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By J. West-Hansen

The problem of long-term production scheduling in an underground coal mine is approached through the concepts of sequencing theory. Based on a typical layout of mining sections, the principles for the approach are: 1. The definition of mining sections as jobs, and mining methods as machines. 2. The reduction of the overall mining activity to the general problem of nonpreemptive scheduling of precedence related jobs on parallel machines. 3. The simplification of the layout to a general type directed network with the nodes representing jobs and the arcs representing precedence relations. 4. The determination of a feasible and near-optimal job schedule given the objective of maximizing the total net present value of the jobs. A general scheduling heuristic is being developed for implementation on an IBM personal computer (PC) as part of an interactive computer system for long-term production planning.

Jan 1, 1986

By Christopher J. Bise

INTRODUCTION The level of analysis for the selection of extraction practices and equipment for surface mining differs significantly from that found in underground mining. In underground mines, manufacturers establish the operating ranges of the equipment, such as continuous miners, loaders, and boring machines, based upon required clearances. Even in conventional mining, the drilling and blasting operation is usually based upon experience. The selection of extraction methods and equipment for surface mining is more complex. Since the equipment is not as confined as in deep mining, and the topography tends to be highly variable over the limits of the mining property, primary extraction equipment must be sized according to reach and capacity. Further, due to the depositional characteristics of the over- burden, drilling and blasting patterns must be well- designed to provide proper fragmentation. The following sections provide a general outline for the selection of surface excavation practices and equipment. The topics covered include drilling and blasting and the selection of both primary extraction equipment (draglines and stripping shovels) and secondary extraction equipment (bulldozers, scrapers, and front-end loaders). EXCAVATION FUNDAMENTALS Before discussing surface excavation, a few concepts need to be defined. A bank cubic yard of material is equal to one cubic yard as it lies in its natural or undisturbed state. A loose cubic yard is that portion of a bank yard that after being disturbed has expanded to measure one cubic yard. Swell is the volume increase of a material when it is removed from the natural state. Finally, load factor is the percentage decrease in the density of a material from its natural state to a loose state. Table 1 summarizes these concepts for various materials. When the amount of overburden to be removed to meet a predetermined production rate is established, a suitable bucket size for the primary stripping equipment must be calculated. The following equation can be used: NBSIZE = TBC/[(OF) (BF)] (1) where NBSIZE is the actual bucket capacity after considering the swell percentage, the bucket fill factor, and the operating efficiency; TBC is the theoretical bucket capacity (TBC = COB/NTCPM); OF is the operating efficiency; BF is the bucket fill factor; COB is the cubic yards of overburden to be removed; NTCPM is the number of theoretical cycles per month [NTCPM = (SMH) (3600)/(CT)]; SMH is the scheduled monthly hours; and CT is the cycle time in seconds. FRAGMENTATION PROCEDURES Drilling Where the strength of overburden material is such that blasting is required prior to excavation, drilling is conducted before using explosives. Two methods of drilling are found in mining-percussion and rotary. Penetration of overburden by percussion drilling is carried out by successive impacts of the bit into the rock. Emphasis in this section will be placed on rotary drilling, because for surface mining it is the most versatile form of overburden penetration. Rotary drilling is conducted by rotating a rigid string of tubular rods to which a rock-cutting bit is attached. The drilling energy is supplied by rotation as well as thrust and the cutting action consists of abrasion, scraping, spalling, or chipping. The size range for rotary-drilled blastholes is from 4 in. to 15 in., with 9 in. and 12 in. being common sizes. There are two types of bits used for rotary drilling-drag and rolling cutter. Drag bits are applicable in soft to medium-soft shales or their equivalents. Since their effectiveness is dependent upon a successful scraping action, drilling thrust is lower for drag bits than for rolling cutter bits; the opposite is true for torque requirements. The bits are usually fitted with replace- able tungsten-carbide cutters. Rolling cutter bits, though available in a two-cone configuration, are usually of the three-cone style (Table 2). The rolling cones have either large steel teeth for drilling through soft formations or small tungsten-car- bide inserts for drilling through hard formations. Table 3 relates bit size and weight to the strength of the rock. The major advantage of rotary drilling is its rapid drilling rate. This is due to the fact that, unlike percussion drilling, rock penetration is uniform with depth. Blasting Effective bank preparation deals not only with the fragmentation of overburden but also with the mini-

Jan 1, 1986

By Craig M. Sams

Phosphate mines in Florida are continuing to encounter higher dolomitic content host rock with the phosphate pebbles(1) necessitating a change in grinding conditions and/or circuits, One of these changes is to install hydrocyclones and close circuit the mill as opposed to the traditional open circuit grinding plant. Close circuiting of the grinding mill with hydrocyclones allows one to take advantage of reduced process mill power requirements by circulating the coarse mill discharge back into the mill for multiple chances of particle breakage. Additionally, as in this case, the hydrocyclones de-slime the pebbles, allowing for more efficient use of grinding power by reducing the amount of dolomitic material recycled to the mill.

Jan 1, 1986

By K. Taniguchi, Y. Inada

When underground openings are excavated in rock mass for storage of Liquefied Natural Gas, hereinafter referred to as L.N.G., as its temperature is -162o C, steep temperature gradients and thermal stress occur around the openings. That is, the plastic zone and cracks around openings will expand with time. In this paper, the range of cracks which were obtained by the Crack Analysis Method and the range of the plastic zone which was obtained by the No Tension Analysis Method were investigated and compared.

Jan 1, 1986

By Dae S. Young, Steven F. Hoerger

The geostatistical method of indicator kriging (IK) was extended to analyze two-dimensional distributions of rock joint orientations. The IK method provides a non-parametric approach for spatial analysis of local probability distribu- tions. By taking into account the spatial correlation of rock joint outcomes and the relative geometry between estimation unit and samples, the IK method provides optimum, spatially conditioned estimates. The estimation method was tested by comparing distributions of actual mapped rock joint orientations with their corresponding kriged estimates. The comparisons show the unbiasedness and accuracy of the non-parametric approach for estimating local probability distributions.

Jan 1, 1986

By Ralph W. Barbaro

This paper presents a cyclic queueing model which evaluates the productivity of a shovel-truck materials haulage system. For a cyclic queueing problem with exponentially distributed service times, a cyclic queueing model provides exact solutions in a fraction of the time that simulation takes to produce an approximate solution. The model is applied to an example problem, and the results are validated with simulation. Simulation is used to show that the assumptions of exponentially distributed service times and steady-state are not serious problems. A cyclic queueing model can be used to quickly obtain an accurate assessment of the productivity of a shovel-truck system.

Jan 1, 1986

By R. C. Jr. Babcock, V. S. Znamensky

The Pyke asbestos deposits were discovered by Kennecott Explorations (Australia) Pty. Ltd. in 1969 during the course of base metal exploration on the South Island of New Zealand. Extensive occurrences of chrysotile asbestos were found associated with the Red Mountain ultramafics in the headwaters of the Pyke River, and to the north and south along the ultramafic belt for a distance of 70 km. Surface evaluation and drilling by Kennecott in 1970 and 1971 identified numerous small deposits of good grade fiber in the Little Red Hills between the Pyke and Barrier Rivers. Additional drilling and three adits have been completed by other companies since that time. The property is presently held by Lime and Marble, Ltd., of Nelson, New Zealand, and Kennecott Explorations (Australia) Pty. Ltd. This chapter presents the regional and local setting of the asbestos deposits, including the geology and nature of mineralization. In addition, the exploration methods used by Kennecott in the discovery and evaluation of these deposits are outlined. Subsequent work by other companies is mentioned, but not de- scribed in detail. This subsequent work did not alter Kennecott's conclusions or produce any serious changes in the interpretation of geology and mineralization. The author acknowledges the contribution of the many employees of Kennecott Explorations (Australia) Pty. Ltd. who have been involved in the project. In particular, thanks go to Ramon Farmer, N.G. Corner, and A.W. McConie, who were responsible for completion of field work and reporting on the project. The responsibility for the conclusions and interpretations of this chapter are solely that of the author and result from his involvement in the discovery of the deposits and management of the exploration program. REGIONAL SETTING Ultramafic rocks on the South Island of New Zealand are thought to be Permian in age and occur between crystaIline and metamorphic continental rocks of Precambrian through Cretaceous age in the west, are thought to have once been part of the Antarctic subcontinent, and the extensive geosynclinal graywacke deposits of the Mesozoic New Zealand geosyncline in the east. They consist of the Dun Mountain ultramafics, a 130 km long segment of ultramafic rocks located at the north end of the South Island, and the Red Mountain ul- tramafics that occur in a zone 200 km long in the south half of the South Island as shown in Fig. 1. These two belts, once contiguous, have been offset a distance of 560 km by the still active Al- pine fault, which is analogous in character and offset to the San Andreas fault of the United States. The ultramafic rocks occur within a sequence of Permotriassic volcanic and sedimentary rocks that probably formed at the eastern margin of the continental plate. The ultramafics appear to be tectonically emplaced between Permian lithologies in the Dun Mountain belt (Coleman, 1966), and at the base of or between Permian volcanics and sediments in the Red Mountain belt. The Permotriassic ultramafic volcanic sequence of the Red Mountain ultramafic belt appears to be a typical ophiolite sequence. Ultramafic rocks, mixed mafic intrusive rocks and volcanics, volcanic rocks, and volcanoclastic sediments occur in apparent superposition from east to west in the area of Red Mountain. Farther south, ultramafic rocks are associated with basaltic volcanic rocks and some sediments, and still farther south are emplaced entirely in sediments. These structural compIications of the normal ophiolite sequence have resulted from the coincidence of Permian subduction, early Mesozoic extension and sedimentation, and Cretaceous subduction along the same plate margin (Landis and Bishop, 1972). The general geology in the area of the Red

Jan 1, 1986

By Donald D. Born

Mine No. 95 is located in Harrison County about 5 miles west of Shinnston, WV, with coal properties covering the northwest corner of Harrison County and the southwest corner of Marion County and with adequate Pittsburgh seam reserves to support the mine for many years. The mine was opened in 1967 and was planned, projected and operated as a room and pillar mine. It is located on a spur branch of the Baltimore and Ohio Railroad, has rail loading facilities and shipped by rail during its development stage. In 1972 it was converted to a mine mouth power station supplier and now transports coal by conveyor belt directly to the Harrison Power Station of Allegheny Power System. In 1971 the first longwall unit was installed in a selected area of the mine and immediately an orderly system of planning was developed to overcome the restrictions associated with longwall mining. The first was the development of the technique necessary for the plugging of abandoned oil and gas wells that existed in the area. With the assistance of the Morgan- town Energy Research Center of the Bureau of Mines, this restriction was overcome and thus opened a great potential for longwall mining in northern West Virginia. Other restrictions that had to be considered for longwall planning were dwellings and other improvements, snap top zones, water courses, and adequate bleeder systems, and the handling and treatment of mine drainage. In 1975 the second longwall unit was installed and soon therefore became a total longwall mine.

Jan 1, 1986

By H. G. Fleshman

Thousands of years ago, Chinese water well drillers developed a technique for punching holes in the ground by lifting massive metal bits and letting them fall against the rock. With diligence, they could pound away about 2 feet a day. The Chinese drillers pounded holes in the ground this way for almost 2000 years. In the 1860's, French water well drillers developed a perforated bit moistened by fluids pumped into the hole through a hollow rod. The fluids carried the cuttings from the hole and spared the Frenchmen the task of bailing them out by hand.

Jan 1, 1986

By J. -C. Roegiers, M. Thiercelin

Accurate toughness determinations are difficult to achieve in the case of soft or heterogeneous rocks. The existence of a large process zone ahead of the crack tip makes the determination of the apparent toughness crack length dependent, in the case of subsized specimens. In order to use practical size specimens, the authors propose a new toughness test, the Modified Ring Test, which pre- vents a largely developed process zone to form ahead of the crack tip. This test has also the advantage that its geometry is core-based. Numerical and experimental results are discussed.

Jan 1, 1986

By P. Bartel

Coal cleaning can be effected by the bacterium Sulfolobus acidocaldarius, which in oxidizing sulfur and dissolving mineral matter requires carbon dioxide and oxygen; carbon dioxide as a carbon source and oxygen as an electron acceptor. The desulfurization of coal by thermophilic bacteria under elevated partial pressures of carbon dioxide and oxygen was studied at a total pressure of 1 atm. The partial pressure of carbon dioxide was varied over the range 0.00032 to 0.33 atm (0.00032, 0.007, 0.10, 0.33 atm), and the partial pressure of oxygen was varied over the range 0.14 to 0.40 atm (0.14, 0.21, 0.30, 0.40 atm). The maximum rate of coal desulfurization increased by 32%, from 9.0 to 11.9 mg S/1 hr, as air was enriched in carbon dioxide from its atmospheric level of 0.00032 atm to 0.10 atm. Enrichment with carbon dioxide up to 0.10 atm, at constant oxygen partial pressures, increased the desulfurization rate, but enrichment to 0.33 atm caused the rate to decrease. At constant carbon dioxide partial pressures, the desulfurization rate was maximum at oxygen partial pressures of 0.21 and 0.30 atm. At higher (0.40 atm) and lower (0.14 atm) oxygen partial pressures the rate decreaed by 9 to 20%. The desulfurization rate decreased by 58X, from 9.0 to 3.8 mg S/1 hr, when the air pressure was increased from 1 atm to 3 atm. The effects justify an economic analysis during design and operation of a commercial air feed in a process to desulfurize coal by microbial action.

Jan 1, 1986

By Charles D. Litton

Introduction The successful performance of a mine-wide fire detection system depends upon its ability to detect the presence of a fire rapidly and reliably. It should be sufficiently rapid so that there remains enough time to either safely evacuate a mine or successfully extinguish and control the fire or both. It should be reliable so that false alarms are minimized without sacrificing sensitivity or time response. Systems should also be durable enough to withstand the mine environment over long periods of time while maintaining a high degree of re1iability. Maintenance and calibration of the system should be simp1 e and not require the expenditure of excessive time and manpower to keep it operational. Sensitivity, reliability, and durability of mine fire sensors and their electronic support systems have been the subject of significant Bureau research within recent years. The bulk of this type of information, along with the reports from which the remainder of this paper is derived, can be found in the Bibliography. It suffices to say that there exist commercially available systems for use in mines. This paper addresses a strategy for the use of such sensors and systems. Many factors influence the design of a mine-wide fire detection system, such as the potential sources and modes of ignition, the types of combustibles involved and the quantities avai1able for fire growth and flame spread. Mine air ventilation influences the growth and spread of a fire and also serves to transport the products-of-combustion to other areas of a mine remote from the fire. Fire sensor alarm thresholds place limits on the sizes of fires that can be detected. The time to respond to a detected fire, either in terms of evacuation or control and extinguishment, place additional time constraints on the design of fire detection systems. These factors interact with each other, often in complex ways, and it is the definition and understanding of these factors and their interactions that hold the key to the design of adequate and re1iable fire detection systems. Our level of understanding of the problem has increased dramatically within recent years and it is the intent of this paper to discuss the progress that has been made and how the information can best be used to improve the level of fire detection in underground mines.

Jan 1, 1986

By Qing-Wang Hao

In this paper, the authors attempt to develop engineering based approaches for estimating safety factors against pillar and floor failures and predicting likelihood of subsidence events over abandoned coal mines in Illinois. There are two critical problems involved in the analysis: determination of geotechnical properties, and consideration of time effect. The authors attempt to solve the problems by generating hypotheses, which are used to modify existing engineering models for estimating pillar and floor safety factors. The modified models are validated using data from two well established databases of subsidence events over active and abandoned mines in Illinois. The data analysis suggests that most of the trough type subsidence events in Illinois were caused by floor failures rather than pillar failures. The subsidence incubation period seems to be directly related to initial floor safety factors at the time of mining. This correlation can be used to predict the likelihood of subsidence and to assess subsidence risks within both spatial and temporal contexts where detailed mine maps are available.

Jan 1, 1986

By Richard K. Thorpe, Francois E. Heuze

The concept of a reusable underground nuclear test facility, named HEDEF, has been under study for some time. This rock chamber would have to be engineered to sustain the repeated mechanical and thermal shocks of internal explosions. In this paper, we summarize preconceptual studies performed in support of HEDEF, including -simple dynamic calculations for internally loaded tunnels, -outline of proof-of-concept tests of proposed reinforcement, - and initial dynamic testing of reinforcement components in an underground high explosive (HE) test.

Jan 1, 1986

By M. S. Basich, J. S. Scope1, J. H. Raeder

During 1983, The Youghiogheny and Ohio Coal Company's lost-time-incidence rate was 8.1, equal to the average for underground bituminous operators. How- ever, one half of all lost-time injuries were low back, back and neck related. In reviewing these results, we determined that substantial improvement could be made. We investigated existing back schools and the possibility of opening an in-house clinic. In September 1984, we began The Youghiogheny and Ohio Coal Company's Back Care Program. The objectives of the program are to reduce the number of back injuries incurred at the work site, hasten recovery time, decrease medical and workers' compensation costs and provide the employee with a thorough understanding of his problem. A state-of-the-art clinic capable of treating injuries to the spine and extremities has been established at the work site. The clinic is staffed by a licensed physical therapist and is offered to all employees on a voluntary basis under physician referral. The approach to treatment is multi-phasic. For the typical patient, the initial goal is to reduce pain and correct dysfunction. Treatment modalities such as auto-traction, extension exercises, ultra sound and moist heat are frequently used. During this period the patient is given extensive education regarding his problem. As soon as more vigorous activity can be tolerated, a work-hardening pro- gram consisting of job simulation activities designed to improve flexibility, strength and functional capability is begun.

Jan 1, 1986

By Thomas S. Mackey

The industrial types, sources, and quantities of USA tin residues are identified and the methods of treatment reviewed. The effect of a lower tin price, due to a current major world surplus of tin metal, is mentioned and covered in some detail. The names and locations of over 100 USA firms recovering tin residues are listed. Current smelting and refining charges are included to convert the residues into tin metal and alloy. The impact of the suspension of the LME daily tin price since October 24, 1985 to date, and the failure of the International Tin Council to support the Buffer Stock Manager are reported with comments.

Jan 1, 1986

By K. Katen

In another situation, Dave Zegeer, the Assistant Secretary of Labor for Mine Safety and Health, whom all of you know very well, would have taken the opportunity to talk with you. In his absence, however, I would like to reference some of his recent comments which may help us to see the issue of mine safety in historical perspective. Dave pointed out that this year is the eightieth anniversary of the Great Earthquake and Fire of San Francisco. The whole world heard about that disaster--it and the 452 people who died in it. In that same year, nearly five times as many people died in coal mines, but no one particularly noticed.

Jan 1, 1986

By D. Robert Weir

The complex mineralogy of the Porgera resource has a pronounced effect on process selection for the recovery of refractory gold and silver. Intimate association of gold with pyrite necessitates a high degree of sulphur preoxidation in order to achieve acceptable levels of gold recovery. Acid pressure oxidation has been demonstrated to be the only commercially proven process capable of achieving the required level of pyrite oxidation. Gangue mineralization dictates preconcentration of the sulphides to limit the acid consuming capacity and carbon dioxide generation during oxidation. However, the relationship between concentrate sulphur grade and gold recovery to concentrate ultimately governs the optimum degree of sulphide preconcentration.

Jan 1, 1986

The effect of the chemical composition of pulverized bituminous coal particles on their physical transformation during the initial stages of combustion has been investigated. The results suggested that cenosphere formation does not require extensive thermal decomposition of the coal particles. The vitrinites in the bituminous coal softened earlier and developed larger cenospheres than the othe macerals. The coal particles swell to a higher extent during combustion than in pyrolysis; however, the cenospheres formed in the former process experienced a higher extent of fragmentation. The development of microporosity occurred predominantly after the resolidification of the swelled char particles. The type of macerals originally in the coal did not significantly affect the microporosity of the chars. Conversely, the morphology and anisotropy of the chars were strongly dependent on the maceral composition of the coal.

Jan 1, 1986

By L. Vandamme, J. H. Curran

A fully three-dimensional hydraulic fracture propagation model, based on the Displacement Discontinuity Technique, is briefly described. Using this model, it is shown that the geometry of a propagating fracture is dependent on several factors, among which the fluid pressure distribution within the fracture plays an important role. The containment of hydraulic fractures is found to be dependent on stress and toughness barriers in the formation. Containment is also observed to be more effective with a decrease of the viscosity, pressure or flow rate of the injected fluid. The three-dimensional layout of the fracture is shown to have a definite influence on the width and pressure distributions within the fracture. The examples considered indicate the need for fully three-dimensional models, as complements to the commonly used two-dimensional and pseudo-three-dimensional models.

Jan 1, 1986