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By Behzad Khorshidi

"The ultimate objectives of the post-tensioned strands are to connect the precast segments into a ring and provide pre-stress in the tunnel circumference. The method involves inserting the strand through the preliminary embedded duct in the precast concrete segments and then tensioning the strand by jack and fastening it. The post-tensioned strand eliminates the necessity of bolt connections between the segments and may reduce the labor cost and increase speed of lining construction. Pre-stressing of the segmental lining reduces the steel reinforcement or fiber volume in precast segments and/or thickness of the precast segments which would result in reducing the manufacturing cost of them. Pre-stressing would reduce cracking and increase water tightness, and would provide smooth intrados due to eliminated bolt joints and pockets in the tunnel lining. Pre-stressing would increase resistance to internal pressures as well. Further, this system could work very well structurally in tunnels with squeezing rock or tunnels with high seismic loadings. INTRODUCTION OF THE METHODPost-tensioning is commonly used in the construction of bridges, large buildings, nuclear power stations, and water tanks but its utilization in tunnels is still in its infancy.The precast pre-stressed concrete segmental lining can be used for shield tunnels. It provides a reinforced lining ring by the following construction stages and as shown in Figure 1:1) Segments to be assembled by TBM to complete a full ring2) Steel strand to be inserted through embedded duct (sheath) within the segments3) The strand to be tensioned by Jack after anchorage of the other end4) The strand to be fastened after reaching required tension load5) The horizontal strands (if necessary) to be installed, tensioned and fastened6) The recesses and gap between strand and duct to be filled by groutingFurther, Figure 2 shows an unbonded post-tensioning strand model; Figure 3 shows an anchor sample (Xanchor); Figure 4 shows a duct (sheath) and anchor within reinforcement; Figure 5 depicts the posttensioning of a strand by jack; and Figure 6 is an image of the Midorigaoka Trunk line tunnel in Sagamihara, Japan which was constructed using this system."

Jan 1, 2016

By Mohammad Ranjbar Hamghavandi, Mohammad Ranjbar, Zahra Manafi, Mohammad Hassan Fazaelipoor, Mahin Schaffie

The present study introduces a new approach to understand the copper dissolution rate and to find an adapted mathematical statement for particle shrinkage rate in a batch bioleaching system. Four size classes of a chalcopyrite concentrate, namely [D1 : (−54 + 44)μm, D2 : (−44 + 38)μm, D3 : (−38 + 25)μm and D4 : (−25)μm], were used in the batch bioleaching tests by applying a mixed culture of moderately thermophilic microorganisms. The pulp density and temperature were 8 (%w/v) and 50 °C, respectively. Findings delineated that the bioleaching time can be divided into two specific time intervals: first, the surface reactions were the prevailing controlling step; second, the prevailing mechanism was diffusion through the product layer, whereas the overall rate of the process may be related to both through a Q factor using a mixed model. A mathematical model was developed based on particle size distribution (PSD) and a kinetic model. Experimental validation of the mixed model was accomplished by the representative sample with d80 = 54 microns. Results showed that the PSD of the specific sample was in good agreement with Rosin–Rammler function. Besides, the simulation result of the conversion fraction had the best conformity with the experimental data (with a maximum error of approximately 7%). This paper should be considered as an initial part of a larger, global model for chalcopyrite concentrate bioleaching.

By A. Pradakar, J. G. Groppo, J. W. Leonard

All coal transportation systems from the coal face to the final point of use would become more productive if additional tonnages, obtained through improvements to bulk density, could be placed in fixed volume containers such as scoops, shuttle cards, trucks, barges and ships, as well as conveyors. This paper reviews previously reported work where the treatment of coals with small amounts of mining chemicals (0.12 to 0.28 kg/t or 0.25 to 0.56 lbs/st) during lavoratory testing was show to increase loaded coal bulk density by about 15%. The latest bulk density enhancement findings to develop from ongoing research involving underlying chemical and physical theory together with the added use of simple mechanical excitation are discussed.

Jan 1, 1995

By Jacob Carr, Christopher C. Jobes, Chenming Zhou, LaTasha R. Swanson, Jennica Bellanca, Jingcheng Li

Magnetic proximity detection systems (PDSs) are used with continuous mining machines (CMMs) to protect miners from striking and pinning accidents. Generators are used in a PDS to create magnetic fields covering the space around a CMM. The PDS determines the proximity of a miner relative to the CMM based on the magnetic flux density detected by a miner-wearable component (MWC) and simultaneously alerts the miner and stops the motion of the CMM if the miner is within a proximity that creates a striking hazard. A stable magnetic field is essential to the accuracy of the proximity calculations performed by the PDS. This paper presents the results of a systematic study of the magnetic influence of two types of steel structures found near a CMM— the body of the CMM itself and the wire mesh used for roof and rib control. The results show that the steel of the CMM body can change the magnetic field distribution and also alter electrical parameters of a PDS by changing its generator current. The study also shows that, depending on the distance between the wire mesh and a generator, the magnetic field can also be altered.

By James J. Brady, James S. Lewis, Robert B. Gordon, Jimmy W. Honeycutt

INTRODUCTION Tunnel construction has always been an extremely high risk form of contracting primarily due to the inaccessability of information concerning the ground conditions to be encountered during excavation. We certainly make every effort to overcome this problem through borings, geological research, site visits, etc.; but at best owners, engineers and contractors alike are only able to interpolate a relatively small amount of factual data from isolated sections of the project into a forecast of ground conditions for the entire project. In essence this becomes an "educated guessing game" with risk to reward ratios (and subsequently the bid price) in direct relationship to the contractor's confidence in the quality of the guess. In many instances it is economically or physically infeasible to obtain information and of course the total picture is never known until the project is complete. This problem effects the contract format as well as price. The contractor's ability to handle unforseen problems on the project become extremely important as to the project's overall success. The following pages contain an actual case history of a project which affords an excellent example of the entire spectrum of situations resulting from tunnel construction in difficult ground conditions.

Jan 1, 1983

Interstate 70 running into the mountains west of Denver, CO is the main access to the state?s numerous ski areas and other tourist attractions. As such, the highway is a vital part of Colorado?s economy. Due to the mountainous terrain in which it winds, I-70 is limited to two lanes in either direction. And, during the past few decades, the volume of traffic has increased to the point where motorists encounter major delays, particularly on Friday evenings and Saturday mornings heading west from Denver, and then again on Sunday evenings heading east. In the past, those delays occurred mostly during the ski season. However, many of the mountain towns have been successful in turning their resorts into year-round vacation destinations. A good move economically, but the pressure added to I-70 has caused even greater traffic delays, sometimes to the point where some Front Range residents avoid trips to the mountains.

Jan 1, 2013

By M. T. Ityokumbul

The effect of reaction conditions on the desulphurization of oil sand coke residues has been studied. The variables investigated were temperature, reaction time, heat transfer resistance, and mode of caustic soda addition. The results obtained show that oil sand coke desulphurization increases with temperature, reaction time, and heat transfer rate. In an oxidative environment, coke combustion during molten caustic leaching (MCL) commences at temperatures above 500°C. The mode of caustic addition has no effect on coke desulphurization.

Jan 1, 1995

By Broderick E. Davis

Each year, about 45 Mt (50 million st) of flotation tailings are discarded in Florida phosphate operations. These tailings only contain about 4% of the phosphate in the ore. However, more than half of the phosphate in the tailings is concentrated in the +600 µm (+28 mesh) size fraction at grades of up to 20% P205. Many phosphate producers have attempted to solve this problem by floating the +425 µm (+35 mesh) flotation feed separately. However, phosphate recoveries in these circuits are typically only 60%. For seven sampled phosphate operations, the phosphate content of the +600 µm (+28 mesh) fatty acid tailings ranged from 15% to 25% P205. In every case, the +600 µm (+28 mesh) fatty acid tailings was higher in grade than the overall flotation feed. Attempts to efficiently recover this coarse phosphate have apparently been unsuccessful at these seven phosphate operations. Recovery of this coarse phosphate would provide an additional 900 kt to 2.5 Mt (I to 2.7 million st) of phosphate annually and add an additional year to the reserves of these important deposits. A typical central Florida phosphate matrix is composed of three different mixtures of minerals. The +1.18 mm (+ 16 mesh) portion is chiefly phosphate pebbles and is beneficiated by sizing. The -106 µm (-150 mesh) portion contains virtually all of the clay minerals and is discarded in the hydrocyclone overflow. The -l mm +106 µm (-16 +150 mesh) material is a mixture of quartz and phosphate minerals.

Jan 1, 1993

By Tetevi B. Wilson

Analysis of the distribution of ore-bodies in space can be useful generally in the estimation of mineral resources or the management of exploration. This study is di¬rected to analysis of the undiscovered potential of well known areas of mining district size, referred to as metallogenic units (MUs). The analysis employs an effort¬ adjusted and truncated probability model for number of occurrences within a subdivision (quadrat) of a MU and Monte Carlo sampling to generate an approximation to the probability distribution for number of occurrences and number of mines within an MU when it is totally explored. Exploration potential for Monitor, Bodie, Au¬rora and Camp Douglas MUs (Walker Lake quadrangle of Nevada and California) are estimated to be 9, 4, 7 and 4 mines, respectively.

Jan 1, 1992

By Michael J. Nicol

Hydrometallurgical processes involve the recovery of metals from ores, concentrates, calcines, mattes and scrap materials by a series of operations involving leaching or dissolution, separation, purification and reduction of metals in aqueous solutions. The underlying theoretical basis of many of these operations is electrochemical in nature and it is the purpose of this review to identify and illustrate, by way of examples from the author's experience and that of others, the central role of interfacial electrochemistry in the understanding, design and control of these operations.

Jan 1, 1993

By Gordon M. Pugh, David G. Rasmussen

INTRODUCTION Variations of cut-and-fill stoping are the most com¬monly used methods for mining narrow, nearly vertical veins in the United States. These methods offer the best results for maximum recovery with minimum dilution of ore from veins that are irregular along either the strike or dip. The vein is developed along the strike length in 61 to 122-m (200 to 400-ft) blocks or stopes and vertical lifts of 48 to 61 m (160 to 200 ft). The level development is either on the vein or parallel to the vein with crosscuts intersecting the vein at right angles. Chutes, manways, and haulageways are established in the center of the stopes at the lower level of the ore block. Mining then proceeds by blasting down horizon¬tal cuts of the vein in both directions from the chutes. As the blasting continues to the outer limits of the stope, the broken ore is slushed into chutes. When a complete horizontal cut has been made, the service raise, including chutes, is raised to a height of a few feet from the back and the stope is filled with either sand fill or waste rock. Then the mining cycle is re¬peated until the stope reaches the level above. LEVEL DEVELOPMENT PRACTICES FOROVERHAND CUT-AND-FILL STOPING The two basic methods used are: the development of the haulage drift within the vein, or development of the haulage drift paralleling the vein in the foot or hang¬ing wall with crosscuts intersecting the vein perpendicu¬larly at 61 to 122-m (200 to 400-ft) intervals. The il¬lustrated methods of development show some of the variations which can be used to develop a stope block. Development for cut-and-fill stoping does not require the more elaborate schemes outlined for shrinkage or sublevel long-hole stoping. Many factors must be considered before deciding on a particular development plan and usually the nature of the vein or host rock will dictate which specific method to use. If the vein is relatively straight, then develop¬ment on the vein is feasible. Excessive ground pressures will necessitate the leaving of a sill pillar (Fig. la) and highly fractured or "heavy" ground will require timber¬ing (Fig. 1b). Development on the vein has the advan¬tage of reducing capital outlay and waste handling prob¬lems since the mined rock has value. But removal of the sill pillar is costly and time-consuming. Also, where no sill pillar is left, excessive timbering and subsequent level repair is a drawback. Development in either the footwall or hanging wall is the more common procedure and offers greater flexi¬bility in overall development of consecutive stoping blocks by partially disassociating the level development from stoping (Fig. 2). Chutes, manways, and service compartments com¬prise the next stage of development and are established in a variety of ways. They provide access to the stope, ventilation ducts, and muck removal. Several different development systems are in common use and average costs for each have been developed. Raise borers are used to establish ventilation and ac¬cess from level to level. They are normally reamed with 1.5 or 1.8-m (5 or 6-ft) cutterhead and may either be left bald or lined with a 1.2-m (4-ft) diam corrugated liner plate, depending upon ground conditions. The use of an Alimak raise climber is another effec¬tive method of driving a raise from level to level. The size usually is 2 m (7 ft) square. This will accommodate square-set timber which is later installed. This method of raising is not common, although it is a valuable tech¬nique especially when level spacing is several hundred feet.

Jan 1, 1982

By J. Creamer

Pumping plays a major role across multiple process and facility applications in the mining world. Examples include: raw water supply, leach solutions, chemicals, dewatering, and mine drainage, and process water for metal recovery. Mining operations such as grinding, classifying, separating and concentrating minerals all have pumps at the heart of the operations Special purpose pumps such as dewatering, process water and slurry pumps are at the heart of many of these processes. Unfortunately the pumps themselves are often overlooked in terms of energy savings potential as they are often embedded into these sophisticated processes which are the ultimate operational focus.

Feb 23, 2014

By B. A. Kuyper

The Cove gold-silver deposit is located 50 km southwest of Battle Mountain, Nevada and 1.5 km northeast of the McCoy Mine. Total proven and probable reserves are 48.7 Mt (53.7 Mst) with an average grade of 1.85 g/t (0.054 oz/st) Au and 87.1 g/t (2.54 oz/st) Ag. Mineralization is hosted by Triassic carbonate and siliciclastic rocks in two separate orebodies. Oxide ore consists of disseminated gold and silver in clay-altered, manganese-flooded limestone. Sulfide ore is dominated by pyrite-sphalerite-galena veins in siliciclastic rocks and sandy dolomite. Gold and silver occur in the native state, associated with the base metal sulfides. Mineralization is interpreted to be the distal expression of a porphyry system. The McCoy gold (copper) deposit is interpreted to be the proximal expression of the same system.

Jan 1, 1991

By P. G. Irwin

Natural resins, those derived from coal and those mined in the Uintah basin, face challenges from synthetic resins that are derived from petroleum sources and rosin or wood sources. In the past, fossil resins from coal were produced by various companies, the last one being Hercules, Inc., which sold BLACKHAWK resin until a fire destroyed the plant in the mid 1970's. Approximately four to fjve million pounds of BLACKHAWK were produced and sold mostly to the printing ink industry. Uintaite, more commonly known as Gilsonite® resin, was widely used by various industries, notably in printing inks, coatings, stains, adhesives, foundry, asphalt paving, and oil well drilling muds. Gilsonite has lost market share over the last thirty years to various synthetic resins particularly hydrocarbon resins that are derived from petroleum sources.

Jan 1, 1990

By J. Ainsworth, W. Trudel, L. Schutz, C. L. Bolin

Newmont mine geologists have added substantial economic value developing over 1,150 tonnes into quality surface and underground gold reserves since 1986. However, the recent 5-year gold price slump from $387 to $262 per ounce has shifted mine geologists focus to optimizing open pit profitability and developing high-grade, high cash flow and low capital development underground reserves. More than $65 million projected revenue has been added to the Gold Quarry south layback following multi-departmental model reconciliation investigations. Kriged mine polygon construction, controlled blast heave and high-quality geologic advice in selective mining will have multi-million dollar beneficial impacts.

Jan 1, 2002

By T. S. Golosinski, J. Wolski

Procedures are presented for determining the hourly production rate, mechanical and physical availability, utilization, use of availability, and global performance factors for the bucket wheel excavator (BWE) itself, as well as for the system composed for the BWE, conveyors, and stacker. An example demonstrates the flow of calculations. Using available data from mines that use BWE technology, the ranges of values of the BWE performance factors are presented in tabular form. They can be used as a guide during mine planning as well as to evaluate existing systems.

Jan 1, 1987

By Błażej Doroszuk, Robert Król

Mill drums are essential equipment in various industries for the comminution of materials. To optimize their design and operation for efficient and cost-effective processing, it is necessary to understand the behavior of the mill drum under various operating conditions. This study investigates the behavior of a mill drum using a combination of experimental and numerical methods. The factors that can influence the behavior of the mill drum, such as the size and shape of the mill, grinding media, rotational speed, filling level, and material properties, are discussed. Experimental methods can be limited in obtaining measurements of internal processes, so numerical methods such as the Discrete Element Method (DEM) are also used to simulate the behavior of the mill drum. In this study, the experimental measurements of the motion of the grinding media are obtained using computer vision methods, and the numerical simulations are calibrated using the experimental results. A designed experiment approach is used to evaluate the performance of the mill drum under various operating conditions. The results of this study can be useful for the design and optimization of mill drums to achieve better performance and energy efficiency.

Jun 25, 2023

By N. P. Titkov

This paper presents the results of laboratory and pilot plant investigations for the development of efficient methods of beneficiating hematite ores from the Krivoi Rog, Kursk Magnetic Anomoly, Olenogorsk, and other localities. The tests included gravity, magnetic (in a high intensity field), flota¬tion, and magnetizing roasting methods. It was possible to develop efficient beneficiation methods depending on the mineral composition of the ore and degree of dissemination of ore and gangue minerals. The paper shows the relationship between the iron silicate and quartz content of the ore and the technologic indices of the various beneficiation methods. Some of the conclusions based on these investigations and the technical and economic computations related to the cost of one ton of pig iron produced from concentrates obtained by the various beneficiation methods are: 1. If the hematite ore is not disseminated uniformly, it is expedient to use a combined gravity and flotation process. Ore particles up to 50 am. in size are beneficiated by gravity (heavy suspension, jigging, and others) and yield a lump concentrate. The middlings from this process are recrushed and floated; 2. Finely disseminated hematite ores, containing small quantities (less than 5 percent) of iron silicates, are most effectively beneficiated by flotation. Anionic (sulphate soap, tall oil emulsion with various foam depressors) as well as cationic collectors may be used. Depending on the mineral and chemical composition of the ore, it is possible to obtain concentrates containing up to 65 percent iron with an extraction up to 94 percent; 3. Finely disseminated, mixed hematite-magnetite ores may be beneficiated by flotation or a magnetic separation-flotation process; 4. Finely disseminated hematite ores, containing large quantities of iron silicates and earthy hematite ores are most efficiently beneficiated by the magnetizing roasting method. This method will yield concentrates containing up to 68 percent iron with extractions up to 90 percent. Although beneficiation by the magnetizing roasting process is costly, it will nonetheless, when employed on this type of ore, yield the least expensive pig iron.

Jan 1, 1960

By Song Xiaotian

Studies have been carried out to optimize the VCR's mining sys- tem on the basis of synthetic analysis at Fankou Pb-Zn mine in Southern China. The synthetic e- valuation method is proposed for selection of mining alternatives and stope dimension optimization techniques. Theoretic calculation and computer optimization of the fragmentation of rock blasted by multispherical explosive charges are discussed. The mathematical and optimal fragmentation models are built. The optimum model is built for the main mining operations such as drilling, blasting and haulage. Lt can be used to evaluate VCR?s mining projects, select mining parameters and provide design fundations. From the point of view of system research on the geomechanical process, stoping technological process and benefit, the complex method of optimization is proposed for VCR's mining. Using computer simulation, based on this model, the optimal parameters are established and analysed. An effective approach is provided for research on the mining method optimization and getting better economical benefits from the application and improvement of VCR's method.

Jan 1, 1986

By Y. Xi, T. M. Yegulalp

An availability approach for determining the capacity of a major Bucket Wheel Excavator (BWE) system to be used in the Yuabaoshan Surface Coal Mine in China is presented in this paper. Based on previous studies on other BWE systems for delay times due to internal and external causes and a four-level maintenance and repair schedule, a model was developed, taking into account all random failures, to present a fast and simple solution to this highly complex problem. A procedure employing the Markov renewal theory for determination of the distribution of random failure times and failure rate of the whole system, as well as some other factors useful for calculation of the overall system capacity, are discussed.

Jan 1, 1994