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By Emad Iskander

The seepage forces generated around pressurized water tunnels in rock are investigated using the analysis tools of geomechanics. The theoretical background of the two-phase material behavior is explained and the equations of motion and continuity are presented. Applications on two case studies typically occurring in practice deal with the required minimum rock cover for a pressurized tunnel and the separation between two tunnels carrying different heads. The rock mass behavior as described by the Mohr-Coulomb and Hoek-Brown material models is investigated by numerical analyses and the results are compared. The effect of key material parameters on the safety factors and the associated modes of failure is discussed.

Jan 1, 2008

By M. K. Mohanty

Over the years, screen bowl centrifuges have been widely used for dewatering fine coal in coal preparation plants in the United States and elsewhere. Its popularity is attributed to its relatively low cost, its high capacity of providing low moisture content product and its relative ease of operation and maintenance. It is generally recognized in the engineering and scientific communities that screen bowl centrifuges provide some degree of particle size separation while dewatering fine coal in a common application. However, the extent of differential partitioning of coarse and fine particles achievable by a screen bowl centrifuge has not been systematically studied in the past. The present investigation was aimed at conducting a parametric study using a statistically designed experimental program to better understand and optimize the size classification performance of a screen bowl centrifuge. A continuously operating screen bowl centrifuge having a bowl diameter of 0.5 m was used for this study at the Illinois Coal Development Park. Three key operating parameters, i.e., feed flow rate, feed solid content and pool depth, were varied to conduct a total of 17 experiments using a three-level factorial test matrix. Some of the best size separation performances achieved in this study may be described as having an imperfection value of 0.13 at an effective separation size (d50c) of 38 µm and an imperfection value of 0.27 at an effective separation size (d50c) of 2.8 µm. Due to an effective separation of ultrafine high ash materials, the ash content of the screen bowl feed was reduced from 22.3% to a minimum of 8.84% with a combustible recovery of 84.1% and an ash rejection of 71.6%. A higher combustible recovery of 92.1% was achieved at a product ash content of 12.5% with a d50c of 2.8 µm and imperfection of 0.27.

Jan 1, 2008

By Tom Ireland, Tony Rock

The proposed 1.83km long twin bore A3 Hindhead road tunnel planned for contruction in 2008 is being delivered under a Highways Agency Early Contractor Involvement (ECI) contract. The proposed construction methodology is progressive mechanical excavation of a horseshoe shaped tunnel with shotcrete installed close behind the face using robotic spraying equipment. The tunneling medium is a ‘soft rock’ sandstone for which there was little previous tunneling experience, requiring extensive geotechnical investigations and an innovative approach to lining design. A 240m long portal section though sandy material utilising a steel pipe umbrella is also required. This paper describes the development of the tunnel planning and design including the most recent developments in UK road tunnels, and the innovation included in the ‘permanent’ primary lining design.

Jan 1, 2007

By Bhaskar B. Thapa

The proposed Caldecott fourth bore will consist of a two lane highway tunnel along California State Route 24 near the City of Oakland. The proposed design and construction sequence for the 15-m-diameter tunnel are based on the New Austrian Tunneling Method (NATM). The initial support system incorporates combinations of shotcrete, rock dowels, lattice girders, spiles, and grouted steel pipe canopies. The final lining is cast-in-place reinforced concrete. A waterproofing membrane and drainage system are placed between the initial and final linings. State Route 24 is a lifeline route, required to be open to emergency vehicles within 72 hours after a major earthquake, defined as having a return period of 1,500 years and a peak ground acceleration of 1.2 g. Although the seismic design criteria are stringent, the design of the tunnel lining system is ultimately controlled by static ground loads in the weak rock along the alignment.

Jan 1, 2008

By Klaus Rieker

North of Antwerp central train station, two single-track tunnels for the high-speed train line between Brussels and Amsterdam were constructed. At the same time, the central train station was modified to a through station. Both 1.23 km tunnels are situated in the Antwerp sands and were constructed using a slurry shield machine. Due to the inner city location, the tunnels run over their entire length underneath structures, in some cases with only minimal clearance. The paper deals with these challenging situations. In addition, the tunnel boring machine, the tunnel lining and measures to limit settlements will be introduced.

Jan 1, 2007

By Arthur M. Langer

Since the promulgation of the first Federal Asbestos Standard by the Occupational Safety and Health Administration in 1972, other federal agencies have modified the standard to better carry on their own unique missions. The instruments used to identify and measure asbestos, the sampling protocol, and the criteria used to define asbestos, have been modified to some degree. The Mine Safety and Health Administration regulates and controls asbestos dust in the mining and mineral commodity industries. However, crushed stone and processed ores contain mineral fragments that are frequently difficult to distinguish from asbestos. Mineral nomenclature, instruments for particle analysis, and sampling strategy must be accommodated to some degree to make asbestos control workable and meaningful. Precedent in other agencies has made consideration of these changes possible. Newly identified amphibole asbestos minerals have further complicated the agency?s regulatory charge. Changes in its Asbestos Standard are now being considered. Crushed taconite ore in the Eastern Mesabi highlights many of these issues. ©2008 Published by Elsevier Inc. Keywords: Amosite; Grunerite asbestos; Crocidolite; Riebeckite asbestos; Tremolite asbestos; Actinolite asbestos; Winchite asbestos; Richterite asbestos; Arfvedsonite asbestos; Fluor-edenite asbestos; Asbestos defects; Cleavage fragment; Mineral habit; Mesabi amphiboles

Jan 1, 2008

Breaks in coal slurry impoundments can threaten the lives and health of area residents, destroy homes and businesses and contaminate water supplies. This dangerous potential looms over coalmining regions in West Virginia and throughout Appalachia. The Coal Impoundment Project was begun in June 2003 to provide an inventory and mapping of active and abandoned impoundments in West Virginia. The project also provides the public with specific information about the impoundments in their communities. It is dedicated to alerting residents of danger and evacuation plans, reducing risk to residents and finding alternatives to impoundments. Since its first year, more than 100 impoundment sites have been added to the project’s Website.

Jan 1, 2005

By Russell Barr

Strategic alignment throughout a mining organization is critical to effective strategic execution and good business performance. The alignment of strategic goals and objectives in the different operations and functions in a large global operation is a challenge facing executive management in light of legacy organizational structure and processes. An additional confounding factor in strategic alignment of acquisition and new project expansion is that mining projects and operations are frequently multi-cultural in terms of country origin as well as organizational culture. This brings together many cultures to accomplish the project or complete an acquisition (Financial Times, 2006). The mining industry presents numerous challenges to executives and mine management by the nature of the operation and organizational processes used in running it. For example, there seems to be an inherent conflict between the individual goals of the components that constitute a mineral processing operation (the mine, the mill, the smelter and the refinery), and lowest cost production of the final product. Managers of these component operations have specific objectives passed down from the corporate executives. Those site managers tend to be compensated based on throughput and perform to this main metric. This tendency to maximize throughput for an individual operation can contradict the general process flow of a best-fit solution to producing the final product at the lowest cost. In an effort to become more aligned, firms are increasingly using balanced scorecard derivatives at great cost and effort (whether internally or externally sourced) in an attempt to help with strategic alignment. Balanced score-cards have been effective in providing a good strategic scorecard to companies with some measure of strategic alignment. Many firms make this effort of using balanced scorecards. However, most firms are not strategically aligned or, at best, are sub-optimized, in terms of strategic alignment (Kaplan and Norton, 2006). The tendency in mining operations is to focus on operating individual components as optimally as possible and stretching existing assets to the best possible production rates. ?Making tons? is the common operational focus. Numerous factors underpin this focus and can affect the ability of the operation?s ability to align properly with the corporate strategy and strategic goals. Critical factors are legacy organizational structure, culture, processes and performance measurement systems. Changing anyone of these factors to affect better strategic alignment requires significant attention to managing change.

Jan 1, 2008

By E. Z. Manos

The Detroit salt mine is operated by the Detroit Salt Co. It is one of the oldest underground room-and-pillar mines in the United States still in production. Mining at the Detroit salt mine began in 1906 with the sinking of the No. 1 shaft. Mining continued through the years, becoming progressively more modern in its equipment and techniques, until it was closed in 1983. In 1997, after a period of care and maintenance, the newly formed Detroit Salt Co. decided to reopen the mine. Upon completion of an extensive rehabilitation program, salt production resumed in 1998. Production currently continues at a rate of 910kt/a (1 million stpy). To date, the Detroit salt mine has mined more than 45 Mt (50 million st).This mine is unique because it lies under a heavily urbanized area within metropolitan Detroit. The mine and its history make a good case study for the continuing coexistence between the mining industry and its environs.

Jan 1, 2003

Development of a permanent human base on the Moon for exploration requires a self sustaining system. This entails production and processing of limited amounts of raw material on the Moon. Any mining and construction activities on the Moon can only be performed by a robust excavation machine that can excavate a variety of material from loose surface regolith to consolidated (frozen) regolith with embedded rocks in the mixture. Meanwhile, limited amount of information on lunar regolith is available to develop and optimize a machine for given lunar ground conditions. Therefore, any excavator designed for use on the lunar surface should have the ability to adapt to a wide range of operating conditions. A prototype cutterhead for the lunar excavator was built and tested at the Kennametal facility in Latrobe PA A. This paper discusses the results of initial material characterization as well as full scale tests of a prototype cutterhead inrelevent material. A brief review of anticipated production rates under various assumed ground conditions will also be presented.

Jan 1, 2009

By Larissa Koroznikova, Steve Durkin, Patrick Bouwmeester, Michael Tuck

In currently used mining methods, blasting techniques often causes dilution of valuable ore and results in costly processing requirements. In the context of narrow vein mining of thin and highly concentrated orebodies there is a need of a mining method that can reduce dilution in order to remain economically viable. This research project explored the viability of a new mining technology, thermal fragmentation, in narrow vein mining. Thermal fragmentation technology uses a flame jet to produce extreme heat that spalls the surrounding rock to a strategically located drill hole, as an alternative to traditional blasting. This paper creates a net present value (NPV) model of a mining method using thermal fragmentation, as well as for an existing method used for narrow vein mining; comparisons and evaluations were made regarding the feasibility of the new technology. It was found that while overall costs for thermal fragmentation were relatively high, reductions in wages, haulage and processing costs, as well as increased productivity and ore recovery, meant that the new method would improve the financial performance of any operation. These results identify that there is an opportunity to introduce the thermal fragmentation technology to narrow vein mines within Australia, in order to lower costs and increase profit.

By Steve Kral

Improved metals and other commodity prices have caused the mining industry to open new mines, re-evaluate development opportunities at potential mines and increase production at existing ones. This sense of renewed optimism is being seen at operations and development projects around the world. Except in the United States. The regulatory structure there has not allowed the domestic industry to share much in mining’s resurgence. It can still take up to 10 years to permit a new mine. And, while Clinton-era regulations regarding mill sites have been put on hold, existing mines that wish to expand operations still face significant regulatory and environmental hurdles. But things may begin to improve in the United States.

Jan 1, 2005

By R. K. Simpson, C. S. Eldridge, M. H. Tyler, J. P. Hodgkison

The WMC Olympic Dam Operation in South Australia is an integrated site, involving brown fields exploration through to production of copper cathode, uranium oxide, gold and silver bullion. The Geology and Analytical Services (GAS) Department reflects this totality and, therefore, is perhaps a unique construct in the industry. It comprises Geology, the Metallurgical Laboratory and the Analytical Laboratory, offering a single point of contact in matters of metal discovery and tracking through mine design, production, beneficiation and final product certification. This structure promotes value adding by removing traditional barriers between groups that can deliver more, collectively, than as individual units. This approach to value adding by bringing disparate groups together is echoed in each of the three sections where enhancements in the traditional value adding activities have been delivered by multi-skilling and encouraging overlapping involvement.

Jan 1, 2002

By Y. Q. Zhang, S. S. Peng

Numerical modeling was used to design the pillars and bolting plan for a mine with weak roof and multi-seam stress condition. Previous mining experience, pillar/roof yielding and in-situ horizontal stress were considered in the models. By modeling the upper seam yielding and vertical stress transfer, a multi-seam influence zone was obtained. Appropriate pillar sizes were designed for conditions with and without upper seam stress influences. Roof support for the track and belt entries, using fully-grouted resin bolts and cable bolts, was proposed and implemented in the model. The bolting plan was evaluated under the weak roof condition.

Jan 1, 2004

By K. Saikiran, A. R. Nalla

Longwall management, regular shield maintenance, and evaluation of ground control problems can be performed using real-time shield monitoring program. Based on real-time shield pressure data, evaluation of intensity and interval of periodic weighting, estimation of time-dependent pressure increase and the effects of geologic anomalies can be obtained. In this study, full-face shield pressure data of over 457 m (1,500 feet) of face advancement is analyzed to evaluate shield response in the presence of surface lineaments, floor undulations, and multiple main roofs. Shield pressure increase due to web cutting is also correlated with setting pressure during periodic weighting and normal time. In addition, time-dependent pressure increase rate on Sundays and holidays is also correlated with time average pressure and the location of previous periodic weighting.

Jan 1, 2000

By Morteza Gharouni Nik

Flexible Dilatometer Test (FDT) is one of the in-situ test methods for determining the deformational characteristics of rock masses. In this study, several dilatometer tests have been conducted in different geotechnical phases of site investigations by means of two types of FDTs. The purpose of this paper is comparison of the performance of these two types of dilatometers and analysis of the differences in the results of the tests.

Jan 1, 2008

By Hamed Khodadadi, Hamid Ghadiri

In this study, a fuzzy logic self-tuning PID controller based on an improved disturbance observer is designed for control of the ball mill grinding circuit. The ball mill grinding circuit has vast applications in the mining, metallurgy, chemistry, pharmacy, and research laboratories; however, this system has some challenges. The grinding circuit is a multivariable system in which the high interaction between loops, the variation of the system parameters with time, and time delay are some of the problems that pose a challenge. Since the controller parameters are determined offline in classic PID control, these gains are unchangeable and cannot overcome the mentioned challenges in this system. Hence, a fuzzy logic self-tuning PID controller, which is a combination of fuzzy logic and a conventional PID controller, is proposed to control the grinding system, especially in the presence of model mismatch and disturbances. In addition, in order to solve the system challenges, a multivariable control approach based on an improved disturbance observer is proposed to suppress the effects of the disturbances. The most important feature of the algorithm proposed in this paper as the combination of fuzzy logic self-tuning PID and improved disturbance observer is its ability to eliminate system interaction, attenuate internal and external disturbances, and compensate the effect of system uncertainty on the performance of the ball mill grinding circuit. Simulation results in the cases of the set-point change in particle size and circulating load in the presence of model mismatch and external disturbances confirmed the controller performance compared to other controllers.

By Hamed Khodadadi, Hamid Ghadiri

In this study, a fuzzy logic self-tuning PID controller based on an improved disturbance observer is designed for control of the ball mill grinding circuit. The ball mill grinding circuit has vast applications in the mining, metallurgy, chemistry, pharmacy, and research laboratories; however, this system has some challenges. The grinding circuit is a multivariable system in which the high interaction between loops, the variation of the system parameters with time, and time delay are some of the problems that pose a challenge. Since the controller parameters are determined offline in classic PID control, these gains are unchangeable and cannot overcome the mentioned challenges in this system. Hence, a fuzzy logic self-tuning PID controller, which is a combination of fuzzy logic and a conventional PID controller, is proposed to control the grinding system, especially in the presence of model mismatch and disturbances. In addition, in order to solve the system challenges, a multivariable control approach based on an improved disturbance observer is proposed to suppress the effects of the disturbances. The most important feature of the algorithm proposed in this paper as the combination of fuzzy logic self-tuning PID and improved disturbance observer is its ability to eliminate system interaction, attenuate internal and external disturbances, and compensate the effect of system uncertainty on the performance of the ball mill grinding circuit. Simulation results in the cases of the set-point change in particle size and circulating load in the presence of model mismatch and external disturbances confirmed the controller performance compared to other controllers.

By John F. Gamble

Amphiboles are hydrated mineral silicates five of which occur in asbestiform habits as asbestos grunerite (amosite) asbestos, riebeckite (crocidolite) asbestos, anthophyllite asbestos, tremolite asbestos and actinolite asbestos] and non-asbestiform habits (grunerite, riebeckite, anthophyllite, tremolite and actinolite). The asbestiform varieties are characterized by long, thin fibers while non-asbestiform varieties such as cleavage fragments form short fibers with larger widths. The U.S. regulatory method for counting asbestos fibers (aspect ratio [>]3:1, length [>]5 µm) does not distinguish between asbestos and cleavage fragments. The method biases toward increased counts of non-asbestiform cleavage fragments compared to long, thin asbestos fibers. One consequence of this regulatory approach is that workers can be erroneously classified as exposed to concentrations of asbestos (asbestiform amphiboles) above the U.S. 0.1 f/mL exposure standard when in fact they are not exposed to asbestos at all but non-asbestiform amphibole cleavage fragments. Another consequence is that the known carcinogenic effects of asbestos may be falsely attributed to non-asbestiform amphibole cleavage fragments of the same mineral. The purpose of this review is to assess whether amphibole cleavage fragments pose the same risk of lung cancer and mesothelioma characteristic of amphibole asbestos fibers. We identified three groups of workers exposed to non-asbestiform amphiboles: two groups exposed to grunerite (Homestake gold miners and taconite miners) and one group exposed to industrial talc containing non-asbestiform tremolite and anthophyllite in St. Lawrence County, NY. In addition to assessing strength of association and exposure?response trends in the non-asbestiform amphibole cohorts, comparisons were also made with cohorts exposed to the asbestiform counterpart (positive control) and cohorts exposed to the mineral (e.g. talc) that does not contain amphiboles (negative controls). The cohorts exposed to non-asbestiform amphiboles had no excesses of lung cancer or mesothelioma. Similar results were observed in the negative control groups, in stark contrast to the excess risks of asbestos-related disease found in the asbestos cohorts. The only possible exception is the twofold increased risk of lung cancer where exposure was to industrial talc containing cleavage fragments of tremolite and anthophyllite. However, this risk is not considered attributable to the talc or amphibole cleavage fragments for several reasons. A similar increased risk of lung cancer was found in Vermont talc workers, studied in the same time period. Their exposure was to relatively pure talc. There was no relationship between lung cancer mortality and exposure measured as mg/m3 years and years worked. A case?control study reported that all the lung cancer cases were smokers (or former smokers) and attributed the excess to smoking. There were two mesothelioma cases among the NY State talc workers exposed to cleavage fragments of tremolite and anthophyllite, but talc is not a plausible cause because of too short latency and potential for previous asbestos exposure. The positive controls of tremolite asbestos and anthophyllite asbestos exposed workers showed excess risks of both lung cancer and mesothelioma and positive exposure? response trends. St. Lawrence, NY talc does not produce mesotheliomas in animals while amphibole asbestos does. In sum, the weight of evidence fully supports a conclusion that non-asbestiform amphiboles do not increase the risk of lung cancer or mesothelioma. ©2008 Published by Elsevier Inc. Keywords: Amphiboles; Cleavage fragments; Lung cancer; Mesothelioma; Asbestos; Non-asbestiform amphiboles; Grunerite; Talc

Jan 1, 2007

Colloidal interactions play a critical role in mineral processing, including grinding, physical separation (particularly flotation), dewatering, and tailings management. Despite great energy input in comminution to liberate valuables from gangues, heterocoagulation between valuables and gangues would prevent the separation of valuables from gangues. On the other hand, selective coagulation/flocculation to increase the size of desired fine particles could enhance physical separation and dewatering, while dispersion is needed for fine grinding. To control the state of colloidal dispersions by creating favorable conditions, it is of paramount importance to study colloidal interactions in a relevant system and understand underlying mechanisms. This review summarizes recent advances in developing the-state-of-the-art techniques and novel methods of measuring colloidal forces, including atomic force microscope, surface force apparatus, zeta potential distribution measurement, quartz crystal microbalance with dissipation, and our recently developed integrated dynamic force apparatus. The basic principle of each technique was introduced first, followed by a summary of critical information derived for the relevant mineral processing systems. Finally, the pros and cons of each technique were discussed to emphasize the use of complementary techniques that assist in solving fundamental problems in mineral processing.