Search Documents

By Kevin Beauchamp

In many cases traditional support designs cover the many variations in ground conditions and bolt performance by a conservative factor of safety. The result is that most bolts are ineffectual most of the time and yet the response to occasional roof collapses is an even more conservative design. The probabilistic analysis presented in this paper takes several important parameters of a support design into account such as span, bolt strength, bolt length, water pressure, seismic accelerations, joint orientation, bed thickness and joint strength and allows the effect of variations in these parameters to be evaluated simultaneously. The analysis demonstrates the application of the probabilistic approach to both blocky, wedge-dominated conditions and bedded deposits dominated by laminations. All mine excavations have a designed stand-up time. By taking into account of the possible variations in the design parameters explicitly, it is possible to produce a support system designed to ensure stability over a given period of time. Rather than use a factor of safety criterion, the approach uses a percentage reliability or probability of failure. By understanding the probability of failure of the support system, it is possible to improve the performance of ground support without any increase in cost or conversely to decrease the cost while maintaining the performance of ground support. This approach reduces reliance on empirical experience and leads to a better understanding of the key factors that influence stability and can provide a much more accurate and optimized assessment of support design and performance. The result is a more cost-effective support system and we hope that a broader application of this approach to ground support in underground mines will lead to a greater acceptance in the industry of probabilistic analyses and of terms such as Probability of Failure and Reliability of Support.

Jan 1, 2003

By Rieniets S, Somerville J. L

In Morwell Open Cut brown coal mine, the overburden 'firehole' materials which have resulted from ancient coal fires vary-from hard baked clays to firm laminated lacustrine clays. The need to pre-strip designated areas to reduce the slope height and attain safe digging conditions for the bucket wheel excavator operation is now accepted practice at the open cut mine. In this study, the inherent spatial variability of undrained shear strength of the clay materials has been incorporated in a visco plastic, finite element based, probabilistic slope stability analysis. Data on the costs of initial pre-stripping, excavation and slope failure are collected to provide an economic basis for the optimisation of the design of the overburden batters in Morwell Open Cut. This improved stability modelling is enabling costly pre-stripping to be minimised while ensuring acceptable slope stability conditions and minimising the risk to personnel and plant.

Jan 1, 1994

By Kenneth L. Myers

The net balance of the inflow and outflow of water in a tailings storage facility has major economic implications in any large mining and milling operation. In a net precipitation environment it can control the ultimate size and storage capacity of a facility or dictate the need for an expensive treatment and discharge program. In a net evaporation environment it can control the extent of the water rights acquisitions required for makeup water and dictate the number and size of expensive wells and pumping and delivery systems. The elements considered in a water balance analysis include the anticipated production rate, the water content of the slurry used to deliver the tailings, inflow from precipitation and snowmelt, and losses from evaporation and seepage. The mine can exert significant control over only one of these elements: the production rate. All others are subject to considerable uncertainty from month to month and year to year. The traditional approach is to analyze in a spreadsheet environment by making simplifying assumptions and using monthly mean or "average" values for precipitation inflows and evaporation losses. Often the analysis will be repeated with values subjectively assigned to represent a "wet" year or "dry'' year. The probabilistic approach uses the same basic spreadsheet model in conjunction with a probabilistic simulation add-in program allowing probability distributions to be substituted for any of the deterministic variables. The resulting analysis shows the full range of variation possible for each parameter of interest (i.e., available return water, makeup water required, storage, seepage losses) and estimates the exceedance probabilities for each. The potential uses and advantages of the probabilistic approach are discussed.

Jan 1, 1992

By A. D. S. Gillies

The provision of a suitable working environment in deep level mines requires the accurate prediction of the ventilation heat load. Mathematical models for predicting strata heat load have been under development since the 1930's and 1940's. Computer models for predicting this and other mine heat sources have been developed and refined over the last 20 years. Some empirical studies have occurred and there is an increased emphasis on the importance of underground studies. Any theoretically or empirically determined predictive method must of necessity make assumptions. Underground space with its irregular configurations and rough wall surfaces cannot be described by simple mathematical expressions. Some heat loads, such as machinery, may occur intermittently while others such as the influence of water evaporation are very difficult to quantify accurately. Current popular models for predicting mine heat load have been surveyed. In testing some of these it is often found that each estimates significantly different quantitative values for the expected load in a particular underground space under study. These differences are explained by the assumptions, simplifications and omissions implicit in each of these models. It would be easier to estimate conditions at any point if heat flow into mine air passageways could be described by simple equations with associated statistically-based confidence ranges. Use of probability distributions to indicate confidence ranges allows any heat level estimate to be expressed as a range of values with limits for maximum and minimum expected values. This approach allows many of the limitations of the popular predictive models to be overcome. A heat prediction method using this approach has been developed based on Monte Carlo simulation and tested on mine data from a number of operations. Heat flow levels which can be predicted by simple equations supported by probability distributions allow the engineer flexibility in adjusting a predictive model to the underground characteristics appropriate to the mine site under study. The influence of all heat sources present in the mine opening must be included. Prediction methods must be updated as mining systems and machinery change with time. Heat sources interact with one another and the system must therefore be understood in its entirety.

Jan 1, 1987

By Alan R. Cameron, William Forsyth, Tom H. Kleinel

Because good and bad blasting must be defined in terms of overall mining costs, blast optimization requires combined blasting and costing models. Furthermore, the models must be both accurate and comprehensive. A combined fragmentation and preliminary costing model was developed to investigate alternative blasting strategies.

Jan 1, 1995

By Lawrence Bbosa, Aubrey Mainza, Indresan Govender

"Positron Emission Particle Tracking (PEPT) and the Discrete Element Method (DEM) are used to develop a probability based model for the power draw of a tumbling mill. Experiments are conducted using dry spherical glass bead charge in a laboratory scale tumbling mill, which is mounted with a torque transducer and tachometer to measure mill power. Particle tracking information from PEPT is used to reconstruct the motion of glass beads and infer the overall charge behavior, while DEM is employed to simulate particle motion and interaction, with collision mechanics calculated using the Hertz-Mindlin contact model. For both sets of data, the product of torque and average angular velocities in discrete cells are accumulated to obtain mill power. This method is found to be within statistical agreement with measured power for all tests. The information from both techniques is then used to develop a model for the power draw as a function of particle size, mill speed and volumetric filling. Predictions of the model match well with measured and calculated values. The model is found to predict mill power within close agreement with measurement and follows trends consistent with existing work on tumbling mill modelling."

Jan 1, 2014

Discussion of the paper of F. M. Simonds and E. Z. Burns, presented at the New York Meeting, February, 1913, and printed in Bulletin No. 75, March, 1913, pp. 369 to 402. W. L. SAUNDERS, New York,. N. Y.:-Mr. Burns in his native Colorado modesty has said that he apologizes for things left out of this paper. I am much impressed by what he has put into the paper, as of all the papers that I have read on the subject, describing, as it does, a specific piece of work that has been accomplished, I do not recall one that gives so much information in such a practical way. Mr. Burns has also said that it is very hard to get men to put things down while the work is being driven. My experience is that it is very much harder to get the men in charge of work of this kind to bring them in in the form of a report before a body of engineers after the work is done. We have a great many cases where records are kept in much detail, but they are usually kept under cover, with the mistaken idea that the information gained is private information for the benefit of those who have done the work. Messrs. Simonds and Burns have opened up this case so that we can get the benefit of that experience which they have had, and so that we can learn something for the future. The description contained in this paper, as I have said, is a very practical one. You will notice in going through it. that the authors have given in detail a record of their work from the beginning to the end, and they even go so far as to publish an exact copy of the Rawley Mining Co.'s daily report. That daily report is something which those of us who are engaged in similar work might copy to great advantage, and having it before us we can check up our men while doing work and exact from them equal conditions, if it is possible to do so.

Jan 5, 1913

By L. D. Ricketts

AN older man looks back, perhaps wistfully, on a long and rather active experience, and possibly a popular and brief glimpse of some contrast between past and present may hold your attention for a few brief moments and prove useful. In the late nineties an engineer was .called on to de- sign and build two copper ore concentrating mills of 400 tons average daily capacity. There were larger mills than this at Washoe and elsewhere, but a 400 ton' mill was a large one as mills went over thirty years ago, and one might say a large mill of those days could crush a ton of copper ore in 216 seconds. In the mills I refer to steel construction and the conveying belts were introduced into the copper industry and rein- forced concrete came shortly after. Since then we in the West have ever been faced with a constantly de- creasing tenor in the grade of our copper ores and a constantly increasing demand for our product, and we have therefore been obliged to call for far larger castings and finished machines than were formerly used. The mechanical engineer has also enabled us to accomplish notable economies in power generation and distribution. Ore handling and crushing have been simplified and through the introduction of reagents to induce physical or chemical reactions, or both, our older methods have been vastly improved or even supplanted by new and better ones and our recoveries greatly improved.

Jan 1, 1929

Part of a four-year course in metallurgy, dealing with metallurgical process engineering, was designed for students to acquire knowledge and skill from physical science, metallurgy, process engineering, and social science. Principles of education, and guidelines obtained from a study of professional practice, indicated that students may learn effectively through a planned sequence of problem-solving exercises based on the diverse functions of metallurgists in industry. The more important characteristics of the curriculum and a few illustrations of the problems are included. An outline is given of the current procedures used to develop parts of the curriculum, and of the students' diffic- ulties and achievements.

Jan 1, 1984

By Ali Akbar Mottahedi

Chromate conversion coating is a process for making a complex layer at the surface of zinc galvanized steel which makes the metal more resistant to corrosion, especially at marine atmosphere, and increases the adhesiveness of color. In this work the influences of various compositions on commercial zinc galvanized steel sheet to the color of chromate conversion coating has been investigated at normal temperature and the factors that affect the control and optimization of the process have been determined. A bath composition of 20 g/liter Cr203 and 10 g/liter NaOH and a dipping time of 50 seconds at room temperature (25-30°C) make a desirable color of chromate coating. A slow agitation at a constant pH of I (with additions of NaOH or H2SO4) assures a constant bath condition and develops the color. This kind of coating has more corrosion resistance and this bath condition and composition are also more economical.

Jan 1, 2003

By S. K. Kawatra, H. L. Dilley, W. W. Wen, T. C. Eisele

To improve the sulfur-rejection capability of a coal-cleaning plant, it is first necessary to evaluate the performance of the existing circuit. This information can then be used to decide whether there would be significant benefits from improving the operation and control of the existing circuit, or whether further improvements would require more radical process changes. This paper describes a simple model for evaluating heavy-media separation circuits, and presents a case-study of such an analysis of an operating heavy-media coal cleaning plant. Efficiency curves were calculated and modelled using Lynch's method, and a simplified expression was derived for calculating the Ecart Probability value from the model parameters.

Jan 1, 1995

By R. Hogg, T. F. Dumm

"It is generally agreed that dust characteristics play a role in the development of Coal Workers' Pneumoconiosis (CWP). Unfortunately, there is a serious lack of information on what the characteristics of mine dust actually are and how they vary among different mining regions, coal seams, etc. This paucity of data can generally be attributed to the serious problems encountered in collecting sufficiently large quantities of dust for conventional analytical procedures.Personal samplers are widely used in coal mines for regulatory and enforcement purposes. Generally, these provide information only on the total (respirable) dust loading in the mine atmosphere and on the mineral matter (primarily quartz) content of the respirable dust. A procedure has been developed by which samples collected with a slightly modified personal sampler can be analyzed for particle size distribution, total mineral matter content and elemental composition, in addition to the standard mass and quartz measurements. These analyses could readily be performed on a routine basis. Shape analysis by Scanning Electron Microscope (SEM) could easily be included if appropriate shape criteria are established. Extension of the procedure to include the determination of complete size/specific gravity (composition) distributions is quite straightforward provided sufficiently large samples (at least 10 mg) can be collected. Typical sample sizes for a personal sampler carried by a miner for one shift range from about 0.5 to 2 mg.The basic procedure was developed and evaluated using synthetic mine dust prepared in the laboratory. Field tests in three working mines in Pennsylvania and West Virginia have confirmed the applicability of the approach to the real world. Particle size distribution measurements on mine dust collected in the modified personal sampler were found to agree closely with the results of simultaneous in situ measurements obtained using cascade impactors."

Mar 1, 1989

By Y. J. Wang

This paper describes a procedure for solving the generalized system of n network equations in n unknowns considering the following ventilation variables and parameters: (a) air quantities, (b) pressure losses or gains caused by the control devices (i.e., fans or regulators), (c) resistance factors, (d) natural ventilation pressure, and (e) fan pressures (as a function of air quantities). The air quantities and pressure losses for all branches in the network are grouped into dependent and independent variables. The branches with an independent quantity are contained in a chord set, and the branches with a dependent pressure loss are contained in a chord set. In addition to the problem formulation, the solution procedure, applying the Newton method, is discussed and illustrated with a numerical example.

Jan 1, 1989

By James Marsh

INTRODUCTION Economists have long expressed suspicion of the economic theory of natural resource exhaustion, even in writing articles which have contributed to it (1). Indeed, the gap which separates the pure theory from practical management seems unusually wide. It is doubtful whether a mine manager could possibly know enough about the relevant parameters of his mine to steer it along the optimal paths described by the theorists (2). Nevertheless, enough faith in the theory remains that mine managers are suspected of being a separate breed whose behavior must be studied in special courses using specialized text-books, collections of readings, and journals (3). The implied hypothesis, that mines and natural resource firms are managed differently than other firms, is the subject of this paper. In the next section the theory is developed and analyzed. In section III, I discuss the implications of the statistical results that have been obtained. Finally, conclusions are reserved for section IV. THE MODEL A key difference between the traditional theory of natural resource production and that of other forms lies in the set of variables which ire assumed to jointly determine the quantity of output the firm will produce. Output, in the non-resource case, is assumed to be a function of k clearly definable and distinguishable inputs or factors of production, viz., y = f(xl, x2, ..., xk), (1) here

Jan 1, 1977

By C. L. Schneider, R. P. King

The ability to predict the liberation spectra that will be produced by a closed-continuous grinding circuit is of fundamental importance for the design, optimization and control of most operations in an ore dressing plant. The only known approach through which such a calculation can be performed is the population-balance-model equation. The latest, and certainly most significant, advance made in this area is the solution proposed by King (1990), which requires one textural parameter measured directly from the ore being studied. The main advantage of King's solution is that, unlike the conventional solutions, it does not require the estimation of hundreds of arbitrary parameters that cannot be independently measured. However, King's solution relies heavily on a knowledge of the detailed internal structure of the Andrews-Mika diagram (Andrews and Mika, 1975), which has never been measured for any ore. The characterization of the internal structure if the Andrews-Mika diagram requires the measurement of the liberation spectra at several progeny sizes produced by the breakage of monosize-monograde particles at several different grades. In this paper, a procedure based on magnetic fluid fractionation for generating seven narrow-size, narrow-grade samples is presented. Each of these samples was then broken into six progeny size classes in an ultrasonic mill. The one- dimensional liberation spectra of each of the 42 progeny and seven parent particle samples were then measured by image analysis. The measured linear-grade distributions are presented in this paper. The calculation of the correspondent volumetric-grade distributions is discussed.

Jan 1, 1995

By Ted Klemetti, Gabriel Esterhuizen, John L. Ellenberger

"Advanced numerical models can be used to evaluate entry support systems in coal mines. However, these methods require specialized software and specialized skills to create the models and evaluate the results. Practicing support design engineers require a method to rapidly assess a proposed support system for a given geotechnical scenario. A prediction equation that can be used to assess roof support systems has been developed from the results of hundreds of FLAC3D analyses that were conducted during recent research. These models were validated against field cases and empirical design approaches and were found to adequately predict entry stability in coal mines. The understanding developed from the model outcomes was used to develop an equation to predict entry roof stability against large roof falls. Least-squares error analysis was conducted to find appropriate parameters for the nonlinear equation. The developed equation can be solved using spreadsheet software, allowing for rapid assessment of alternative support system performance in variable geological conditions. The performance of the prediction equation is evaluated against empirical design methods and against selected case histories of support practices at currently operating mines. Examples are presented that demonstrate the performance of the equation in variable geological settings. The stability factor (SF) prediction equation can be used as an assessment tool to assist in the design of coal mine roof support systems.IntroductionGround falls represent a significant proportion of injuries and fatalities in underground coal mines in the US. During 2013, ground falls were responsible for 4 of the 14 fatalities and 16.6 % of the 1,577 reportable lost-time injuries (MSHA, 2015). In addition, each year about 400 to 500 large roof falls are reported that can extend up to or above the bolted horizon. Large roof falls and associated ground fall hazards can be mitigated through improved support design.The research presented here particularly addresses the problem of large roof falls that extend more than 90 cm (3 ft) above the roof line of an entry and may extend above the bolted horizon. Smaller roof falls that fall out between supports or extend less than 90 cm (3 ft) above the roof line are excluded. These smaller roof falls can be controlled by appropriate surface support such as roof screen or other skin control methods. Also excluded are roof falls that are associated with an individual geological structure such as a slip of fault. Structure-related instabilities can be controlled by strategically locating individual roof bolts or other supports appropriate for the local situation."

Jan 1, 2015

By Joao Felipe Costa, Jair Carlos Koppe, Alexandre Grigorieff

Discrepancies in raw materials properties informed by both producer or consumer is a common problem in most areas of the industry. Commercial contracts in the mineral industry normally penalises the producer, if contaminants in the ore exceed established limits. In some situations, the supplier is penalised if the quality of the ore is below a contracted amount. Differences in lab analysis are due many sources of error, such as distinct practices used in two laboratories for sampling, preparation or analysis. Rigid contracts impose to the miner the use of rigorous quality control program and in these situations sampling plays a major role. Sampling theory provides the tools to analyse errors involved in sampling, preparation and analysis. This paper proposes a methodology to check the precision and accuracy of a given sampling protocol emphasising the application of Gy's sampling theory to broken ore. A procedure to measure the error on each step of the protocol is introduced and the results compared to the fundamental error measured by Gy's theory. The results show the applicability of the method and its relevance to audit sampling procedures aiming at error minimisation. The methodology is illustrated in a case study at a major coal producer in Brazil.

Jan 1, 2002

By J. A. Barrera-Godinez

Traditional batch flotation tests produce a limited number of data points from which to evaluate the kinetics of the process. In this research, continuous weighing of froth, from a modified circular flotation cell, using a computer/data acquisition system., has been coupled with chemical analyses from intermittent froth sampling. This combination has permitted the experimental data to be smoothed such that the flotation kinetic parameters could be determined with enhanced confidence. To demonstrate the procedure, a galena ore was floated to permit flotation kinetics to be investigated as a function of cell parameters. It was shown that the kinetic data of this lead flotation most closely correlated with the Huber-Panu three parameter model. In addition the results illustrated the effect of froth thickness, froth scraper rate and air flow rate on the cell performance, in terms of mass flow, grade and recovery.

Jan 1, 1990

By Bora Derin

This work deals with the recovery of valuable metals from the ancient copper smelting slags located in Küre-Turkey. In this process, copper and cobalt were recovered in metallic form and/or as their compounds, whereas iron was recovered as magnetic oxide or pigment. Abrasive grit material was produced using reduced final slag. The process stages involved carbothermal reduction in a DC arc furnace, granulation, leaching, chemical precipitation, selective sulfidizing roasting and product preparations. In this paper, the process stages were described as theoretically and experimentally whereas slag and products were characterized in detail.

Jan 1, 2003

By Bora Derin

This work deals with the recovery of valuable metals from the ancient copper smelting slags located in Küre-Turkey. In this process, copper and cobalt were recovered in metallic form and/or as their compounds, whereas iron was recovered as magnetic oxide or pigment. Abrasive grit material was produced using reduced final slag. The process stages involved carbothermal reduction in a DC arc furnace, granulation, leaching, chemical precipitation, selective sulfidizing roasting and product preparations. In this paper, the process stages were described as theoretically and experimentally whereas slag and products were characterized in detail.

Jan 1, 2003