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By William Bergeson

This paper presents the challenges of the Homestead Avenue Interceptor Extension (HAIE) project in downtown Hartford, Connecticut. The new 72-inch (1,830 mm) sewer pipeline project consists of installing approximately 3,010 linear feet (920 m) of PVC lined reinforced concrete pipe using pressurized face microtunneling. The entire alignment is located within soft to very soft, varved silt and clay. To the extent possible, the alignment was selected to avoid bedrock, glacial till, miscellaneous fill,buried steel piles, and utilities. Challenges for this project include low ground cover, crossing major transportation routes, and limiting settlement to prevent damage to historical buildings and critical utilities. The machine was selected for the ground conditions. Design calculations were performed for selecting the reinforced concrete pipe class and for evaluating settlement. The potential for settlement damage was evaluated using both conventional analysis and finite element analysis

By E. D. Attanasi

Exploration for non-fuel minerals has declined since 1988 as recessionary pressures have slowed growth in the industrialized economies. By most accounts, however, 1990 expenditures were still significantly greater than the low levels experienced in the mid-1980s. The Persian Gulf crisis introduced instability in energy prices and greater uncertainty into an already cloudy economic picture. As 1990 unfolded, the US savings and loan problems spread to the commercial banking system, leading to the failure of several major US commercial banks. The Japanese stock market also suffered significant losses as Japan's Central Bank raised interest rates. The Soviet Union experienced shortages of food and other basic items. Its government faces resistance to changes leading to a market economy. Individual Soviet republics also are seeking more control of their own destiny. The cost of German reunification, in terms of the capital required to bring the east's infrastructure and industrial base to western standards, also appears to have been underestimated.

Jan 1, 1991

By B. Cavender

Mining managers trying to rapidly reduce production costs tend to implement a traditional set of topdown managerial practices: reductions in production volume, employee layoffs, renegotiation of supplier contracts, cancellation of employee training, restrictions on travel, reductions in office supplies, and so forth. While these practices do reduce costs, the benefits are often limited in both magnitude and duration, and the workforce is usually left demoralized. Successful cost-cutters take a different approach. They make the continuous reduction of costs a priority for all members of the organization, whether managers or workers. The culture of these firms emphasizes the commitment, voluntarily given, of individuals and work groups to this goal. Cost-cutting practices often reject all of the traditional methods mentioned above, but are far more numerous, innovative and successful. This culture of cost reduction is the result of a set of leadership competencies that establish direction for the organization, align the organization's various constituencies with this direction, and motivate and inspire the organization. Cost reduction then becomes a routine task rather than a heroic achievement.

Jan 1, 2002

By Natarajan K. A.

During sulphide ore grinding, electrochemical interactions between grinding medium and the minerals play a significant role in bringing out enhanced ball wear on the one hand and alter the surface property of the ground minerals on the other. The role of the flotation reagents added simultaneously during grinding with respect to ball wear as well as flotation is yet to be established. Electrochemical measurements such as rest potential, combination potential and galvanic current between sulphide mineral and ball material couples have been carried out in the presence and absence of flotation reagents to understand the nature of electrochemical interactions between ball material and sulphide mineral. Electrochemical mechanisms and models have been proposed to explain the role played by the flotation reagents during different binary, ternary and quaternary interactions with respect to ball wear during grinding.

Jan 1, 1992

By P. D. Pack, E. H. Skinner

During design of a 550-foot rectangular shaft in alluvium, lateral support within the excavation was an anticipated construction problem. Actual experience showed that the nearly 9 x 14 foot excavation required no lateral support. A strain measurement program con- current with construction and for a 9-month period following completion of the shaft detected only minor strains. Shaft design included consideration of available geological information. Site exploration included a 754-foot drill hole, cored at selected intervals, and a suite of geophysical well logs. Generalized physical properties of the alluvium were developed from laboratory core testing. An elasto-plastic, finite element computer program (DAHLKE) developed by the Spokane Mining Research Center U.S. Bureau of Mines, has been recently used to analyze the behavior of the alluvium around the shaft. Analysis showed that yielding first develops in the shaft corners and progressively expands into the wall zones around the shaft as loading increases. Gradual growth of a plastic zone progressed outward from the excavation boundary at increasing loads but had limited extent and was surrounded at all stress levels by an infinite elastic zone. This design review, aided by computer analysis, confirmed that the shaft would have been considered theoretically stable as designed.

Jan 1, 1977

By William R. Groseclose, Cecil E. Tackett

Since 1965 when the first mole was used on Bureau work, the Bureau of Reclamation has completed 17 tunnels of over 5,000 feet in length. The longest was 12.8 miles. Total length of the 17 tunnels was 376,207 feet, or over 71 miles. The finished diameter varied from 7 feet 0 inch to 18 feet 0 inch with 82 percent (58 miles) being less than 12 feet 0 inch in diameter when lined. All of these tunnels except one are gravity flow, water conveyance tunnels with relatively flat gradient. One is a low-head pressure tunnel. All were constructed by contracts resulting from fixed-price bids. Starting in 1964 the Bureau of Reclamation initiated the practice of giving several options in the specifications on methods of tunnel excavation. Since that time, construction work has been completed on 17 tunnels. Of this number, 11 were mole excavated and 6 were excavated by conventional drill and blast methods. In general, there has been 2 feet of mole excavation for every 1 foot of drill and blast. Cost comparisons are based on only 13 tunnels because the Bureau has 4 recently completed tunnels that have pending claims; therefore, final cost data are not available. Some definite trends show from the data available; however, the number of completed tunnels in some categories is so small the results cannot really be considered a trend. As more data become available, the indications will become more reliable. The information is presented to indicate general trends and comparisons and cannot be meaningfully used for a one-on-one comparison because of individual tunnel differences not considered.

Jan 1, 1974

By Neil Hillhouse

The Porgera gold district, like many other large gold deposits, has a long history of awareness, but only in the last five years has a geologic understanding of the district permitted the discovery of economically attractive gold reserves. The following sequence of events highlights the various significant steps in the evolution of the discovery process. The history of the district goes back about 50 years, and for several decades it was known only for its placer gold. Gradually, as gold became a more interesting metal, more and more attention was centered on the district. The sequence of events does not overstate the problems caused by isolation and climate, but the reader can imagine the difficulties inherent in such an area.

Jan 1, 1990

By Frank F. Aplan, Edward C. Jr. Dowling, Richard R. Klimpel

Thirteen kinetic models that mathematically describe the flotation process have been statistically evaluated for the flotation of copper, lead and zinc ores. Comparisons have been made for a variety of circuits involving roughing, cleaning, scavenging and regrind followed by cleaning. Variations in collectors, frothers, depressants and activators have been considered. Based on the statistical criteria used for the evaluation, and the reagent, circuit and ore variations studied, the most reliable flotation models have been identified and subsequently used to characterize the metallurgical results.

Jan 1, 1986

By Yunsheng Yao, P. Golledge, A. D. S. Gillies

In order to investigate the explosibility of sulphide mineral dusts, sulphide ore samples were collected from five underground metalliferous mines in Australia. The mineralogical and chemical composition of the dust samples was analysed by X-Ray Powder Diffraction and Atomic Absorption techniques. Simulated post detonation fumes were produced and used in dust explosibility tests to examine the influence of the fumes on sulphide dust ex- plosions. These tests were conducted in a 20 Litre Siwek Explosion Chamber with measurement and control system that is regarded as a standard testing system worldwide for dust explosion studies. The dust mineralogical composition and dust explosibility tests indicated that the content of sulphur can not accurately predict the explosibity of the sulphide dust. The percentage content of pyrite in the sulphide dust can be a relatively reliable diagnostic criterion in evaluating the risk of sulphide dust explosions in the mining of a massive sulphide orebody. The hybrid explosion tests demonstrated that the post detonation fumes from ANFO not only decrease the lower explosion limit of the sulphide dusts, but also increase the severity of the dust explosions. The explosion pressure reaches its peak value when the fumes content in the explosion chamber is about 20 per cent by volume

Jan 1, 1997

By J. Smolensky, M. Paul

The Nordhalde is a waste rock pile resulting from uranium mining near Ronneburg, Germany. The pile contains over 27 million m3 of waste rock. Typical seepage water has a pH of 2.7 and a sulfate concentration of 10,000 mg/L. Geochemical investigations of the Nordhalde from 1993 to 1996 included drillholes, test pits, ABA and metals analyses, column tests, and a detailed review of the construction history of the pile. In 1996, eight drillholes were instrumented for monitoring oxygen and temperature. Monitoring continued for a fill year. Hourly temperature and pressure readings were taken by automated data recorder. Oxygen concentrations were measured three times per week, and periodic gas samples were obtained for complete analysis. The resulting data set is believed to be one of the most comprehensive of its kind. Effects noted elsewhere, such as thermal convection, are evident. However, unlike other data in the literature, the NordhaIde data shows a strong seasonal effect, with convection dominating oxygen transport only in the winter months. Analysis of the data allowed the amount of contaminants associated with ongoing and historical oxidation to be compared, and results were used to assess the potential effectiveness of proposed remediation measures.

Jan 1, 2000

By Elwyn King, Donald J. Dodds

"...Unfortunately, the research activities in soil mechanics had one undesirable psychological effect. They diverted the attention of many investigators and teachers from the manifold limitations imposed by nature on the application of mathematics to problems in earthwork engineering. As a consequence, more and more emphasis has been placed on refinements in sampling and testing and on those very few problems that can be solved with accuracy. Yet accurate solutions can be obtained only if the soil strata are practically homogeneous and continuous...." This statement about soil mechanics was made by Karl Terzaghi, thirty years ago and applies to a greater degree today to the infant science of rock mechanics. More uncontrolled variables are added to the already many existing in soil mechanics. Variables, such as Macro-discontinuity and in situ stress levels. In no other field of engineering are the problems as site oriented. Presently this site dependance demands the investigator or rock mechanics engineer to get his hands dirty rooting in the muck of a tunnel floor trying to properly install or readout test apparatus in a comprehensive site investigation. This paper discusses such a site investigation designed to determine the problems and solutions inherent in the driving of the Trans Koolau Tunnel. The paper will describe the various types of tests to be performed, how the results are to be used and the interrelation of the various tests themselves.

Jan 1, 1997

By F. F. Peng, S. S. Peng, V. Z. Sun

A detailed study of ponding phenomenon relative to surface subsidence due to longwall mining was conducted for various surface stream conditions. Based on field monitoring, the stream-ponding process and three forms of stream water are described. Also discussed are the criteria of stream ponding and the influences on the ponding process by two key factors: the angle of stream flow and the change in the stream-bed gradient. A numerical (mathematical) model, which combines trend surface technique that describe the topographical features in the vicinity of a stream and the modified influence function, which represents the profile of the surface subsidence trough (or basin), is constructed to predict the formation characteristics of stream ponding in terms of location, boundary and accumulated water volume of migratory and stationary ponds produced by the stream-ponding process. Three cases are analyzed using the model to predict the interaction of the underground operations and the environmental impact due to stream ponding. The feasibility of various mitigative measures are assessed.

Jan 1, 1997

By C. B. Rash, W. W. Fowler, Gill Montgomery

INTRODUCTION Fluorspar is the common term used for the mineral fluorite, which is naturally occurring calcium fluoride (CaF2). It is the principal source of fluorine, the most reactive of the chemical elements, from which a great variety of unique and strategically important chemicals are produced. Commercial deposits of fluorspar are widespread throughout the world, and its availability is essential to the industrial progress of all nations. GEOLOGY AND MINERALOGY In its pure form fluorspar, CaF2, contains 51.1% calcium and 48.9% fluorine, and has a sp gr of 3.18 and a hardness of 4. It is commonly a glassy mineral. colorless, white, or grayish. but may also be various shades of purple, pink, blue, green, yellow, or tan. It belongs to the cubic system mineralogically, and commonly crystallizes into cubic shapes in vugs and cavities, although most of it is massive, with interlocking crystals. Minable fluorspar deposits, in descending order of importance, occur as bedded limestone replacement deposits along fault zones; fissure-filling vein deposits; breccia filling in limestones, dolomites,

Jan 1, 1985

By Michael J. Hannan, Thomas F. Torries

The nature of industry structure is examined and the structure of the aluminum, copper, lead and zinc industries are described by the use of factor analysis. Capacity is defined and the relationship between industry structure and capacity utilization is examined. It is demonstrated that excess capacity is possible in industries with competitive or monopolistic characteristics, but the effects of the overcapacity are vastly different in the two cases. In a competitive industry, cycles of overcapacity with attendant fluctuating prices are expected. A change in industry structure from monopolistic to competitive characteristics over time causes profits and economic rents to be transferred from the producer to consumers of the mineral.

Jan 1, 1989

By Julián Ortiz C., Clayton V. Deutsch

Indicator simulation allows specification of different continuity of high and low values through the use of grade thresholds. The sequential implementation of indicator simulation has been widely used, but the problem of order relation deviations remains a significant drawback. A new procedure for "Hierarchical Indicator Simulation" is introduced that avoids order relations and offers greater flexibility than the conventional sequential approach. The new implementation simulates all locations at the largest threshold and then considers decreasing thresholds in turn. All nodes with grades that are above the previous threshold are excluded from the domain of the current threshold and therefore, they are not used as conditioning data. The probability of being above or below the threshold is calculated using simple indicator kriging using all conditioning data in the domain, thus the covariance structure is preserved. The theoretical framework of this new approach is fully developed. Practical implementation details are discussed. Application to a copper deposit shows the advantages and drawbacks of the method. Finally, the possibility of incorporating multiple-point statistics is discussed.

Jan 1, 2002

By Paul F. Richardson

Liquids containing suspended solids are encountered in most mineral processing applications. Solids levels cover a very wide range, from ppm levels in cooling water systems to slurries containing greater than 70% solids. When the aqueous phase is recycled or further processed, a solid/liquid separation process is used. Chemical additives used to carry out this process are called coagulants and flocculants. In other cases, one seeks to control or modify the properties of the suspension. Dispersants are chemicals used to aid in suspending solids in a liquid as well as to control the properties of the resulting suspension. Dispersants find a range of uses in mining and mineral processing such as scale control, filter aids, flotation aids, and slurry viscosity modification. Materials used as dispersants include inorganic salts, alkalies, organic surfactants, and polyelectrolytes. This paper discusses the use of dispersants in mineral processing, with an emphasis on control of slurry viscosity. The mechanism of dispersion and factors that affect the choice of dispersant will be discussed.

Jan 1, 1986

By Shail J. Butani

This paper analyzes the 1982 coal mine accident data collected by the Mine Safety and Health Administration (MSHA) for key equipment types, by mine type, and by geographic region. The differences in hazards associated with the various equipment types are studied both in absolute (i.e., total number of incidences) and relative (i.e., incidence rate or the number of incidences per 200,000 employee or exposure hours) terms. The paper compares and contrasts the total number of incidents as well as incidence rates classified by several types of severity measures such as lost workdays cases, mean number of lost workdays per lost workdays case, fatal cases, non- fatal cases without lost workdays, total number of cases, and total number of lost workdays This statistical analysis shows that significant differences in hazards exist not only due to equipment type but also due to mine type and geographic region.

Jan 1, 1986

The molecular form of aliphatic amines precipitates in alkaline solutions when the amine solubility limit is exceeded and forms a typical colloidal system. The zones of mines precipitation and micellization are defined and it is shown that the appearance of a colloidal system in a certain pH range is a unique feature that makes weak electrolyte type surfactants differ from strong electrolytes. The formation of iono-molecular complexes reported in the literature is shown to be a pre-precipitation phenomenon. The zeta potential - pH curves for minerals and bubbles in the presence of amines in the pH range where the amine forms a colloidal precipitate are entirely determined by the precipitate. The pH dependence of the flotation of certain minerals using amines is discussed in the light of these findings.

Jan 1, 1989

By H. Fayed

Two-phase (water and air) flow in a self-aspirated WEMCO flotation machine has been investigated using computational fluid dynamics (CFD). The geometric model is a replica of a 300 m3 cell. A 72-degree sector containing two blades of the ten-blade rotor has been modeled and periodic boundary conditions are applied in the circumferential direction. Simulation of a sector of the machine allows acceptable resolution of the mean flow field using 4x106 grid points. The flow is modeled by Euler-Euler approach, and transport equations are solved using a commercial software ANSYS-CFX5 [1]. Unsteady simulations have been performed. In a self-aspirated machine, airflow rate is not known a prior; it is an output from the CFD simulation. Uniform mean bubble diameter of 0.7 mm has been specified as an input for the simulation. Air flow rate and power consumption have been monitored with time, and results indicate a stable operation. Air volume fraction contours and velocity field in different regions of the machine are presented and discussed.

Feb 27, 2013

By John Brouwer

Through the use of good preventive maintenance procedures in which the work of both production and maintenance personnel is well-coordinated, production downtime can be drastically minimized, and costly repairs and interruptions in planned maintenance and production schedules can be eliminated. There had been some conflict in the past between production and maintenance people over the proper method of achieving maximum machine performance. The usual practice was to operate production equipment at maximum capacity for the longest possible time until breakdown occurred, and then make hurried repairs to get back into production. In most cases, these repairs involved unscheduled work and were thus performed inefficiently. Both production and maintenance have the same objective: to produce a quality product at maximum efficiency and at minimum cost. Preventive maintenance is a common tool available for both production and maintenance personnel to achieve this objective. Actually, one of the main objectives of preventive maintenance is to find any abnormal machine condition that may cause machine failure before a breakdown occurs. This makes it possible to plan and schedule maintenance work with the least amount of interruption and plan production volume with a higher rate of accuracy. Maintenance people prefer to perform this work on a scheduled basis and get away from the "crash" situation that accompanies breakdowns. They thereby increase the utilization of available manpower and machine time, prolong equipment life, and improve maintenance costs.

Jan 1, 1979