the role the mine will play in the project construction. In other words, what is the nature of the proposed mine environment and what are the material, labor, and time requirements needed to assist or direct the chosen engineering and construction firm? Answering these questions requires some basic project planning and cost estimation work. Here, only a general treatment is necessary, since detailed discussions of these topics will follow in Chapters 8 and 10. For those persons interested in the role of the EIC contractor, I suggest beginning by reviewing the article by Beall, "The Role of an Engineering and Construction Contractor," presented in the October 1980 issue of Mining Engineering magazine.

Jan 1, 1983

By T. V. Durkin

Approximately 1,390 t (44.7 million ounces) of gold have been produced in South Dakota since 1875. South Dakota's mining laws attempt to strike a balance between economic development and environmental protection by promoting mining as an industry while requiring prevention of pollution and reclamation of affected lands to a beneficial use. The mining laws have evolved since their inception in 1971, especially in response to gold mining. The laws have remained flexible to meet changing regulatory needs. Gold production has continued relatively unabated, even in the face of public scrutiny, two mining moratoriums, and isolated environmental problems. The department's system of "one-stop-shopping" for environmental permits streamlines the permit process, fosters quick resolutions to compliance problems, and helps keep enforcement actions out of the courts. Specific case histories at heap leach mines within the Black Hills are presented.

Jan 1, 1998

By C. D. Mann

INTRODUCTION The sublevel stoping mining method is usually applied to a relatively steeply dipping, competent ore body, surrounded by competent wall rock. Ore is produced by drilling and blasting longholes, which can range from 50 mm (2 in.) to 200 mm (7% in.) diam, with lengths up to 90 m (300 ft). Longholes can be inclined in any direction, but the ring or pattern usually forms a plane, and the holes are blasted as a unit. Recently developed mobile drilling and loading machinery, as well as new explosives products, blasting techniques, and cemented sand and rock fill have made sublevel stoping a highly efficient and versatile mining method. When designing a sublevel stoping production sys- tem, it should be kept in mind that production rates from conventional sublevel stopes vary widely through- out the life of the stope. Early production is at a low rate, coming only from the drawpoints near the slot, but increases as new drawpoints are reached by the stope face. As the stope nears completion, again, fewer drawpoints are productive. Enough drawpoints must be available at any time to provide required production. Drawpoint availability should be compared to equipment availability; plan for more drawpoints than are needed at any one time. Accurate, realistic scheduling is essential to smooth production rates. Also, initial recovery of ore in a stope/pillar block is normally from 35% to 50% in sublevel stoping. Planning of pillar recovery, representing the majority of ore tonnage in a production block, must be done during early mine planning. Since much of the development already done for primary stoping (access for drilling, drawpoints, and haulageways), can be used for pillar recovery, early production from pillars is highly desirable. The following description of components of the system is an attempt to highlight some of the most important features and requirements of mechanized sublevel stoping methods. Similar comments would apply to the use of older equipment (column-and-arm drill setups, slushers, etc.) in similar methods. As in any good mining system, maximum economic recovery of the resource in the ground is the primary consideration. STOPE DESIGN CHARACTERISTICS Length and Width The following are some of the factors which affect sublevel open stope length and width dimensions: ore body geometry, principal stress directions, competence of stope back, optimum drill pattern, and drilling drift layout. In new mines initial stope layout design may occur before the ore body is actually intersected by mine workings. Stope dimensioning is a critical decision, and assistance from as many knowledgeable people as possible at this stage is essential. Operators with past experience in similar ore bodies, rock mechanics experts, and others with mine design experience should participate at this stage of stope planning. Height The following are some of the factors which must be considered in determining stope height: competence of stope pillar and stope/fill walls; slenderness ratio of adjacent pillars; ore body dip; ore body thickness; hole depth capability of the drilling machine; fragmentation characteristics of the ore; and level intervals in existing mines. In competent ground, drill-hole length and accuracy are the most important determinants of stoping height. Frequently entire drilling sublevels can be eliminated because of the depth capability of sophisticated drilling equipment, resulting in significant development cost savings. Drawpoint Location and Design Some of the most important considerations of a good drawpoint system are optimum spacing of draw- points, within the constraints of stope dimensions, for uniform drawdown and maximum recovery; excavations designed for stability for the life of the ore block to be drawn-primary stope ore as well as subsequent pillar ore; floor or roadway design including type of surface, reinforcing, grade for water runoff; orientation with respect to the main haulageway, for optimum loader maneuverability and ground stability at the inter- section; and length, to allow articulated front-end loaders to work in a straight configuration. Careful drawpoint design and construction are keys to successful production. Extra care in development, such as smooth wall blasting, rockbolts or grouted rebar, wire mesh, and shotcrete usually will ensure long draw- point life. Human exposure during production loading is of longer duration than during development or production drilling, and consequently preparation of draw- points is easily justified, particularly when pillar ore can be drawn through the same drawpoints. Secondary blasting of boulders can weaken drawpoints, also justifying good ground control techniques. A smooth draw- point floor of poured, reinforced concrete, on a grade of +3% or +4% toward the ore pile facilitates water flow out of the drawpoint, and ease of loader bucket penetration into the muck pile. Slot Raising, Slotting A slot or other space for rock expansion is necessary in conventional sublevel stoping where vertical rings or rows of holes are blasted. The slot can be started at a slot raise driven by conventional raising methods, raise boring, drop raising (predrilling and blasting a raise from the top, using small diameter-less than 200-mm (7%-in.)-holes for relief), or crater blasting (similar to drop raising, but without relief holes). The slot usually extends from the extraction level to the back of the stope. It is normally expanded to full stope width by

Jan 1, 1982

By J. B. Gwiazda

Maintenance of a constant load setting throughout longwall support units and selection of the proper initial bearing capacity depending on the type of roof strata are the basic factors that ensure good performance of roof support in a longwall. These requirements can only be met by hydraulic support. The greatest advantage of hydraulic support is achieved when uniform pressure is imposed on the roof throughout the length of the longwall. Such support, however, is provided only if each of the support units acts with the same force against the roof, i.e., has the same setting load. In such cases, the roof behaves like a uniform plate without bending and shearing stresses, thereby ensuring an undisturbed structure. Without a positive set value system, achieving an equal setting load for all units of the longwall support is impossible. Due to alterations of the feed line pressure of support units as well as some reasons related to man's psychology, operators extend the height at different setting loads. This produces nonuniform roof stress, and disturbs the structure. Consequently, the roof usually cracks. The author has developed a positive set value system, which is described in this Technical Note. Selection of the setting load Two pressure values in the feed lines are usually applied in longwall hydraulic systems. Lightweight support is fed by 25 MPa (250 bar) liquid, while heavy duty units receive a nominal pressure of 31.5 MPa (315 bar). Such pressure is required not only for the props but also to power the adjust¬ment jacks and the advancing ram. If the feed pressure is too low, there will be difficulty in shifting the unit despite the inversion system of the advancing rams. On the other hand, for many roof types, the feed pressure often appears to be too high when applied as the setting load pressure. An excessive setting load acts too strongly against the roof, crushing weak strata close to the roof. The author has recognized a case where an excessive setting load destroyed not only the nearby roof strata but also the strata above a 2-m (6.6-ft) sandstone layer. In addition, an excessive setting load relieves the side¬walls, increasing the resistance when using cutting machines. As a result, the yield of coarse coal is diminished, and increased fines dominate in the final product, lowering its economic value. As indicated, selection of the proper setting load, depend¬ing on the mining and geological conditions of the extracted seam, is extremely important. In some mines, measures applied to prevent disturbances include reduction of the feed line pressure by adjusting the feed pump valve. The disadvantage accompanying reduced feed line pressure is more difficult operation in advancing the ram. Due to the reduced feed line pressure, the force of the advancing ram is much lower than the designed value. Other designs suggest using a third feed line. However, installation of supplementary valves on the support units is required, a time-consuming and expensive procedure. The disadvantages of the powered supports are eliminated by a system designed by the author. So far, such a method of setting load control has not been used in any type of support. Setting load control unit The designed positive valve set for prop loading and the setting load control correspond to existing control systems for hydraulic powered support. The layout of the unit connected to the hydraulic prop control is presented in Fig. 1. The unit is marked LIDS. It incorporates three valves that may operate separately or connected. Valve A automatically opens and closes with liquid flow in the prop feed circuit. The valve is opened when the canopy touches the roof and closed when the support unit is withdrawn. Valve B serves as the setting load control. Valve C automatically opens and closes the flow in the line connecting the under-piston space of E to the prop F with the separator G. The valve block of each support prop is marked BZ. The UDS unit is connected by the hydraulic lines to the F prop control circuit. A valve is connected by H to pressure line J and by K to the G separator. In the UDS-3 version, line L is connected to M, linking the over-piston space of F prop with the G separator. Valve B is linked with valve A by a connector; it is also connected to the under-piston space E of prop F by line P. Valve C is fixed between lines K and P, connecting space E of prop F with the separator G. When setting the support, the liquid flows from line J through separator G, the BZ valve, and valve C to the space E of prop F. When reaching the roof with the canopy, valve A is opened and C closes. In this way it is impossible for the operator to cause the liquid pressure in space E of prop F to reach the level of line J. The prop pressure is set by valve B of the UDS unit. When withdrawing the support, valve C is automatically opened and A closed. Three UDS units have been fabricated and are designated

Jan 1, 1990

By Peter Van deVelde

Many companies in North America because of economic or environmental reasons are considering reprocessing material from their waste ponds. The Japanese have developed highly specialized machines and techniques to reprocess industrial/mining wastes from settling ponds. This paper discusses the techniques and results of applying this technology to North American applications.

Jan 1, 1983

By Q. X. Yun

This paper presents a new approach to optimize the transportation system in open-pit mines. The new approach employs artificial intelligence, fuzzy sets, dynamic programming and CAD technique to determine the transportation system. The determination consists of 4 phases: initial selection, road alignment, final decision .and open-pit drawing.

Jan 1, 1992

By D. A. Stanley, B. J. Scheiner

The Bureau of Mines, US Department of the Interior, has investigated the use of rheology to provide insight into the mechanism of flocculation. A technique developed by Tattersall has been modified and used to explain the flocculation of calcium montmorillonite with polyethylene oxide. The results indicated that there are two types of bond systems operating during the flocculation sequence. Also, flocculation results are highly dependent on the shear rate and the amount of polymer added.

Jan 1, 1990

By William J. Francart, Gary J. Wirth

Fire detection capability in conveyor belt entries of coal mines has advanced considerably since the passage of the Federal Coal Mine Health and Safety Act. The advances in instrument technology and computer based monitoring have provided better fire detection than ever introduced in the industry. This paper discusses recent belt conveyor fires and detections in mines utilizing CO Monitoring Systems. Data from investigative reports is presented on belt entry fires from 1991 to the present.

Jan 1, 1993