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By D. S. Choi

Underground production of coal by longwall methods has increased significantly in the last few years and will very likely continue to: increase. There are several reasons for this. First, as mining moves into seams having greater overburden, roof exposure must be reduced since support will become' increasingly expensive. Secondly, the growing demand for coal has forced the coal industry to seek alternative, more productive, coal mining methods. In addition, the longwall method greatly simplifies the underground ventilation network. This paper addresses itself to the design of longwall development headings, particularly to those of the United States where multiple development headings are required by law. The most burdensome problem encountered in many longwall mining installations is deterioration of the tailgate due to the combined effect from, the active longwall gob and the old gob made by mining the previous panel.1 Portions of the tailgate entry are sometimes closed to such a degree that extensive repair work is necessary to keep the entry in usable condition. The purpose of this paper is to present the result of a study in progress which combines field measurements with numerical model analysis to reduce the cost of maintaining tailgate entries in longwall mining systems.

Jan 1, 1975

By Richard E. Ray

INTRODUCTION Main mine fan installations at underground coal mines must be designed to comply with the requirements outlined in 30 CFR (Code of Federal Regulations) Part 75. However, very little emphasis is typically placed on the aerodynamic optimization of shaft collar designs, ductwork configurations, and the selection of a fan isolation, or "closing door," system. Field testing has shown that poorly designed systems may produce large pressure losses between the shaft and fan inlet, as well as air turbulence problems which adversely impact fan efficiency and sometimes fan structural integrity. This paper analyzes each component of a surface exhaust fan system for an underground coal mine: • The shaft collar arrangement, • The 45 or 90-degree turning duct that isolates the fan motor from the return airstream, • Alternative ductwork arrangements for parallel fan installations, • The self-closing doors or dampers that are required for multiple fans, and • Horizontal and vertical evas6 arrangements on the discharge side of the fan. While discussion is limited to axial fan installations at shaft mines, most of the recommendations would also apply to centrifugal fan installations and to main mine fans for drift mines. FEDERAL REGULATIONS The mandatory safety standards for underground coal mines that apply to the installation of main mine fans are listed in 30 CFR Part 75.310. Stipulations which impact the design of the fan sys- tem arrangement are contained in paragraphs (a)(l), (a)(5), (a)(6),(d), and (1) of 75.31 0: • Each main mine fan shall be installed on the surface in an incombustible housing; • Each main mine fan shall be protected by weak walls or explosion doors in direct line with possible explosive forces; • Explosion doors or weak walls shall have a cross-sectional area at least equal to the area of the return air shaft or drift opening through which the pressure from an underground explosion would be relieved; • Each main mine fan shall be offset by at least 4.57 m (15 feet) from the nearest side of the mine or shaft opening; • Automatic closing doors shall be provided to prevent possible air reversals through the fans in mines ventilated by multiple main mine fans. The installation of main mine fans underground is prohibited by 30 CFR Part 75.310, (a)(l). Providing explosion doors or weak walls in line with a possible underground explosion and offsetting the fan 4.57 m (1 5 feet) from the edge of the shaft preclude the installation of the fan directly over the shaft. In addition, 30 CFR Part 75.507-1 specifies that all electrical equipment used in return air courses be permissible, which requires locating the fan motor outside of the airstream exhausted through the fan. To comply with the Part 75.310 regulations, explosion doors are typically located directly over the shaft as part of the shaft cover or 'bonnet." A sufficiently long section of ductwork placed between the shaft enclosure and fan, equipped with a 45 or 90- degree turn, enables the fan to be offset at least 4.57 m (1 5 feet) from the shaft and the motor to be isolated from the airstream. The need for the turn in the ductwork can be eliminated by driving the fan from the discharge side, instead of from the inlet side, and providing for a 90-degree bend in the evas6. For multiple main mine fan systems, self-closing doors can be located on the inlet or discharge side of the fan. FAN SYSTEM COMPONENTS A poorly designed exhaust fan arrangement will produce turbulent conditions at the fan inlet and significant pressure losses between the shaft and fan. Field tests have shown that pressure losses through inlet ductwork at some installations may constitute as much as 30 percent of the total mine head. Unfavorable flow conditions may cause a change in the operating point on the fan performance curve, resulting in reduced fan efficiency and pres- sure generation capability. In some instances, poor airflow distribution through the fan may create mechanical stresses that lead to fan blade or fan housing fatigue failures. The objective in designing an air duct arrangement for a fan system is to provide a low cost duct that will move the air from the shaft to the fan in a uniform air distribution and with minimum energy requirements. The optimum solution is a compromise between technical and economic factors. Aerodynamic design considerations for the shaft collar and cover, fan inlet ductwork for both single and parallel fans, self-closing doors, and evas6 are discussed in the sections below. Shaft Collar/Cover To prevent excessive turbulence and non-uniform air distribution through the fan, a smooth transition for the change in direction of airflow at the top of the shaft must be provided. However, the concrete lining of the shaft is abruptly terminated at the surface at many coal mine installations (see Figure I), creating a sharp 90-degree bend. The airflow exiting the shaft becomes heavily concentrated in the upper portion of the horizontal fan in-

Jan 1, 1997

By Jan Jekielek

Increasing capacity of bulk material handling systems creates difficult problems for accurate in-line material weight measurements. At the same time increasing system complexity and growing user demands call for more measurements. Precision in-line weight measurements for bulk materials are usually accomplished by application of conveyor belt scales. Belt scale accuracies listed by scale vendors are applicable for ideal situations with suitable conveyor design, belt scale location and calibration means. This paper attempts to provide designers and users with simple means to evaluate belt scale accuracy for practical scale installations. Based on known mathematical models simplified formulas for measurement errors are derived and discussed. These formulas allow for simple determination of achievable accuracy for alternative scale installations on the conveyor, conveyor designs, etc.

Jan 1, 1979

By William A. Rhoades

INTRODUCTION Ever since miners were faced with the task of moving ore, some form of scraper has been in use. At first, men and beasts of burden supplied the power to move the scraper, and later, machines were developed for this purpose. In the early 1900s, a few mining properties used small pneumatic single-drum winches to pull loaded scrapers to a raise or ore pocket, and the empty scraper then was dragged back to the muck pile by a miner, as shown in Fig. 1. Just prior to 1920, an improvement was introduced, using two single-drum hoists. As illustrated by Fig. 2, the second hoist was used to return the empty scraper to the muck pile. However, this arrangement still re¬quired two men, one operating each hoist. The next developmental step was to eliminate the second man by locating the hoists side-by-side and using one man to control both hoists. As illustrated by Fig. 3, this involved the use of a tail rope over a sheave to pull the scraper back. The greatest progress in development and the great¬est increase in the use of slusher haulers occurred between 1920 and 1930. In 1921, the Sullivan Machinery Co. designed and built the first two-drum scraper oper¬ating on the principle illustrated by Fig. 4. It was powered by a 4.5-kW (6-hp) Turbinair(r) motor and would pull a 450-kg (1000-1b) load at 0.61 m/s (120 fpm). In 1922, this unit was shipped to the Verona Mining Co. of Caspian, MI, and it experienced immediate success in the Lake Superior iron ore district. Since the two-drum slusher was much less expensive and more efficient than hand mucking, the Lake Superior mines were saved from financial disaster when iron-ore prices fell 25% between 1923 and 1925. Immediately there¬after, a demand developed for slushers that would oper¬ate with electric power, which was considerably cheaper than compressed-air power. In 1923, the Sullivan Machinery Co. responded with the first electric-powered double-drum hoist. During subsequent years, design improvements in¬cluded separate tail-drum gearing to increase the tail¬drum speed, as welt as a number of safety features such as rope guides. One result of these improvements and their utilization by the Michigan iron mines was an in¬crease of 100% in the tons of ore per miner per day in those mines between 1924 and 1929. Since the two-drum slusher was capable only of straight-line mucking, it was not a practical machine for use in open stopes. In 1929, the Sullivan Machinery Co. introduced the first three-drum slusher. As illustrated by Fig. 5, two tail drums and one hauling drum were provided. A tail sheave could be placed at each side of the stope, and the ore then could be loaded and hauled to a central point from the entire width of the stope. During the 1930s, progressively larger slushers were demanded. By 1940, two- and three-drum units were available with motor power as high as 45 kW (60 hp), and slusher power continued to increase after 1940. Be¬tween 1951 and 1952, Joy Manufacturing Co. designed a 112-kW (150-hp) two-drum Blusher for the Climax Molydenum Co. Although there has been no demand for a slusher more powerful than this, 150- to 225-kW (200- to 300-hp) slushers are quite feasible at the pres¬ent time. During the last 30 years, many slusher improvements have been made to the operating life, operational safety, and ease of operation and maintenance. Increased tail-drum speeds have decreased overall scraping times. Rope guards, totally enclosed drums, and operator shields have reduced the hazards of injury due to wire¬rope breakage. Improvements in lubrication have made the slushers relatively maintenance-free, with long operating lives. The introduction of spring-actuated drag brakes prevented uncontrolled unreeling of dis¬engaged drums, allowing the development of practical remote-control slusher operation. Remote control now is available in a choice of all-air, all-electric, or air¬electric slushers. APPLICATIONS Quite simply, slushers are used to load and transport material (ore), generally over a short distance of from

Jan 1, 1982

By Parris A. Lyew-Ayee

This paper is the first preliminary report on the bauxites and terra rossas of the Caribbean. It concentrates on the islands of the Greater Antilles, and for reference purposes the Yucatan Penin- sula is included. At this point, observations made in Jamaica, Haiti, and the Dominican Republic are compared with reported information on Puerto Rico, the Bahamas, Cuba, the Cayman Islands, and the Yucatan Peninsula with regard to occurrence, as well as physical, chemical, and mineralogical composition. From this, an attempt is made at classifying the types of bauxites in the Caribbean, indicating the best reserves estimates, and the process ability of these bauxites. Some suggestions are also provided to fuel the controversy over the likely source material(s) or origin of the Caribbean bauxites.

Jan 1, 1984

By Clyde L. Smith

Since the early 1950's exploration in the Yukon Territory, Canada, has been confined largely to Selwyn basin where at least five large stratiform or massive sulfide Pb-Zn deposits have been discovered. The five ore bodies total nearly 100 million tons of 10-16% combined Pb-Zn with 1-3 oz./ton Ag. The only deposit currently in production is the Anvil Mine operating at 8,000 tons per day. Beginning in 1972, exploration in the Mackenzie Mountains, east of Selwyn basin and west of Mackenzie arch, resulted in finds of Mississippi Valley type Zn-Pb mineralization in a belt of Proterozoic and Lower Paleozoic carbonate rocks (Figure 1). Four districts have been located and intensive exploration by numerous Canadian and Arnerican mining companies is currently in progress over a length of 400 miles in the carbonate belt. The consensus is that a major new Zn-Pb province may be taking shape.

Jan 1, 1974

By L. S. Fountain

A national survey, 1978-1980, found 180,973 waste impoundments used by industrial mining, municipal and other interests. Possibly 27,000 contain hazardous materials. The potential hazard of leaks polluting water supplies is a growing concern. An electrical technique was developed to efficiently and speedily detect and locate leaks in geomembrane-lined liquid impoundments without emptying the contents. A potential applied between the liquid and earth causes electric current to flow through leaks in the insulating geomembrane material to ground. The cur- rent density around the leak is used to detect and locate the leak. Field tests show single and multiple leaks 2.54 cm in diameter or less can be detected and located to within less than 30 cm.

Jan 1, 1986

By Yun Bai, Ang Chen, Xiangdong Hu, Yanfei Zhu, Gang Li

"It is well known that tunnelling involves a high degree of risk. Conventional risk management only evaluates risks and chooses mitigation measures before the start of a project. However, mitigation measures also introduce risks, which are ignored in the conventional risk control process when choosing different measures. The Multiphase Risk Management Method (MRMM) takes the risk of mitigation measures and dynamic risk control into consideration. This paper introduces this new method and provides a flow chart for better understanding. A case study of the MRMM is given based on Ningbo Metro Line 3, the first quasi rectangle shield tunnel in China. INTRODUCTION Tunnelling itself is generally complex and involves a high degree of uncertainty (Huang, 2006; Thompson and Thompson, 2006). In recent years, several metro tunnel projects in China have been involved in accidents (Wang, 2006; Gong and Zhang, 2012).As a result, Chinese tunnel engineers are paying more and more attention to risk management in tunnel projects (Xiao-lin and Ping et al., 2009; Zhong and Jia et al., 2014), and scholars around the world have put forward many management processes. Existing risk management mainly focuses on a particular stage of a tunneling project. Tunnel engineers or other project parties usually carry out risk assessment and set up schemes or choose mitigation measures before a project begins. The risk from this initial risk assessment may be defined as the initial risk (Bai and Dai et al., 2013). This kind of managing process has been widely used for its simplicity and comprehensibility. However, this static theory cannot properly reveal the dynamic character of the risk during tunnelling. In addition, to reduce the risk from unacceptable level to acceptable level also calls for optimum measures. Therefore, the multiphase risk management method was proposed (Bai and Dai et al., 2013). The purpose of this paper is to introduce and develop the MRMM, and to provide a brief flow chart to illustrate the risk management process based on it. Finally, an example of the first quasi rectangle shield tunnel in China in Ningbo Metro Line 3 is illustrated. It analyzes the initial and secondary risk and sets up a risk control system."

Jan 1, 2016

By A. K. Sinha

Ever since electricity was introduced, electrical injuries and electrocutions have continued to occur regularly in coal mines. An analysis of the two hundred cases of electrocutions which occurred during 1956 to 1970 indicated that over 50 percent of the incidents were caused by the ineffectiveness or lack of electrical grounding. Research shows that various types of arbitrarily designed ground beds are in use and that the ground resistance and current are often very high and subject to wide seasonal variations. The results of a recent research are discussed in this paper.

Jan 1, 1980

By J. Keng, S. T. Chen, T. M. Shih

Kwanyin Tunnel is presently the longest (7.7 km) railway tunnel in Taiwan. Due to heavy railway traffic, a pass-by station will be built inside the tunnel to increase the traffic flow. Since the concentration of toxic gases released by the locomotives may reach dangerous levels, a research program was conducted for the purpose of designing a ventilation system which could dilute and/or remove the toxic gases to maintain an acceptable pollutant level. The program consisted of two parts. The first part was field measurement during which the concentrations of pollutants and wind velocities were measured at various points inside the tunnel to acquire basic data regarding ambient air quality, piston effects for the different types of trains, and existing ventilation conditions. Weather data (temperature, humidity, atmospheric pressure, wind direction and velocity) were gathered at many stations, both on the surface and inside the tunnel. The amount of pollutants released by each type of locomotive for various conditions were also measured. The second part of this study involved establishing mathematical models for predicting the air quality of the various proposed ventilation systems. Three different models were used for this work. The first one is a piston effect model which assumes that the gases and air undergo immediate mixing inside the tunnel. The second one is also a piston effect model which assumes that the diffusion ability of the gases is zero. The third one is a conventional ventilation model which was used for natural and mechanical ventilation conditions. From the result of field measurement and mathematical model studies, a ventilation system was chosen with consideration of both ventilation effects and construction costs.

Jan 1, 1987

By G. Argyris

A number of important studies, ongoing environment monitoring efforts and mining and road construction projects in the lignite based electrical power production area of Amyntaio ? Ptolemais in North West Greece require an accurate and up to date model of the topography. In recognition of the importance of such a model, a project was initiated by the Laboratory of Mining Information Technology and GIS Applications in the Department of Geotechnology and Environmental Engineering of the Technological Educational Institute of Western Macedonia. A massive surface triangulation model was generated from vector data using an optimized Delaunay based method. Combined with aerial and satellite imagery, the triangulation model provides a complete 3D terrain model of the area characterized by high levels of accuracy, detail and realism. The generated model is easy to modify with new data in order to improve its detail and keep it up to date with ongoing earth moving and development operations in the area.

Jan 1, 2008

By B. Denby

Recent advances in virtual reality (VR) have resulted in major opportunities for improving the safety training of mine workers, supervisors and managers. VR has the potential to expose mine personnel to hazardous situations in a safe, highly visual and interactive manner. Customized simulations of mine layouts, dynamic operations and mine environment can be set up, and mine personnel can be allowed to move around the virtual mine, making decisions at key points. The consequences of both correct and incorrect decisions can be immediately fed back to the trainee.

Jan 1, 2000

By Carol Cox Russell

More than two thousand abandoned mines within the Animas watershed in Southwestern Colorado are being prioritized for remediation by the Animas River Stakeholders Group (ARSG). Phased collection and assessment of information progressed from large scale to site specific. Prioritization was based on existing or potential environmental impact and technical feasibility of remediation as measured by dissolved Cd, Cu, and/or Zn in the discharge; indicators of habitat degradation; aquatic life in streams; cumulative impacts at the point of compliance; cost effectiveness; treatiblity/feasibility; and cultural and historic preservation.

Jan 1, 2000

By A. L. Mular

Optimization has been defined as the procedure of locating the best of something or the best way of doing something (Mular, 1971). Several texts (Himmelblau, 1972; Ray and Szekeley, 1973; Box and Draper, 1969; and Lee, Adams, and Gaines, 1968) on the subject are available. Such techniques have been placed in two categories, namely, off-line optimization and on-line optimization. For the former, an optimization model is employed; for the latter, a black box approach is involved. The essence of an optimization problem becomes obvious, when a response surface is considered. Suppose that a response (in this case, a criterion of improvement such as profit per day; grade of concentrate per day) denoted by Y, depends only on two variables, X1 and X2, which can be manipulated and controlled. The relationship between Y, X1 and X2 may be represented graphically as shown in Fig. 1. The diagram is called a response surface and its height, Y, is determined by X1 and X2. Points associated with equal responses constitute response contours. The shape is that of a hill, and optimization is the procedure of ascending the hill to reach the top (maximum). In practice, a response surface is subject to disturbances which distort its shape and shift its location from time to time, so that the exact location of a maximum is imprecise. Generally, constraints (restrictions of some sort) on responses and manipulable variables serve to define a region of permissible operation.

Jan 1, 1979

By Allan M. Hale

Taconite tailings reclamation, especially the stabilization of tailings ponds, .dams, and slopes, can be effectively accomplished through the use of appropriate vegetation. Utilizing vegetation provides both aesthetic and ecological enhancement of a site while at the same time protecting tailings structures against wind and water erosion. Generally, the methods and techniques for establishing vegetation are well known; however, there are many site-specific factors that can alter a particular reclamation approach. Those factors include slope gradient, tailings material size, solar exposure, and physical and chemical properties of tailings. In addition to the site-specific factors, variations in climate, geography, and physiography of a region can have a pervasive influence on the success or failure of a revegetation program. Both the site-specific and regional factors control reclamation planning in such areas as plant variety selection, methods and times of plants establishment, maintenance techniques, and subsequent monitoring methods. As a result of this multifactor relationship, it is important to establish a data base that identifies both the site-specific and location conditions in order to tailor the reclamation plan to the specific area. When an appropriate data base has been collected, detailing the various site-specific and regional factors that will influence a revegetation program (in the absence of previous testing), it is very beneficial to apply experimental techniques to develop the reclamation plan for a specific site. The reclamation plan for a specific site may include several techniques adapted for the differences found within the specific site as the result of topographic or other influences. Considering this, the Reserve Mining Company and Dames & Moore undertook to develop a successful reclamation plan based on a detailed test plot program conducted at the Mile Post 7 location.

Jan 1, 1980

Throughout the 1970s, the US Bureau of Mines rode an ebb tide in Washington political circles. In rapid fire succession, the agency lost its mine health and safety enforcement responsibility (1973), a large portion of its energy research responsibility (1975), and then its fuel statistics functions plus a sizable portion of its coal R&D (1977). By 1978, johnny-come-latelies in the Energy, Labor, and Interior Departments had siphoned away from the Bureau some $125 million in program responsibilities as well as 900 of its employees. The bruising decade came to a close with a Department of Natural Resources proposal that, in its original form, would have scattered the Bureau's responsibilities to the winds. "There is no doubt in my wind," said Lindsay Norman, acting director of the Bureau of Mines (see box), "that were the Bureau to continue down the path it was on, the next step was closing the doors and going out of business." The doors are still open, but erosion of responsibilities had a devastating effect on the resources available to fulfill the Bureau's mission. Devastating, too, in terms of internal morale, considering the Bureau had six directors in a 10-year span. "When the troops are in the trenches and are being shot at," Norman said, "they need a leader-hopefully, a permanent one- that can get them advancing. This is something the Bureau did not consistently have in the 1970s." In September 1978, Roger Markle climbed aboard as director of the Bureau to rejuvenate the 70-year-old agency. He resigned only six months later* but the program Markle set in motion is being carried through by Lindsay Norman. Since Norman's appointment as acting director, he has spent considerable time on the road explaining his agency's redefined goals. At one such stop in Duluth, Norman and his two deputy directors, Charles Kenahan and Mike Kaas, answered the following questions. Lindsay, you were the principal architect in the Bureau's 1979 reorganization. How about a glimpse of what that entailed? Toward the end of the 1970s, after almost a decade of steady dismemberment, we reached what we felt was a critical point in the Bureau's history-we had the choice of redefining and strengthening our organization to meet the mineral challenges ahead, or continuing down the path toward the agency's eventual demise. We felt the Bureau's mission too important to abandon, so in 1978 with Roger Markle as director we initiated a six-month, no-holds-barred intro spection of just what the Bureau should be doing, why, and toward what ultimate national needs. And what did this self-reflection reveal? That there is, indeed, a unique federal role for the Bureau of Mines-that of a lead agency for influencing mineral decisions and pioneering tomorrow's technologic advances. Don't confuse us with policymakers, we're not. But we are policy analysts; we're scientists, engineers, and mineral professionals who can offer a sorely needed source of objective, accurate information to decision makers in both the public and private sectors. I feel there is no better brain trust in government than the Bureau when it comes to mineral expertise-of course, I'm biased. Do I understand you to say the Bureau of Mines is an advocate agency for the minerals industry? We plead no parochial interests, nor ought we, but from our viewpoint a sound minerals industry is extremely important to the broader national goals of security and a healthy economy. US dependence on foreign sources for critical minerals, the increasing noncompetitiveness of some US mineral sectors, and the array of land use issues surrounding mineral-rich lands all have much more serious implications than many otherwise informed people seem to recognize. In your estimation, how vulnerable is the US to foreign mineral suppliers? Let me make a distinction between dependency and vulnerability. The

Jan 4, 1980

By William Lodding

That grinding may change a crystalline material both in a physical and in a chemical sense has been shown by a number of authors in recent years. Thus Mackenzie (1) and Bartha (2) reported the effects of careful grinding on muscovite, quartz, gypsum, dolomite, etc. Increase in specific surface produced by grinding implies increase in total energy of a system. Newly produced surfaces are chemically more reactive; dislocations may be introduced during grinding, and existing strain may be released by the same process, as shown by Holt et el. (3) All these changes are easily detected by thermal analysis, but it is not easy to separate the multiplicity of effects registered and to arrive at quantitative interpretations. This paper is an attempt to analyze by the use of thermal analysis some effects produced in grinding. In differential thermal analysis (DTA) one measures all thermal changes occurring in a substance during heating or cooling. Chemical changes, such as decompositions, synthesis, oxidation, reduction, etc., and physical changes such as phase transformations, changes in specific surface and in thermal conductivity, strain release, etc. By thermo gradmetric analysis (TGA) on the other hand only chemical changes involving weight loss or gain are recorded. Similarly gas evolution analysis (GEA) will register only reactions involving gas evolution, including water vapor, and oxidation-reduction. By performing two or all three of these thermal methods of thermal analysis simultaneously and on the same specimen one can separate the different effects registered and by difference evaluate their magnitude.

Jan 1, 1966

By K. Fuenkajorn, S. Serata

Discussion by S. Serata and K. Fuenkajorn 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, Gardnerand 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. Stress measurement The key issue is how to form the global stress envelope to make the gate entries safe for production. Therefore, measuring the stress condition of the ground around the mine opening is critically important to solving the cutter-roof problem, regardless of the method applied. With regard to the stress measurement, there is a serious question as to the reported stress state of [6 i = -51.7 MPa (-7499 psi), G2 = -44.5 MPa (-6458 psi) and 63 = -30.8 MPa (-4465 psi)]. It is mechanically impossible to have such a stress state at any location in the mine ground since the known initial vertical stress [o,,] is less than or equal to 800 psi. There may be a large stress state in the [61] direction, but that is possible only at the expense of the [63] value. Having the above stress tensors in the mine is simply impossible. The questionable, reported stress values could be attributed to the application of the overcoring method, which tends to produce erroneously large stress values in the extremely nonelastic mine ground. Stress control method The paper should be considered as a major contribution demonstrating the limitation of the yield pillar method. At the same time, the paper does not disprove the stress control method. However, in comparing the paper with stress control studies conducted in other similar failing grounds, the stress control method appears to be able to solve the problem more effectively. Therefore it is advisable that the mine not give up its efforts to solve the problem. [•] References Serata, S., 1976, "Stress control technique - An alternative to roof bolting?," Mining Engineering, May. Serata, S., 1982, "Stress control methods: Quantitative approach to stabilizing mine openings in weak ground," Proceedings, 1st International Conference on Stability in Underground Mining, Vancouver, BC, Aug. 16-18. Serata, S., Carr, F., and Martin, E., 1984, "Stress control method applied to stabilization of underground coal mine openings," Proceedings, 25th US Symposium on Rock Mechanics, Northwestern University, June, pp. 583-590. Serata, S., and Gardner, B.H., 1986, "Benefits of the stress control method," invited paper, American Mining Congress Coal Convention, Pittsburgh, PA, May 7. Serata, S., Gardner, B.H., and Shrinivasan, K., 1986, "Integrated instrumentation method of stress state, material property and deformation measurement for stress control method of mining," invited paper, 5th Conference on Ground Control in Mining, West Virginia University, Morgantown, WV, June 11-13. Serata, S., and Kikuchi, S., 1986, "A diametral deformation method for in situ stress and rock property measurement," International Journal of Mining and Geological Engineering, Vol. 4, pp. 15-38. Serata, S., Preston, M., and Galagoda, H.M., 1987, "Integration of finite element analysis and field instrumentation for application of the stress control method in underground coal mining," Proceedings, 28th US Symposium on Rock Mechanics, Tucson, AZ, pp. 265-272.

Jan 1, 1993

By S. E. Restrepo

To innovate and make the operation sustainable it is necessary to identify the externalities and impacts completely. This paper presents the results of a proposed methodology to make circular economy initiatives viable in mining operations using these aspects: • Economic, safety, and environmental (HSE) risk analysis • Technology observation • Mineralogical characterization • Identification of potential waste uses • Use of government economic benefits The results of the project can be summarized as follows: • Implementation of new technologies in the aggregates process, • efficient use of water, • the valorization of waste to convert it into a by-product, • and access to tax benefits for investment savings.

Mar 2, 2022

By Jan K. Wolski

This paper addresses jet fans used as booster fans within mine ventilation networks. The static pressure developed by the jet fan was determined using the momentum theory. The influence of various parameters on this pressure was analyzed. A method was proposed for determination of the jet fan characteristic curve . The distance between the jet fan and a point where the fully developed static pressure can be measured was determined. It was shown that a reduction cone can significantly improve the jet fan performance. Verification experiments conducted in the Waldo mine are described.

Jan 1, 1995