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The authors have succeeded in providing additional rigour and clarity to the formulation and execution of the dynamic programming algorithm for optimum open pit limit determination. The inclusion of the blocks on the J + 1 column in the search for Pmax, and constraining this search with blocks assigned a value of negative infinity, ensures an optimal solution within the defmed blocks. The effect of the negative infmity blocks is to preclude mining along the diagonal blocks from the first row that they occur in. Figure 1 graphically illustrates the effects of this on the calculation of P. A practical application for constraining mining with negative infmity blocks is the case where the pit outline is defined by lease boundaries and not by the value of blocks to be removed. Any legal, social or physical constraint could be accounted for in the same way.The danger in applying this technique is that the negative infinity blocks will override any other more profitable solutions that may exist. This is in fact what has happened in the example that the authors use. If a further column is added to the left hand side (column -1) and the calculation is carried out again, a more optimal x-section can be found. (If the negative infinity values are removed the same result is obtained.) This gives a pit value of 112 as against the 108 of the authors' optimal pit. This calculation is shown in Figure 2. Lerchs-Grossman optimization is reliable only if there are sufficient columns available to allow "mining" to optimum depth of the ore body and still allow the pit to break out at the surface within the confines of the columns.This author's approach is to create enough columns each side of the lateral limits of the ore to allow the pit to intersect the surface while still within the confines of the block model. Implementing the methods discussed by the authors helps to reduce the number of columns required to achieve this.

Jan 1, 1987

By J. E. Tobey, David R. Mitchell, J. H. Kerrick

DETAILED knowledge of purchase specifications established by coal consumers is essential to the successful design and operation of a coal-preparation plant. ANTHRACITE Specifications should be considered by both the consumer and the producer as guide posts outlining a certain path for both to follow. Plants differ, therefore specifications must differ to meet the varied requirements. Specifications are not of themselves a "cure all" or an assurance of complete satisfaction in fuel utilization. Specifications should not be regarded as a license to engage in an orgy of buying any and all coals that may happen to fall within their limits. This would lead to the indiscriminate mixing of coals which may vary in their burning characteristics. Different coals of equal grade tend to be individualistic in their burning characteristics. Rather, specifications should be used to help simplify coal selection, to reduce the actual number of coals used over a given period; in other words, to have a stabilizing influence on coal or customer turnover. In the final analysis, the use of too many coals per year in a plant is costly to both the consumer and the producer. Too many sources usually result in higher operating and maintenance costs for the consumer and higher sales costs for the producer. Finally, the statement included in the report accompanying the com¬prehensive Coal Selection Charts prepared by the Coal Committee of the National Association of Purchasing Agents, and released in 1938, is significant. This Committee worked diligently for a period of 15 years seeking to find a scientific and reliable method for selecting coals. The two following paragraphs are quoted from its report: More important is the fact that no ready-made classification or set of specifications can possibly replace the judgment and resourcefulness of an experienced combustion engineer or fuel technologist, nor the usual need for full scale plant tests under the exact conditions of use before a final decision is made ...

Jan 1, 1943

By J. P. Van Kleunen

9.3-1. Introduction. The demands of industry for handling materials at higher rates and at reduced costs have had a very significant effect on belt conveyor technology. Although the general appearance of the belt conveyor today is essentially the same as it has been for the past several decades, the similarity ends there. Each component comprising the conveyor system has been continuously improved through design and materials technology to enable present conveyor systems to operate at ever-increasing rates and reliability. For example, twenty years ago the strongest commercially available, fabric-reinforced conveyor belting had a tension rating of 50 lb per ply-in. Currently, fabric-reinforced belts are available with ratings of 350 lb per ply-in. and steel cable reinforced belting is available with tension ratings of 3000 lb per in. of belt width (3). These technological advances have therefore enabled the belt conveyor to not only attain acceptance as a preferred method for in-plant movement of bulk materials, but also to be used for long distance transportation of bulk materials, particularly in areas of adverse terrain. The information contained in this chapter is intended to assist the reader to make basic decisions regarding the use and application of a conveyor system. The design of an overland conveyor transportation system or an in-plant process conveyor is accordingly beyond the scope of this article. Many comprehensive technical works covering the design of a belt conveyor are currently available from the manufacturers of materials handling equipment (6, 7, 9, 11). The design handbook published by the Conveyor Equipment Manufacturers Association is particularly recommended (2). 9.3-2. Conveyor Capacities. One of the most important factors in determining the proper size of a conveyor system is the rate at which material must be handled. Although tables and charts are available to the conveyor designer to assist him in his selection of conveyor components, only the

Jan 1, 1968

This report presents the comments of members of the Institute's Sub-committee on Physics of Mine Ventilation on the proposals of a special committee of the Institute of Mining Engineers (London). This report is as follows: THEORY OF MINE VENTILATION Abstract of a report submitted June 16, 1925, to the Council of The Institution of Mining Engineers by a Special Committee Laws of Flow of Aib The law of flow of air in mine galleries is, at present, expressed by two formulas differing slightly in shape but both derived from the original hydraulic formulas of Chezy and others. These formulas are: The Atlcinson Formula.—Pa = KsV2, which in transformation becomes a3 where P = pressure producing flow; K = coefficient of friction; s = surface of the mine galleries; V = velocity of flow; Q = rate of flow; a = area of mine galleries. This formula is especially applicable to mine galleries, but is unwieldy in application, as in many problems we are dealing with changes produced in the same set of airways when K, s, and a are assumed not to change, and the only variables are P and Q. Great uncertainty prevails as to the exact values to be assigned to the coefficient K in different types of airway, as different workers have given widely differing values. This formula assumes: (I) That resistance to flow is independent of the pressure within the gallery. (2) That changes in volume within the limits of pressure ordinarily met with may be neglected. (3) That changes in density and viscosity and mode of flow of the air may be neglected. (4) That the coefficient K is a constant. (5) That P is proportional to the square of the velocity. We cannot find any reliable experimental work leading us to conclude how far these assumptions are justifiable in mining practice. Equivalent Orifice Formula.—The fundamental form of this formula is Q = ~nA.\/2~11

Jan 1, 1927

By M. A. Scheil, S. L. Hoyt

About three years ago eight standard steels were prepared for the cooperative investigation of methods for oxygen analysis, sponsored by the Iron and Steel Division of the American Institute of Mining and Metallurgical Engineers and by the National Bureau of Standards. A preliminary report of the results was made at the annual meeting of the A.I.M.E. in February, 1936. † This report showed the reliability of vacuum-fusion methods and further brought out certain advantages of the fractional vacuum-fusion method. The results obtained by the authors with the latter method will be discussed here, with some comments on the procedure for those who are interested in determinations of gases in steel. Some additional comments are offered on the use of the polarizing microscope for identifying the inclusions in the steel to check and amplify the findings of the fractional vacuum-fusion analysis. For details of the fractional method, see the paper by L. Reeve1. Degassing the Crucible One of the sources of error in vacuum-fusion methods has been the blank gases evolved from the graphite crucible after preliminary out-gassing. We have used 1750" C. as the outgassing temperature. This gives a base pressure at that temperature of less than 0.030 mm. after one hour and of 0.004 mm. on dropping the temperature to 1575" C. At lower extraction temperatures the base pressure is 0.001 mm. at 1050" C., 0.002 mm. at 1170" and 0.003 mm. at 1320' C. Because of the size of our induction coil we are limited to this temperature, although it 'would be advantageous to use 1950" to 2000" C. Hamilton2, after outgassing at 1850" C. for 100 min., was able to reach a base pressure of 0.001 mm. for a temperature of 1700' to 1725" C. This would give a blank corresponding to less than 0.00015 per cent 02 and 0.00005 per cent H2. Chipman and Marshall outgas at 2000" C. for one hour by using a special construction

Jan 1, 1937

By William E. Brewster

Dating back some five years ago, various foundries made inquiries as to the probable total carbon content in a given specification and grade of pig iron. Up to that time we had no data, and except for a few occasional determinations of total carbon, no attempt had ever been made to set up routine determinations of total carbon. In fact, at that time, a cast analysis was considered sufficient, without examining at further length into possible variations of analysis between ladles of the same cast. In view of the various inquiries as to total carbon, we sampled all piles of all grades of pig iron, making complete analyses. Finding some variation in carbon content, we secured more samples and plotted the carbon content with respect to silicon in each grade of iron except for the higher phosphorus foundry iron, where it was necessary to divide the group into twenty-point phosphorus ranges. This is easily understood, owing to the falling off of carbon content with the increase in phosphorus content, silicon in each case being the same. In addition, these curves clearly demonstrate the lowering of the carbon content as the silicon is increased. In order to insure accuracy and reliable determinations the following method of sampling and analysis was employed: Two pigs selected from each end of the car, each car containing iron from one 50-ton ladle, are drilled with a 5/6-in. drill all the way through from top to bottom in the center of one section of the pig. The drillings are collected and transferred to an 80-mesh sieve; the portion passing through and the portion retained are placed in separate envelopes and labeled accordingly. The amount of sample in each envelope is weighed to obtain the proportionate amount of coarse and fine drillings, then a 1/2 factor weight of sample (1.3636 grams) made up of proportionate

Jan 1, 1936

By C. A. Heiland

THE investigations described were made on a portion of Clear Creek basin near Golden, Colo. (A portion of the area under survey is shown in Fig. 1. The photograph was taken in the vicinity of station No. 2 of Line II.) Three principal purposes were in the minds of the investigators: 1. To repeat with modern, more sensitive and more reliable instruments magnetometric placer investigations previously made. 2. To disprove the recently advanced theory that deposits of the glacial period have no pronounced magnetic effects. 3. To develop in detail the theory of the magnetic effects produced by placer deposits. Six years ago, the first magnetic observations were published, which proved that it is possible to locate gold-bearing channels with relatively crude instruments.1 Two years ago, K. C. Laylander published results obtained with similar instruments.2 The measurements of the latter were discussed by the senior author of this paper.3 At that time, however, the material available for such a discussion was somewhat scarce and not made with the most modern magnetic instruments, although very brilliant results were obtained. Therefore, the senior author felt that magnetic investigations should be made on very clear geologic conditions with the most modern instruments.

Jan 1, 1928

By Alwan M

At Binebase mineralisation is hosted within an andesitic Neogene volcaniclastic succession on Sangihe Island, Indonesia. Two major alteration types occur; an initial widespread phyllic assemblage of quartz -illite with chlorite, smectite, gypsum and pyrite, and a superimposed quartz - barite - sulphide assemblage. The phyllic alteration arose from a neutral to weakly acidic hydrothermal solution of greater than 200 degrees C, and the quartz - barite - sulphide assemblage arose from a cooler slightly more acidic fluid. This second alteration event is interpreted to have selectively replaced permeable volcaniclastic breccias and coarse lithic tuffs within the altered sequence. Gold and silver mineralisation is associated with the latter alteration, and is locally controlled by the degree of silicification and sulphide abundance. The sulphides present are pyrite, covellite and chalcopyrite. The sulphides are very fine grained with colloform and framboidal textures and were deposited contemporaneously with the bulk silicification of the coarse sediments. A large portion of the mineralised rock has been oxidised to a quartz - barite -limonite - goethite - jarosite assemblage.Coincident gold, silver and antimony geochemical soil anomalies gave the best correlation with anomalous gold and silver grades in bedrock as identified by drilling. Resistivity proved a reliable geophysical method for delineating zones of silicification.

Jan 1, 1990

By Charles L. Kimbell

The concept of data availability must be addressed, because there are perceptible changes from year to year, and the availability of accurately reported, precisely defined statistics and nonstatistical information provides the only sound basis for analytical studies required for government policy planning or industry market analysis. As the countries of Eastern Europe and the former U.S.S.R. undergo the transition from centrally planned economies to market economies, there has been a perceptible increase in information availability for rather obvious reasons. Any industrial operation seeking economic assistance from Government and/or private sources outside the country in which the facility is sited must provide some appraisal of its operations at the time it seeks assistance, as well as some information on previous performance to serve as tools in evaluating its potential under the proposed development scheme for which it seeks financial assistance. Additionally, there was growing governmental recognition that concealment of much of the national mineral production, trade, and consumption data for purposes of national military and/or economic security probably never was very successful, never was really necessary for most commodities, and certainly proved unnecessary with the end of the so-called cold war. Indeed, the long-term unwillingness to publish uniform statistical series of reliable,

Jan 1, 1993

By M. L. Pearce

A comparison of the isotope-dilution, vacuum-fusion, and chemical methods of analysis for nitrogen in Si-Fe is made with particular emphasis on the effect of sample history. The superiority of the isotope-dilution method from the point of view of 1 HE analytical techniques used to determine nitrogen in Si-Fe have been subjected to close scrutiny in recent years primarily because of the marked influence of the element on the properties of the alloy. These investigations have led to a diversity of opin- both precision and accuracy is demonstrated. The solubility of nitrogen in 3.06 pct Si-Fe is investigated and the effect of silicon content on the activity coefficient of nitrogen is derived. ion regarding the reliability of the vacuum-fusion and chemical methods of nitrogen analysis when applied to si- Fe.'-' A majority of workers appear to favor the vacuum-fusion method over chemical methods particularly in those cases where part of the nitrogen may exist as silicon nitride or the total nitrogen content is very low. Contrary views have been expressed, however,' and it has been demonstrated that for some Si-Fe alloys both methods yield results which are significantly lower than those

Jan 1, 1963

By Richard J. Mainiero, Marcia L. Harris, James H. Rowland

In the past several years, there have been a number of blasting-related carbon monoxide migration incidents. In each case, there have been some common factors that appear to be related to carbon monoxide migration. Geology, heavy confinement of the blast, close proximity to the affected structure, and open pathways into the affected structure are just a few. Prince William County, VA is an area undergoing a boom in suburban development. In the year 2001, more than 4,050 new homes were constructed within the county.1 In the new housing development located in Bristow,VA, trench blasting was utilized to excavate proposed sewage and utility lines. On November 8, 2002, a trench blast was conducted for the installation of utility lines. Later that evening a carbon monoxide detector alarmed in a nearby house. The gas company and fire department sampled for carbon monoxide and measured 100 ppm and more than 200 ppm on the first floor and in the basement respectively. Subsequent efforts to prevent migration of CO into the nearby homes met with mixed results. The only reliable technique for protecting neighbors from CO appears to be the placement of CO monitors in the homes. The events are presented and discussed.

By Milton Williams

It is generally recognized that fluid is lost from rotary drilling muds to permeable strata during normal drilling operations;1,2-3 but that this fluid is the filtrate from the mud, rather than the mud itself, has been shown by various workers.1,4,5 The presence of this filtrate in oil-bearing or gas-bearing strata is undesirable and harmful. The decreased permeability of the stratum to oil effected by the presence of water has been pointed out by several investigators,6,7 and since, in the production of the reservoir fluid, the greatest pressure drop occurs immediately adjacent to the borehole, it follows that infiltered water is particularly objectionable in this region. Again, this filtrate tends to make electrical logs less reliable, since oil in the proximity of the borehole is probably flushed out to an appreciable extent by the water.8 Observation of side wall cores may be misleading for the same reason. Drill-stem tests in low-pressure areas may be of doubtful value where no oil is recovered, unless sufficient time is allowed for production of water lost from the mud. The infiltered water may hinder drilling operations by softening shales and causing sloughing; the ['tight hole" occasioned by excessive deposition of filter cake in the hole is a common occurrence. The filter cake remaining on the face of the producing formation may itself sometimes be detrimental to production.9 In view of these implications of the importance of filtration of mud, an investigation was undertaken to determine the factors involved in the infiltration process, and to correlate these in such a manner that the values obtained in routine filter tests employing a conventional filter of the "wall-building tester" type,10 together with data on size of hole, drill pipe, and rate of mud circulation, could be used to estimate water loss and distance of penetration of the filtrate into strata. Quantitative relations of filter-cake permeability, filtrate viscosity, and rate of filtration have been developed for filtration in the simple laboratory filter.4a,11,12,13 It is obvious, however, that the conditions

Jan 1, 1940

By Milton Williams

It is generally recognized that fluid is lost from rotary drilling muds to permeable strata during normal drilling operations;1,2-3 but that this fluid is the filtrate from the mud, rather than the mud itself, has been shown by various workers.1,4,5 The presence of this filtrate in oil-bearing or gas-bearing strata is undesirable and harmful. The decreased permeability of the stratum to oil effected by the presence of water has been pointed out by several investigators,6,7 and since, in the production of the reservoir fluid, the greatest pressure drop occurs immediately adjacent to the borehole, it follows that infiltered water is particularly objectionable in this region. Again, this filtrate tends to make electrical logs less reliable, since oil in the proximity of the borehole is probably flushed out to an appreciable extent by the water.8 Observation of side wall cores may be misleading for the same reason. Drill-stem tests in low-pressure areas may be of doubtful value where no oil is recovered, unless sufficient time is allowed for production of water lost from the mud. The infiltered water may hinder drilling operations by softening shales and causing sloughing; the ['tight hole" occasioned by excessive deposition of filter cake in the hole is a common occurrence. The filter cake remaining on the face of the producing formation may itself sometimes be detrimental to production.9 In view of these implications of the importance of filtration of mud, an investigation was undertaken to determine the factors involved in the infiltration process, and to correlate these in such a manner that the values obtained in routine filter tests employing a conventional filter of the "wall-building tester" type,10 together with data on size of hole, drill pipe, and rate of mud circulation, could be used to estimate water loss and distance of penetration of the filtrate into strata. Quantitative relations of filter-cake permeability, filtrate viscosity, and rate of filtration have been developed for filtration in the simple laboratory filter.4a,11,12,13 It is obvious, however, that the conditions

Jan 1, 1940

By M Biesinger, R St C Smart

Diagnosis of the surface chemical factors playing a part in flotation separation of a value sulfide phase requires measurement of the hydrophobic and hydrophilic species that are statistically different between the concentrate and tail streams. Statistical methods, based on the monolayer-sensitive time of flight secondary ion mass spectrometry (ToF-SIMS) technique, have been developed towards this ultimate aim by measuring hydrophobic species (collector ions, dimers and metal complexes, polysulfides) as well as hydrophobic metal ions, precipitates and added depressant species. Reliable identification of specific mineral particles is central to this statistical analysis. A chalcopyrite/pyrite/ sphalerite mineral mixture conditioned at pH 9 for 20 minutes to study transfer of Cu from chalcopyrite via solution to the other two mineral surfaces, since this mechanism can be responsible for their inadvertent flotation in copper recovery, showed no statistical difference in the copper intensities on pyrite and sphalerite (selected from Fe and Zn images) after this conditioning. Principal component analysis (PCA) identifies combinations of factors strongly correlated (positively or negatively) in images or spectra from sets of data. In images, PCA selects these correlations from the mass spectra recorded at each of 256 ¦ 256 pixels in a selected area of particles. In the image mode, PCA has proved to be a much better method of selecting particles by mineral phase with clearer definition of particle boundaries due to multi-variable recognition. It has clearly separated a statistical difference in copper intensities between the sphalerite and pyrite phases. The PCA method has been applied to concentrate and tails samples collected from the Inco Matte Concentrator demonstrating extensive CuOH and NiOH transfer between the chalcocite (Cc) and heazlewoodite (Hz) minerals. Statistical differences illustrate the important discriminating depressant action of NiOH in flotation despite the activation of Hz by Cu transfer. The adsorption of the collector at specifically-identified Cu sites has been elucidated by the study. Importantly, the statistical analysis has been able to confirm some mechanisms and deny others proposed to control recovery and selectivity giving more focus on the control factors.

Jan 1, 2005

About 74% of global seismic energy release occurs in the Circum-Pacific zone. Worldwide, about 71% of seismic energy release is in the form of shallow earthquakes, 27% as intermediate, and 2% as deep earthquakes. Seismic energy release is variable in time and has been shown to correlate with the amplitude of the Chandler wobble. It was high during the period 1949 to 1967, and is now at a rather low level, with the latest earthquake over M = 8.0 having taken place in Indonesia in 1971. The average worldwide recurrence rate for the expected largest magnitude earthquake (M "9.5) has been estimated as several tens of years, in marked contrast to the several tens of thousands to hundreds of thousands of years separating the largest volcanic eruptions. Geological studies are needed to establish reliable mean intervals between large earthquakes, and to detect the e;:istence of long-term fluctuations in the ste of occurrence. Seismic gaps have proved seful in static forecasting of large earthquakes, by identifying places where closer study of the variation with time of seismicity, deformation, and other parameters, may lead to the dynamic p_ediction of time, place and magnitude of earthquakes. The model of stress concentration at asperities explains the main features of seismicity in the Circum-Pacific. Slow earthquakes have been detected instrumentally, notably an event immediately preceding the 22 May 1960 Chile earthquake, the largest this century. It seems likely that this type of deformation may explain both instrumentally detected and macroscopically observed pre-seismic deformation, as well as unusual animal behaviour reported before some earthquakes. Seismic and volcanic events are interdependent, with large earthquakes commonly triggering eruptions. Melting of rock and intrusion of magma is likely to accompany many earthquakes.

Jan 1, 1987

By Tapio Ahokainen

Commercial modeling software and increasingly efficient computers enable today computational fluid dynamics (CFD) to be used as a tool for a more comprehensive understanding of the flash smelting and flash converting processes. CFD modeling can be used for design purposes in many technological areas, but some relevant physical and chemical phenomena are still missing in the commercial CFD solver packages. Therefore, Outokumpu has developed several subroutines for solvers to describe analytically the phenomena in the flash smelting environment. CFD sub-models of the copper concentrate and matte combustion, the particle-particle-wall interactions and for more accurate radiation properties of the gas-particle suspension are needed to ensure reliability of numerical simulations on the flash smelting and converting vessels. Several basic combustion phenomena can be modeled with a number of commercial solver packages, but own models for combustion must be included in the case of sulfides as the feed. Mathematical models for copper concentrate and solid matte combustion have been developed during the last decade. They calculate compositions of the particles and temperature, based on extensive experimental research work in laboratory scale furnaces with validated kinetic parameters and temperature measurements of reacting particles. Inside and near the concentrate burner, the standard particle tracking methods do not include the particle-particle interactions and the particle-wall interaction is too much simplified to describe properly the particle collisions with the distribution cone. Therefore, additional models for the particle-particle as well as particle-wall interactions have been written and implemented. For thermal radiation, models for the emissivity of a gas mixture and for calculating the particle absorption and scattering coefficients have been developed and tested. In addition, the advanced radiation model can be used i.e. in the enhanced simulation of off-gas cooling in the heat recovery boiler area of the flash smelter.

Jan 1, 2006

By Gordon Thompson

"Development of the unique Mine Games exhibition at Science World British Columbia is the largest ever collaboration of many interests to present the story of mining and the issues of mineral development delivered to the public by a science education centre.IntroductionMineral education programs have long been a major focus of the British Columbia mining community. Mine Games and its tremendous potential to enhance industries image and the public's awareness of mining is unequalled in the field of Issue Based Education Exhibits.The main goal of the exhibition is to look at the future of resource industries in a rapidly changing world of economic activities, new technologies, and growing public concern for the environment. Three challenges were the aim of the exhibition: to increase participation, to serve as a tool to increase interest in science and technology, and to draw an increasing number of school students to the interests of geology and the earth sciences. Mine Games is to serve as a meeting place for discussion of issues and where reliable information can be shared and new ideas explored.The exhibition is designed to develop new approaches to hands on learning that encourages visitors to explore and generate discussion and thinking with respect to resource development activities.The role of author, beginning in 1993, was, with senior industry leaders, to coordinate the raising of $1.3 million to complete the funding of the $1.6 million project total. The second and most interesting challenge was to work with the many minds that were collaborating to create the exhibition and to assure that the facts and science were correct. This involved the coordination of ""expert groups"" that verified the science and technology and the issues that the creative design team at Science World planned to use in development of each exhibit module."

Jan 1, 1995

The control system of a mine winder or other variable speed drive has many component parts that must work together to provide the required functional performance of the machine, together with comprehensive safety features, reliability, maintainability, user-friendliness and efficiency. Modern winders use digital control technology extensively and hence software design is a major part of the overall system. It is not practical to simulate an entire mine winder in a single computer model because of the sheer mathematical complexity of the behaviour of many of the components. However, most component parts can be simulated quite easily, and related parts of the control system software can be simulated. Such simulations allow control software algorithms to be developed and tested in isolation from the real plant. Tests can be performed on the model without fear of injury to personnel or damage to the valuable plant. For example, speed regulator control algorithms and stability settings can be adjusted to and beyond the limits of stable operation, and near optimum settings can be found. This is particularly important, for example, when designing closed loop controls for emergency brake systems. Obviously, care must be taken to ensure that the computer model of the plant is realistic and takes into account as many non-linear features of the real plant as possible. Pure mathematical analysis of some systems is very difficult to perform when non-linear plant behaviour is involved. This paper shares a number of practical simulation experiences performed using commercially available software such as Matlab and Simulink to simulate various parts of the control system of a mine winder or other variable speed drive. Demonstrations of the operation of several different computer models are shown during the presentation of the paper.

Jan 1, 2005

By Jida Wu, Zhenqian Wang, Chusheng Liu, Wenqiang Qiu, Mengqi Zou, Wei Zhao

During the dry screening, the hole plugging is a serious problem for most traditional screening equipment sieving the moist fine coal. It would lead to the low preparation efficiency and the low screening efficiency. The flip-flow screen is a new kind of screening equipment by using flip-flow motion of elastic screen surfaces to implement the separation of material. With the remarkable advantages of the extraordinary vibration intensity of screen surface, the hole is difficult to be plugged, and the screening efficiency is improved. In this paper, a kind of centralized forced flip-flow screen (CFFS) was proposed based on the crank rocker mechanism. The flip-flow motion of elastic screen surfaces is achieved by the periodical reversed motion of inner and outer screen boxes driven by crank. The advantages of the CFFS include considerable deformation of the screen surface, stable flip-flow quantity, low working noise, low vibration influence on environment, etc. The principle and construction of the CFFS were introduced, and the modal analysis and harmonic response analysis of key components (the crank and the linkage) were implemented based on finite element method (FEM), respectively. The first six orders of natural frequency and vibration modes were obtained. The maximum equivalent stress and strain under working and resonance frequency were achieved. The results illustrate that the resonance frequency is much higher than the working frequency, and the stress and strain are all within the safe limit of the material. The prototype was manufactured, and the sieving experiment demonstrates that the CFFS perform steadily, and screening efficiency is over 80%. The new feasible method of the dry screening was proposed by the CFFS. The corresponding numerical simulation and the experiment provided a reliable basis for the future promotion of similar product design and research.

Jan 1, 2017

By Stuart M. Lipofsky, Norm Hutchins

The Metropolitan Water District of Southern California has undertaken the Lake Mathews Outlet Facilities project to replace the existing outlet facilities. In the late1990s, consulting engineers for the District determined that the Lake Mathews Outlet Facilities were susceptible to a catastrophic failure during a seismic event. To ensure a reliable supply of water to Metropolitan’s customers in the Los Angeles area, the District decided to construct new outlet facilities. This Project consists of excavating a large diameter junction shaft, a 6.10 m (20 ft.) horseshoe tunnel, three short 4.88 m(16 ft.) horseshoe bypass tunnels, and a large excavation within a cofferdam that were all driven in difficult rock conditions. Additionally, a new concrete outlet tower was constructed and connected to the existing tunnel by the new bypass tunnels and through the junction shaft. The J.F. Shea Co., Inc. of Walnut, California, is currently finishing the construction of the Lake Mathews Outlet Facilities Project for Metropolitan. The large diameter junction shaft is 50.60 m (166 ft.) deep, excavated 16.15 m (52 ft.) in diameter and lined with a61 cm (2´-0?) thick steel reinforced concrete lining to a finished diameter of 14.63 m (48ft.). The shaft was excavated full face with one stationary shaft three-boom jumbo, modified for the large diameter. The shaft also consists of four sets of gate guides extruding from the shaft wall towards the center of the shaft that provide the ability to operate up to four mechanical gates at any time, to open or close each tunnel. This paper will present the junction shaft excavation and concrete construction techniques, including the innovative slip form method utilized to construct the junction shaft.

Jan 1, 2003