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By Z. T. Bieniawski, D. A. Newman

The Geomechanics Classijication (RMR System) (Bieniawski, 1979) was modified for entry and roof support design in underground coal mines. Adjustment multipliers were introduced to incorporate the influence of high horizontal stresses and the roof support reinforcement into the existing classification system. Sixty- two case histories of standing and fallen mine roof were collected from two mines in the northern Appalachian coalfield. Twenty-seven engineering and geologic parameters were recorded for each case. A partial correlation analysis was carried out on the cases to establish which parameters have a significant im- pact on the stand-up time of supported coal mine roof. Survival analysis, a statistical technique used in medical research to assess the effect of a drug or treatment on a patient's life expectancy, was conducted together with stepwise multiple regression to derive values for the adjustment multipliers. A practical example is included to illustrate the application of the modified Geomechanics Classification to underground coal mine design.

Jan 1, 1987

By P. E. Snoek, R. L. Gandhi, C. S. Miller

Slurry operations are an integral part of mineral processing. There is therefore reason to consider using slurry pipelines for long distance mineral transportation. This paper reviews the current state-of-the art of such systems and, in particular, the design factors which must be addressed. It also discusses the selection of major components such as pipe, pumps, valves and storage facilities. Finally, the major steps required to determine the economic feasibility of a slurry system are listed and the major advantages and disadvantages of slurry pipelines compared with other forms of land transport are summarized. SLURRY PIPELINES: GENERAL OVERVIEW Minerals Transported Long distance slurry pipelines have been successfully used for transporting coal, iron concentrate, copper concentrate, limestone and phosphate. Additionally, several tailings disposal pipelines of considerable size and length have been built, but these generally are not categorized as long distance commercial mineral transportation systems. Table 1 lists selected examples of commercial slurry pipelines.

Jan 1, 1986

By DeVerle P. Harris

The structure of an exploration model reflects a number of design considerations, one of which is the question or issue-to be investigated by the model. Thus, a model designed to evaluate the magnitude of risk and its economic implication to optimal decision making at each decision juncture of a multistage exploration architecture differs considerably from one designed to evaluate, say, the long run average cost of discovery, in which the architecture of exploration is suppressed and risk is simply an element of average cost. The perspective of the model examined in this paper is that exploration is investment in (purchase of) information and that the next stage of an exploration program is undertaken only when the expected value of information to be acquired in that stage exceeds its cost. The degree to which this perspective is honored influences considerably model design. Consider two design objectives:

Jan 1, 1989

By Trevor A. Moss

Installation of equipment and structures at mines often requires mine planners to evaluate unique loading and operating conditions. Consideration of these unusual features is required throughout design and construction and into operation. Most planners understand the necessity of employing sound civil, structural and mechanical engineering techniques to design these structures and equipment. However, the influence of geotechnical factors on the overall progress of construction and operation is less appreciated. Mine operators routinely perform exploratory drilling to define ore deposits. These exploration activities can be extensive and often include provisions for assessment of subsurface conditions as they relate to the mining operation - requirements for ground support. All of these factors are important to the economics of the mine and are well justified. Surface facilities are provided to access and service the mine, and they play an important role in the successful development and operation of a project. Headframes, hoist foundations and shaft collars, in particular, are examples of unique installations encountered at underground mine sites. The design and above-surface behavior of these facilities can be analyzed with the usual fundamental engineering practices employed throughout the engineering professions. However, near surface exploration for the purposes of assessing soil and rock conditions for foundations is often given a reduced priority and less consideration. This article provides an outline of the benefits and importance of performing such exploration. References here relate particularly to shaft headframes, hoists and shaft collars. But the issues raised apply equally to other installations of a similar nature, including milling equipment.

Jan 1, 1992

By Reinhard Gnilsen

Ground pillar control in soil and weak rock often represents a critical and sometimes a determining factor for mined underground civil structures. A concept is desirable that minimizes the restrictions possibly imposed by pillar control requirements on geometrical tunnel characteristics and on the mining operation itself. Conventional concepts are discussed and an alternative concept is introduced. This concept reduces pillar control requirements to ground control measures required with "regular" tunnels. The conventional model of pillar mechanics with potential yielding of a ground body in more than one direction, is then avoided. Due to the complexity of pillar mechanics, the level of engineered design furnished to the contractor is crucial to optimizing ground pillar control. Conventional versus alternative contractual arrangements for pillar control are described and their important role is illustrated. The concept introduced relates to principles inherent to the New Austrian Tunneling Method (NATM). However, tunnel projects using other mining concepts can employ alternative ground pillar control principles as well, if certain criteria are observed. Case histories in the United States and abroad are presented and the impacts from different concepts of ground pillar control are illustrated. The paper concludes by analyzing concept characteristics that can infer monetary impacts on both the owner and the contractor.

Jan 1, 1987

By P. H. Lu, M. J. DeMarco, J. R. Koehler

Beginning in late 1985 and continuing through 1987, US Bureau of Mines personnel investigated longwall chain pillar and entry design in two and three-entry gateroad systems at a deep underground coal mine in central Utah. To evaluate their respective stability characteristics, four chain pillars and two longwall panels within the two separate entry systems were instrumented with Bureau hydraulic borehole pressure cells to continuously monitor vertical and horizontal pillar and panel stresses through adjacent panel retreat. In addition, supplemental entry closure information was obtained from sites located in the vicinity of the instrumented pillars. The findings presented in this report demonstrate the practicality of evaluating mine pillar stability using in situ methods and support three significant conclusions regarding ground control aspects of the investigated two-entry system: (1) Total areal entry loading was considerably less for the two-entry system, as opposed to the three-entry system, (2) a smaller percentage of opened ground in the two-entry system contributed to a marked reduction in rooffalls, and (3) lower areal loading in the two-entry system suggests improved ground conditions when mining the underlying seam.

Jan 1, 1987

By John T. Bartlett

During the last decade, the increasing price of gold has renewed interest in the various metallurgical techniques for recovering precious metals. Much of the recent technology advance has been aimed at low grade deposits resulting in more complex processes and the necessity of tighter economic control. These factors along with more stringent environmental constraints have made it necessary to optimize each process to minimize energy and raw material consumption and reduce waste discharge. In most cases, detailed process analysis is required to detect inefficiencies and provide alternative solutions for process improvement. Also during this same period, the computer has become widely accepted and computerized mathematical modeling has been applied to an increasingly broader range of problems. Microcomputer based process modeling and simulation systems are routinely used to analyze and improve communition, hydrometallurgical, and pyrometallurgical processes for the recovery of precious metals.

Jan 1, 1987

The price of copper has gone into the tank. So has gold. Environmental regulations are more restrictive. Global warming has world leaders and environmental groups seeking international regulations to keep the planet from heating up - mostly by restricting the use of fossil fuels. And the US Secretary of the Interior wants to make it more costly -prohibitively so for smaller companies - to mine hard rock metals in the United States. By rights, miners should be carrying around a pessimistic attitude about their industry. But miners are an optimistic lot, always believing that things will improve. That optimism was in evidence in Tucson, AZ in early December, when about 620 miners met at the Double- tree Hotel for the Annual Meeting of the Arizona Conference, put on by SME. Attendees listened as a United States congressman commented on the recent tax cut bill, mining regulations and the continuing need for the mining industry to improve its image in the eyes of the general public. Session speakers discussed how improved technology has made their processing operations at Sierrita and Morenci more efficient and cost-effective.

Jan 1, 1998

By Sukumar Bandopadhyay

In recent years planning of surface mines in general and reclamation and post-mining land uses in particular have become very complex. Due to the lack of suitable techniques, land use plans are rarely based upon structured decisions. Data collection may be conducted in a rigorous manner and certain analyses may be performed on the data; the decision to put the land to a specific use, however, is finally based upon the intuitive judgment of one or several individuals. This paper demonstrates how techniques from fuzzy set theory can be used in order to select an optimum post-mining land use plan. The various land use planning alternatives have been characterized according to both qualitative information and quantitative factors and the "fuzzy" aspects of the collected information are incorporated into the analyses. In a practical application, the methodology is used to obtain the most reasonable solution to a post-mining land use planning problem in Interior Alaska.

Jan 1, 1986

By Mustafa Kumral

The study area is located in the Alpine-Himalayan zone in Turkey. Geologically, this is a very complicated region, and the rock units generally are divided into two groups as either allochthonous and autochthonous. Tectono-stratigraphically, the units are Paleozoic quartzite, black limestone, arkosic sandstone, interlaminated radiolarite and Triassic limestone, thick Jurassic limestone, detritic limestone with alternating Eocene Nummulites beds and cream-green marl, Miocene siltstone, and ophiolite. Trachyte, trachyandesite, feldspathoidal trachyandesite porphyry, tuff, and pumice formed by volcanism during the Plio-Quaternary also are present. Recent alluvium and slope detritus locally cover all the other rock units. A number of sulfur outcrops occur in the area. Among them are outcrops at Keciborlu, Yelliyatak Hill, Buyuk, and Kucuk Kukurt Dere. The most important sulfur deposits are found in volcanic tuff and siltstone-marl, and they include highly organic material. Sulfur may accumulate around recent gas diffusions and also as massive formations. The information about local geology and sulfur isotopes shows that the sulfur originated From the crust and probably comes from organic-rich Paleozoic and Triassic units. The sulfur did not move between Triassic and Pliocene time. However. Plio-Quaternary volcanism did cause movement of the sulfur, and this was followed by formation of the secondary sulfur due to post-tectonic thermal activities and the mixing of other surface waters.

Jan 1, 1999

By Patricio A. Espinoza, Aldo Casali, Cristian Ardiles, Guillermo González

Cluster analysis is used to design grade soft-sensors in a rougher flotation plant and a ball mill overload soft-sensor. Soft-sensors are virtual sensors which either replace unavailable actual sensors or infer measurements for non existing sensors. In the case of the grade soft-sensors clustering serves to determine clusters of related operating points. To each cluster there corresponds an ARMAX model structure whose parameters are estimated using only the points in the corresponding cluster. Thus a much better correlation is found than if all the data points were used for a global model. The problem of identifying clusters when the measurement of the real sensor is not available is addressed. In the case of the overload soft-sensor, variables were selected which are related to overload, either from a phenomenological point of view or according to operator experience. Different clusters are formed, some of which are identified as determining an overload condition or a possibility of such condition. Each of these clusters has a set of operating conditions which suggests the corrective action to be taken when necessary. Both kinds of soft-sensors are tested with industrial plant data and promising preliminary results are obtained.

Jan 1, 1995

By Richard R. Klimpel

This article introduces the basic definitions and philosophy behind process hazard evaluation procedures and the determination of risk as being a function of accident probabi1ity and accident consequence. The general concepts of good engineering practice and predictive hazard evaluation are discussed. The most commonly employed methods used in the processing industries are reviewed with an eye towards briefly presenting what each method offers as far as information, time and resources required, etc. Some initial references on the actual practical use of each technique in the processing industries are also given.

Jan 1, 1991

By Laurel E. Burns

Alaska is in competition with the rest of the world for exploration dollars. Providing a "seed package" of airborne geophysical data for the state's numerous mining districts encourages companies to begin more detailed exploration in more areas than they could have afforded on their own. When data are already available, the initial risk decreases for people involved in exploration. Airborne magnetic and electromagnetic data help ge¬ologists and geophysicists determine what rocks and structures are present under overburden and vegetation. These data form a fundamental package that exploration companies want before intensively exploring most regions. Individual mining companies have conducted their own geophysical surveys during the past several decades. However, these data are not available to other companies. The companies able to afford geophysical surveys have less money for ground exploration after purchasing expensive, private geophysical data. Therefore, they are not able to explore as many places as they might. Additionally, since data are not shared with other exploration companies, the proprietary surveys do not foster intercompany competition to move projects forward. Individual prospectors and small companies can not afford their own geophysical surveys. "It is more often than not the grassroots exploration efforts of the smaller operator that leads to significant discoveries," said Klaus M. Zeitler, senior vice president for development and exploration at Teck Exploration. Acquiring and releasing the geophysical data to the public produces several benefits. The increased explo- [ ]

Jan 1, 1998

By David J. Kruse

Although it may be perfectly acceptable to neglect the belt's elastic behavior for many conveyor designs, this can lead to disastrous consequences for others. So how can a designer know in advance if a dynamic analysis is required? Unfortunately, in many cases it is impossible to foresee or predict dynamic problems prior to performing the actual analysis. However, a basic understanding of the principles of conveyor dynamics, as well as knowledge regarding common problem areas, can significantly help the designer make more educated decisions during the initial design stage. This paper will demonstrate how static calculations alone can incorrectly represent the true behavior of the conveyor system. It will also discuss the importance of correctly sizing and locating the take-up system to provide the most economical conveyor design. The use of capstans will also be discussed followed by two examples demonstrating their proper operation.

Jan 1, 2002

By L. M. English, Y. J. Wang

When plotted as head vs. volume, fan curves start high and decrease with increasing volume, while mine head curves start low and rise with increasing volume. Their intersection is the system operating point. However, as every ventilation instructor knows, the fact that head loss is a negative number (debit) and fan head is an energy addition (credit) is often a stumbling block to student or audience comprehension since the curves seem to reflect the opposite. It is possible to use the intuitively correct curves- pressure losses as negative values and energy additions as positive values - and still obtain the correct operating point. Adding the two curves produces a third curve that intersects the x-axis at the operating point, the point at which the fan energy input exactly matches air circulation energy loss. Using this technique also makes it easier to account for outside influences on the system, such as natural ventilating pressure. With the standard approach, it is quite easy to add or subtract such influences to the wrong curve. This approach can be extended to the graphical solution of any series/parallel ventilation network. The results are the same, and the approach is logically consistent and less confusing.

Jan 1, 1999

By B. L. Gibbs

Computers have been used in the minerals industry for about 30 years and, in a few cases, longer. With the explosion of microcomputing during the past 10 years, computers have changed how many minerals producers go about their work. What computer usage trends are active in the minerals industry today, and what can we expect in the future? In general, computer usage is accelerating. Engineers and geologists are becoming increasingly "application literate." Soft¬ware is increasingly oriented to how people work. User interfaces have improved, so most users need to know only a mini¬mum of system commands and structure to work with a computer. Most industry professionals know how to use word processing and spreadsheet pro¬grams. AutoCAD appears to be the drawing program of choice. One reason is availability of training and add-on programs for earthwork, mapping, contouring, etc. Another frequently cited reason for using CAD is the ability to quickly make changes to a map or design, as compared to hand methods. Management is moving toward greater acceptance of computer usage. Computers do not need workman's compensation ... even though they may get sick and take a few days off! Computer hardware used in most minerals-producing companies is strongly personal-computer based and likely to remain so. The 486 personal computers are inexpensive as compared to workstations and provide the power and speed to run most applications in minerals industry engineering offices.

Jan 1, 1994

By Martha Caudill

When planning for the required amount of storage capacity at a proposed open-pit coal mine or determining when additional storage capacity should be added to an existing operation, the decision must be based on a breakeven- analysis relating the discounted cost of capital for storage capacity to the marginal costs incurred for additional crew call-outs on weekends and demurrage charges. The model developed in this paper uses simulation techniques applied to two coal mines in the Powder-River Basin to determine how much storage capacity is needed and when it is needed. The paper also generalizes the simulation model so that it can be applied to any type of open-pit mining operation. Two important results of the model are (1) all of the mines in the Powder River Basin have excessive amounts of storage capacity, and (2) management is provided with estimates of the total number of hours that crews will have to work on the weekends as annual tonnage increases, and the levels of demurrage costs incurred.

Jan 1, 1986

By B. E. Davis, D. A. Stanley, C. E. Jordan

A prototype expert advisor was developed by the U.S. Bureau of Mines to systematically offer advice on the control of a Florida phosphate operation. The PC based system receives input from remote sensors for circuit parameters such as feed rate, reagent addition, and pH and from operator entered information such as the quality of the concentrate and tailings in each of the coarse, fine, and amine flotation circuits. The computer evaluates the information using rules obtained from industry representatives and Bureau flotation experts. Recommended actions and questions are displayed to quickly guide the operator to a problem within the flotation circuit and suggest a solution. This process control system could provide more uniformity among the flotation operators and also serve as a trainer for new operators. In addition, it represents a step toward fully automated systems for phosphate flotation.

Jan 1, 1990

By Stanley M. Miller

Analysis of discontinuous rock masses for engineering design purposes requires information about fracture characteristics. For such studies, fractures or other elements of the rock fabric (bedding, foliation, etc.) should be considered in a statistical manner because they generally have high frequencies of occurrence and are discontinuous over the design area. A practical design procedure includes defining structural domains as those areas which contain fractures with similar orientation patterns. Within a structural domain, the statistical distributions of fracture set characteristics (spacing, fracture density, dip, dip direction, etc.) may be computed from mapped data and then used to quantitatively describe the rock fabric. These distributions can then be randomly sampled (using Monte Carlo techniques) to simulate the rock fabric and to help define potential failure surfaces along fractures. 1 The prediction of failure geometries is an essential part of stability analyses used in designing rock slopes or underground openings. In current probabilistic design procedures, Monte Carlo techniques that rely upon the iterative generation and analysis of deterministic instability models do not incorporate spatial aspects of the random variation in fracture set characteristics, 1,2 but consider the characteristics to be spatially independent.

Jan 1, 1979

By Changhong Huang, Y. J. Wang

This paper describes the formulation of mine ventilation network optimization as a standard nonlinear programming problem and the solution of the problem using the generalized reduced gradient (GRG) method. In general, the GRG method is regarded as one of the most effective and efficient methods for solving large-scale nonlinear programming problems. The variables considered in the network optimization include air quantity, regulator pressure loss, and fan pressure for each branch. Each of the variables is constrained by lower and upper bounds. This facilitates proper assignments of ventilation requirements and provides a great flexibility to include various situations encountered in mine ventilation. The objective of the network optimization is to minimize the overall air power consumed by or supplied to the network; whereas the constraints are, in addition to the variable bounds, the two fundamental network laws: Kirchhoffs voltage law and Kirchhoffs current law. A computer program has been developed based on the GRG method for the network optimization. An example of network with 18 branches, 8 regulators and 3 fans is included for illustration.

Jan 1, 1993