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By R. Poulin, R. C. Pakalnis

Approximately 51 % of all ore production in Canadian underground metal mines is derived directly from open-stope operations. This method requires that large excavations remain open until the ore is extracted with a minimum acceptable level of dilution. A survey of underground mines in 1988 reported that a major factor in their closure was uncontrolled dilution. It has been reported that 40% of openstope operations were experiencing dilution in excess of 20%. This level of dilution has significant implications on the economic viability of a project, especially when one considers that a rate of return on a positive project is generally between 10% and 20%. This paper reports on the various definitions of dilution, on the methods of stope design that are presently used with the objective of reducing dilution and on a recently available survey technique that enables dilution to be quantified.

Jan 1, 1996

By S. Serata

Background Results of the above study in the August 1991 issue of Mining Engineering offer valuable lessons in the solution of cutter-roof problems. The original study plan was initiated by the discussion authors to solve the problems using the "stress control method" of mining (Serata 1976,1982; Serata, Carr and Martin, 1984; Serata and Gardner, 1986; Serata, Gardner and Preston, 1986; Serata, Gardner and Shrinivasan,1986; Serata and Kikuchi, 1986; Serata, Preston and Galagoda, 1987) However, the plan and the planner were changed to the arrangement reported in the paper. The change was considered reasonable at the time due to the mine engineers' uncertainties about the stress control method. Consequently, the basic principle of the study was shifted from the original stress control method to the method described in the paper, which will be called the "yield pillar method" for the purposes of this discussion. The paper convinces the reader that the yield pillar method fails to solve the cutter-roof problems. This doesn't mean that the stress control method also fails. Actually the contrary is true, as discussed below. Limitation of the yield pillar method The paper illustrates clearly how poorly the yield pillar method performs in solving the problem. The reason for this failure is the lack of the protective stress envelope needed to stabilize the cutter roof. Unfortunately, the protective envelope cannot be formed properly without utilizing the stress control method of mining. Changing the pillar size does not make much difference in the roof stability.

Jan 1, 1992

By K. J. Stratford

The selection of a suitable mathematical function for the modelling of the partition curve for dense medium cyclones is discussed. Five alternative functional forms (based on three basic functions) are compared using data obtained in the course of an extensive experimental study of a 610mm dense medium cyclone. It is shown that, for adequately sampled tests, any of the functions may be used, although a function based on the Weibull distribution is shown to be most suitable. Where data are poor, all functional forms exhibit disadvantages, notably in terms of a reduction in precision of parameter estimation. This problem can be exacerbated by the complex numerical techniques required to estimate the parameters of a particular function. A set of ideal requirements for a performance function are presented.

Jan 1, 1986

By Y. T. John Kwong

Modified after procedures for assessing acid-generating potential of coal spoils, most acid-base-accounting (ABA) analyses inadequately characterize highly varied metal deposits. Although mineralogy critically controls acid generation and metal leaching, acquisition of appropriate data and their interpretation are poorly developed. Metal loading rates are commonly determined by kinetic testing, which rarely duplicate actual field samples and conditions. Accurate predictions and reduced assessment costs can conceivably be achieved by (i) use of geochemical analyses to define surrogate indicators; (ii) intelligent acquisition and use of mineralogical data; and, (iii) compilation of geo-environmental ore-deposit models to validate inference based on detailed geology.

Jan 1, 2000

By D. D. Snyder, J. D. Bode, F. T. King

INTRODUCTION Only in recent years have the environmental hazards associated with mining and tunneling operations been fully acknowledged and determined remedial action undertaken. The nature of these excavation operations leads to a wide diversity of hazards spanning mechanical, electrical, chemical, environmental, and physiological. The most insidious of these are unquestionably the environmental ones which have the greatest long-term effect and are the most difficult to pinpoint and monitor. It is the atmospheric contaminants that lead to a significantly greater illness and mortality rate among miners. Dust is the most prevalent, hence most important of the atmospheric contaminants. Respirable particles lead to diseases characteristic of many mining operations: coal workers pneumoconiosis, asbestiosis, silicosis, talcosis, anthrocosis, etc. But toxic and suffocating gases can be equally insidious and the most innocuous pollutant, methane, leads to the most imminently disastrous results of all - explosion and fire. This means that truly effective monitoring of the environmental hazards in tunneling cannot be limited to a few simple standard check measurements. It must include the most precise measurements we can make for specific, documented hazards and even for factors, such as noise and heat stress, not immediately obvious as hazards. The Federal Metal and Nonmetallic Mine Safety Act and more recent Occupational Safety and Health Administration standards are clearly designed to match such effective monitoring. We must, therefore, consider not only presently available monitoring instruments and those currently under develop-

Jan 1, 1997

By F. F. Peng, D. C. Yang, G. Yanief, E. H. Cho

This study deals with carrier flotation of cerium dioxide, a surrogate of plutonium oxide, which is the major contaminant at the Nevada Test Site (NTS). The objective of this study was to determine the feasibility of using carrier flotation for remediation of the site. In this study, a - 200-mesh fraction of pure cerium dioxide was used. Oleic acid was used as the collector, while calcium carbonate was used as the carrier. Mechanical-cell tests were conducted to float the surrogate from a mixture containing uncontaminated NTS soil, both in the absence and presence of the carrier. It was found that the addition of the carrier drastically enhanced the flotation recovery of cerium dioxide. The flotation recovery of the surrogate increased from 34% to 65% by adding only 0.5% calcium carbonate (-150 mesh). The recovery further increased to 95% by adding 10% calcium carbonate. The flotation method utilizing a carrier of calcium carbonate seems to have a high potential for the remediation of the soil contaminated with radionuclides at the NTS.

Jan 1, 1998

The most important event affecting the United States coal industry in 1993 was the strike by the United Mine Workers of America (UMWA). This was a series of selective strikes, beginning with a strike against four Peabody Holding affiliates on Feb. 2, following unsuccessful contract negotiations between the UMWA and the Bituminous Coal Operators' Association (BCOA). Although that strike ended on March 3, the failure to reach a new contract agreement led to walkouts at several Midwestern mines on May 10. During the summer, the strike expanded to include mines of 13 companies in seven states including Ohio, Pennsylvania, Illinois, Indiana, Kentucky, Virginia and West Virginia. About 17,000 miners were idled during the strike. As the prospects for a settlement diminished, the Secretary of Labor appointed a federal mediator. The mediation resulted in a five-year contract. In addition to increases in wages and pensions, it was agreed that 60% of new job openings would be filled by laid off and active UMWA miners. In return, companies won the right to establish more flexible work rules and scheduling of miners. While some health care benefits were expanded, the agreement established a new health care system that was designed to reduce costs. Preliminary Energy Information Administration (EIA) data indicate that US coal production fell by 5% in 1993, to 859 Mt (947 million st) (Table 1). The strike was one of the primary causes of the decline in production. Another significant cause was a 27% decline in coal exports. Also, a very small displacement of domestic coal production resulted from a rise in coal imports.

Jan 1, 1994

Diamond wire rock cutting is the most widely used technology in carbonate stone quarrying owing to technical performance and block face quality. Interest is also growing for siliceous deposits. This paper deals with the problem of optimum wire utilization under restrictions regarding a set of variables and parameters. A computer program of general applicability has been set up with the aim of studying the most suitable combination of technologies and the effect on the technical and economic results of bench geometry, overall quarry yield, market -stone value, quarry size as well as the quantity, productivity and price of human and material resources and their organization in the elemental working cycle. Two quarrying problems are considered as significant instances a granite and a travertine quarry. The results are illustrated and discussed.

Jan 1, 1989

By Stephen Utter

One function of mining is to supply oil shale of the required grade and characteristics to surface retorts. The mining methods must he safe, efficient, and environmentally acceptable. Although the Bureau of Mines no longer conducts research on methods of mining fossil fuels, including oil shale, its many years of activity in that field resulted in a significant body of findings. This article summarizes some of these findings, with respect to oil shale mining. The large areal extent of Green River formation oil shales and the diversity of geologic, hydrologic, topographic, and other conditions, preclude the use of any one single mining and waste management technique. Instead, in most instances, methods and equipment will be chosen to meet site-specific conditions. Such methods include conventional surface mining (open-pit and strip), underground mining (room-and-pillar, sublevel stoping, caving) and in situ extraction (true in situ from surface drill holes and modified in situ from underground retorts containing rubblized oil shale). Combination or hybrid systems may prove suitable. Both surface and underground backfilling of spent shale waste may be practiced. Tremendous amounts of oil shale must be mined, processed, and the waste shale properly disposed of in order to meet projected industry production goals. For example, about 1.4 tons of oil shale averaging 117 L of shale oil per ton are required to produce one bbl of oil. A plant with a daily production of 8 dam' (50 000 bbl) of oil would thus require some 68 kt of raw shale daily. This is more than the average daily production from any underground mining operation.

Jan 1, 1981

By Charles E. Joachim

Current Army tunnel destruction criteria (1) are based on limited nuclear-explosive (NE) and high-explosive (HE) test data. The PILE DRIVER (2) and HARDHAT (3) events investigated tunnel and support system response where yields were relatively large and tunnel diameter small compared to typical underground openings and localized stress fields of low yield weapons. Some limited tunnel destruction information was obtained from underground events of the PLUMBBOB and HARDTACK II Series (4). These events used access drifts which were designed to be self closing at the weapon point. The limited NE data are augmented by HE results from the Underground Explosion Test (UET) Program, a series of model and prototype-scale experiments in granite and sandstone (5). Weapon standoff distances (charge c.g. to tunnel wall) were at or near the maximum for major damage. Limited tunnel destruction was produced by a series of hasty and deliberate tests (6) on abandoned railroad tunnels in basalt. Additional HE data were obtained from model tests at the Waterways Experiment Station (WES) (7) using 2.1 MJ (2 lb) TNT charges and tunnel diameters varying from 3 to 17 cm (1.2 to 6.6 in). Recent laboratory scale HE experiments (8) conducted at the WES under the ESSEX program investigated the effects of tunnel diameter, standoff distance, charge confinement, material strength and to a limited extent, tunnel spacing and liner strength variations on tunnel damage. This paper summarizes the analysis conducted to develop predictions for the effects of low-yield nuclear weapons against tunnels and underground openings in rock.

Jan 1, 1979

By Richard L. Daley

Today's subject of discussion, "OSHA AND ITS PROBLEMS", must be covered in the time allotted with a slight tongue in cheek approach, for if one is to believe that the "problems of OSHA" can be covered in a twenty minute review, he, himself, has one of three problems: 1. He has residual combat fatigue left over from World War II. 2. He is an egomaniac. 3. He is afflicted with both of the above. Clearly, the difference between divinity and humanity lies in their work. All human endeavor is plagued by errors and omissions, and unless one would be so facetious as to equate bureaucracy with godliness, our government-sponsored ventures seem to receive more than their share of missive missles with which to combat the ills of our society. Coming from an industry known for its undertaking of gargantuan projects, I feel capable of looking at things from the big picture perspective. No one would deny that the massive influx of government, both in the monetary and supportive personnel roles, has accomplished much. But only we, as tunnel constructors, have moved countless mountains of muck, placed endless yards of concrete and engaged the public on numerous fronts and in spite of all, at times have even made a profit! Profit! What a dirty word in our society today. It makes one shrink back from the filthy overtones dripping with the cloying scent of decay. Never shall we judge the success of our government programs with such a slimy yardstick as profit. No, for that which has been conceived in the bowers of Camelot, the measure must be more elevating and inspiring. Something to bring a proud bearing to our efforts! Nothing has helped to alleviate the suffering of man as much as medicine. The eradication of typhoid, polio, and

Jan 1, 1979

By M. R. Nelson

Continuing experience in the Black Hills, South Dakota, indicates the persistence of several natural contaminants in mine waste effluents under circumneutral pH conditions. Selenium and arsenic are the most problematic environmental contaminants observed in these effluents. The contaminants are present in ore and waste rock as naturally occurring trace elements, and under the physico chemical conditions of the mine waste repositories are mobilized by oxidation and desorption reactions into infiltrating water. Characteristics of the mine wastes, waste repository construction, and Black Hills climatic conditions, indicate these natural contaminants may persist well into the future causing long-term mine closure liabilities, a difficult challenge to both mine operators and regulators.

Jan 1, 2003

By Richard Crawshay, Duncan Hutchison

Continuous Mining Systems Limited have developed an efficient, high-capacity, in-line loading unit capable of handling shot rock in tunnel driveages at extraction rates up to 970 tonnes (1,000 tons) per hour. A smaller 408 tonnes (450 tons) per hour loader is also available These in-line loading units called "Osciloaders"® provide a continuous flow of material from the muck pile to an anciliary conveyance eliminating the cyclic or interrupted movement noramlly associated with gathering arm or bucket type loaders. The osillating lip fluidizes the material, reduces the penetration force required and facilitates and regulates the material flow onto the adjacent conveyor. The conveyor is wide and accommodates very large material with ease, transporting and elevating it to a height suitable for a waiting conveyance at the rear of the machine. The "Osciloader"® is currently being utilized for production mining by a major company in Sudbury, Ontario. Both truck and conveyor anciliary haulage are being utilized. The paper describes the development of the loader and how it may be applied in tunnelling applications.

Jan 1, 1987

By S. Chander

The fundamentals of flotation are reviewed with an objective to understand the limitations in predicting the performance of a sulfide mineral flotation system and in its scale-up from laboratory studies to plant practice. The difficulties can often be traced back to complex interactions between chemical and physical parameters and nonequilibrium effects. The physical and chemical changes that occur during the long sojourn of sulfide minerals that begins with mining, continues through crushing and grinding, and ends when they emerge from the flotation cell as a concentrate, are reviewed. The benefits of new techniques that have become available in recent years to identify and estimate the amount of surface species are discussed.

Jan 1, 1999

By Werner A. Ruemmele, Steven R. Wardwell

INTRODUCTION The first phase of the Los Angeles Metro Rail Project consists of 7.1 km (4.4 miles) of subway and stations running through downtown Los Angeles from Union Station to MacArthur Park. Shank-Ohbayashi has two of the tunnelling contracts on this initial phase: A-171 and A-146. Contract A-171, the Wilshire/Alvarado Line, involves tunnel construction beneath 7th Street from the 7th/Flower Station to the Wilshire/Alvarado Station. The project consists of the excavation and lining of 3000 m (9900 ft) of twin-bore, 6.7 m (22 ft) excavated diameter, 5.5 m (18 ft) finished diameter subway tunnels. Contract A-146, the 5th/Hill to 7th/Flower Tunnels, comprises 1220 m (4000 L.F.) of twin-bore tunnel identical in cross section to the tunnels in Contract A-171. The majority of the excavation on Contract A-171 is beneath city streets in a weak siltstone/claystone bedrock with cover varying between 10 m and 25 m (32 ft and 82 ft) to the street surface. Approaching the 7th/Flower Station some fine-grained alluvium is encountered. The tunnels on both contracts are excavated with an open face digger equipped shield. On Contract A-146 the tunnel alignment is a 305 m radius curve of approximately 550 m (1800 L.F.) length underneath several multi-storied buildings of various construction. Excavation is still ongoing on Contract A-146. The contractor's choice for initial tunnel support on both contracts is a system of precast concrete segments similar to what the contractor had used on 7 miles of tunnel in Phoenix, Arizona, for the Arizona Department of Highways.

Jan 1, 1989

By John L. Habberstad, Robert R. Thompson, George B. Wallace, Robert C. Bates

INTRODUCTION Rock bolts are one of the most common mine support systems in use today with approximately 90 to 95 million used annually in the nation's coal, metal and non-metal mines. By far the largest majority of these are steel bolts with mechanical expansion shell anchors. Many theories have been advanced to explain the ground control achieved through the use of rock bolts. Most of the theories are applicable to a specific set of circumstances, geology, geometry, rock properties and in-situ stresses. Examples are those which relate the beam building or strata-hanging theories of ground support used in the rectangular openings of a coal mine(l). In tunneling and most metal mining, either circular or horseshoe shaped openings are normally used. Here, bolts may be used to develop a radial stress around the opening, which adds stability to that opening, or merely pin blocks of rock back into more stable ground so that they cannot slip. In most cases, the bolts are torqued to a specified value to seat the anchor and to achieve the pre-load or tension that is desired. To be effective, however, this tension cannot be lost through bolt slippage or creep frequently caused by blasting, moisture attack or raveling of the rock surrounding the drill hole, etc. Furthermore, in soft rock or in oversized holes, sufficient anchorage cannot be achieved with the mechanical anchor, and in very brittle rock the concentration of forces produced by the expanding anchor might cause a crack to propagate from one drill hole to the next. Mechanically anchored bolts are also short lived in mines or tunnels having a corrosive seepage. The steel in these installations can fail

Jan 1, 1974

By K. P. Unrug, E. Thompson, S. Nandy

The method of coal pillar design involves primarily two aspects: the geometry of the pillar and the strength of the coal. However, the strength of the coal has to be emphasized with respect to the entire pillar dimension rather than isolated strength values of coal samples taken and measured from different locations. As of now, the presently applied pillar design systems do not specify clearly what the coal sample strength really represents. The intention of this paper is to introduce the concept of seam strength as opposed to the current practice of using coal strength as a prime design criteria in the formulation of pillar calculations. Seams are most often composed of multiple layers of coal, partings, and bone in various configurations, changing within the vertical section of the seam even in relatively close locations. The difference in strength between the weakest and strongest component of the coal seam could be as much as five times or more. An experimental approach based on multiple uniaxial compressive strength tests performed on coal samples from the Coalburg and Warfield seams from eastern Kentucky was undertaken. Analysis of the results led to the conclusion that for pillar dimension calculations, both the weighted mean of the seam strength and the strength of the weakest stratum should be considered, rather than the relatively vague aspect of coal strength. The design of pillar dimensions based on the aforemen¬tioned criteria should assure a more realistic design performance.

Jan 1, 1987

By Gregg R. Bierei

Arch of Illinois is a mining complex comprised of two surface and two underground mines located in Perry County, in southern Illinois. The company a division of Apogee Coal Co. of St. Louis, MO. Arch of Illinois' two surface mines, the Captain and Horse Creek Mines, use large stripping shovels and cross-pit bucketwheel excavators to remove overburden from three seams of coal, the Herrin No. 6, Harrisburg No. 5 and Danville No. 7. All are considered high sulfur reserves. The two underground operations are managed by Arch of Illinois. They are the Kathleen Mine and the newly constructed Conant Mine, which began production in 1991. Both underground mines are continuous miner operations. They mine the No. 6 coal, which is about 1.8 m to 2.1 m (6 to 7 ft) thick. All coal is currently transported by truck to a central preparation plant located at the Captain Mine. This preparation plant produces 27 kt/d (30,000 stpd) of clean coal. Production in 1992 reached 5.9 Mt (6.5 million st) of saleable coal. Of that, about 66% or 4 Mt (4.4 million st) are produced by the surface mines and the rest the by under ground operations. Change is in the wind for Arch of Illinois. In 1988, 100% of all production (6.2 Mt or 6.9 million st) came from surface operations. By 1995, only 38% of production is scheduled from surface mines. And by the year 2000, 100% of production will from underground mining methods. Dwindling low ratio reserves, compounded by increasing environmental and land acquisition costs, coupled with more efficient underground mining equipment, have started an evolutionary trend toward development of underground reserves. For Arch of Illinois to maintain profitability of remaining surface reserves and to compete effectively mining underground, it must improve efficiency, productivity and cost reductions. These efforts are essential for maximizing current surface reserves and to ensure a continued existence in the presence of clean air legislation and the softening of the high sulfur coal market.

Jan 1, 1993

By F. M. Doyle, P. E. Richardson, E. Peters

A number of studies have attempted to correlate the semiconducting properties of mineral sulfides with their chemical reactivity. Frequently such studies are conducted on polished or abraded electrodes. Defects produced by abrasion may mask the influence of the semiconducting properties of electrodes, e.g., by pinning the Fermi level at the surface or by reducing the lifetimes of photogenerated charge carriers. It is shown that pyrite and galena electrodes have photocurrents that are extremely sensitive to abrasion of the electrodes. On freshly fractured galena surfaces, the space charge layer is readily polarized. Wet-abrasion is shown to produce a relatively thick ptype layer on galena electrodes and this p-type layer has a pronounced effect on the photoresponse. On freshly fractured pyrite surfaces, the Fermi level at the surface is pinned by a surface state. Wet-polishing reduces the magnitude of the photocurrent by over an order of magnitude.

Jan 1, 1993

By J. N. Adamson

The Alcan Smelter project at Lynemouth on the Northumbrian coast draws cooling water for the power station through shafts and tunnels from the North Sea. The sea at this part of the coast is frequently very rough and even in calm weather the coastal currents are strong. The adjacent coal mine makes use of these currents to disperse colliery waste and discharges into the sea some thirty thousand tons each week. In consequence the sea bed is continuously shifting and the sea is black and turbid. Construction of sea shafts under these conditions presents difficulties as drilling from a floating vessel is hazardous and sea bed activity of divers is greatly hindered by the entire absence of visibility. After considering several alternatives a method of construction was agreed with the Consultants in which the drilling and also the lining of the shaft would be completed in sequence from an eight legged work barge (GEM 126). Each shaft would be drilled to full depth and a steel cylinder, with its ends closed temporarily, would be lowered into the hole and grouted into the formation to form a full-length permanent lining. The bell mouth for each shaft would be constructed in advance to form part of the cylindrical casing. On interception of the shaft by its appropriate tunnel the lower end of the cylindrical casing would be cut away and the internal walling of the shaft installed from below. After completion of construction the shafts and tunnels would be flooded and the bell mouth sealing covers removed by divers.

Jan 1, 1997