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By Y. C. Kim

An alternate development drilling strategy to the one currently in use at the nine was investigated using geostatistics for a portion of the pit. The study area consisted of 4,000' x 5,000' in plan and 1,080' in elevation. The massive orebody, the three-dimensional nature of the problem, and the location of ultimate pit limit in the study area all created some unique problems in devising the development drilling strategy, as compared to the two-dimensional tabular deposits such as coal deposits. Rather than using the confidence interval of the global reserve estimate as the main criterion for development drilling, the confidence interval of short and medium range mine planning blocks was used as the objective. Based on somewhat arbitrarily selected level of confidence, the results from this study showed that a total of 50 DDHs rather than the planned 62 DDHs is sufficient in the study area, if the selected confidence levels are acceptable to the management. This paper also emphasizes the importance of the particular objectives being used in development drilling and how they influence the "optimai" place- ment of the development drill holes.

Jan 1, 1981

By G. D. Naugle

Deep open-pit mines invariably affect the local and regional hydrologic systems. Pit dewatering, occurring during mining operations, puts an obvious hydrologic stress on these hydrologic systems. However, post-mining hydro-logic impacts resulting from the pit refilling with ground water following the cessation of mining activity can also be significant. Prediction of the rate at which the post-mining pit will fill with ground water is a critical aspect of assessing such long-term hydrologic impacts. Numerical ground-water flow modeling prov1des a method that can be used to predict the rate at which pits will fill with ground water.

Jan 1, 1992

By Paul E. Scheerer

Synthetically produced magnesium hydroxide serves as the precursor for much of the magnesium oxide produced in the world today. Magnesium oxide, in a variety of physical and chemically reactive forms, is a very important commodity. It is used as the main component in refractories employed in steelmaking furnaces and in many base metal refining furnaces. In the chemical industry, it serves as a raw material in the production of epsom salts, rayon acetate, oxychloride and oxysulfate cements and magnesium sulfonates. It is a minor component in fertilizers and animal feeds. It serves as the starting material for producing fused magnesia, used as an electrical insulator in electric heating elements. It is employed in the magnesium sulfite process for pulp digestion in the paper industry. Additional uses are in SO2 scrubbers, as a neutralizing agent in the tanning industry and as a component in rubber compounding. Magnesium oxide is produced not only from synthetically produced magnesium hydroxide. It is produced from natural magnesites, natural brucites, and natural and synthetic hydro-magnesites. Synthetic magnesium hydroxide, as a starting material provides more control of the chemical purity and chemical reactivity of resulting magnesium oxide products because of the uniform nature, chemical and physical, of the hydroxide that can be produced. Synthetic magnesium hydroxide is produced by precipitation of Mg (OH)2 from magnesium chloride bearing seawater or natural brines through the use of a base such as Ca(OH)2 or NaOH.

Jan 1, 1978

By D. Nilsson, B. Aaro

To find out if there are any potential savings in "in-the-wall haulage for open pits," the Swedish companies ASEA and Kiruna-Truck in 1984 gave us financial support to study this solution in more detail. In the study, the use of in-the-wall haulage was studied for three hypothetical open pits with different sizes and shapes. Annual ore production rates also varied. A part of this thor¬ough study was published by the Swedish Mining Research Foundation (see Report F 8444, "The Use of Electric Trucks and In-the-Wall Haulage in Open-Pit Mining," in Swedish with an English Summary). Although in-the-wall haulage is of interest in some open pits, the local terrain is important for profitability. The authors do not think in-the-wall haulage is of any major interest for the mining industry. The following is a summary of some of the author's findings. To place the haul road in the wall is not of interest in open pits with declining metal contents in the bedrock. In such mines, the volumes from the haul roads will not yield reve¬nues. The cost per m3 for an underground haul road is much higher than for a haul road in the pit. This means that it is only of interest to place the haul road in the wall when mining gets deeper than about 50 m (165 ft). In-the-wall haul roads will reduce flexibility in the pit, and it will make necessary the use of smaller equipment with lower productivity and higher costs per ton. As Hustrulid, et al. show (Table 4), excavation savings of material hauled are very low, $0.10 to $0.25/t (0.09 to 0.27 per st). The extra operating cost, due to lower productive equip¬ment, will normally be much higher and thus destroy the whole idea with in-the-wall haulage. If electric trucks are profitable for in-the-wall haulage, it is normally also profitable to use electric trolley assist for trucks on the haul road in the pit. But the profitability of using electric power is different in different countries, and depends on the relation between the cost for electric power and diesel fuel. In the US, diesel fuel is inexpensive compared with electricity, but in a country like Sweden, diesel fuel is much more expensive. In most open pits, the trucks have to move a considerable distange from the loader until they reach a final haul road in the wall. A trolley line along such temporary haul roads will be exposed to flyrock. It is normally less expensive to perform rock support from the open pit than from underground ramps in the wall. In Fig. 8, Hustrulid et al. gives the impression that the underground haul roads will be very close to each other. This is seldom the case. Figure 1 shows a haul road in the wall. The haul road passes through each cross-section only once. Ar¬ranging a reliable dewatering and rock support system from only one underground ramp is probably impossible. Many more drifts are therefore necessary. In our report, we also studied what would happen if the final pit slope is increased by 5°, using underground drifts in the wall. Our conclusion was that the extra cost for drifts, rock support, pumps, etc. destroys the whole idea, and that it was better to accept a higher stripping ratio with the haul road in the pit and to use conventional low-cost open pit equipment. Finally, we think it is would be difficult to try to reduce the safety factor when determining the slope angle by moving the haul road in the wall. Minimizing the risk for pit wall collapse is also important with in-the-wall haulage, primarily because men and equipment will be working in the pit, but also to guarantee many accesses between the pit and the haul road in the wall.

Jan 1, 1989

By K. C. Vories

Surface mining and reclamation has the potential to at least temporarily increase surface runoff and resultant erosion and gully development. This increase in erosion is due in part to compaction of the soil surface with heavy equipment, creation of large relatively unvegetated watersheds, and elimination of natural dendritic ephemeral drainage patterns. Methods for stabilizing gully channels which may develop prior to establishment of sufficient vegetation to control erosion are analyzed. Utilization of various sizes of riprap for channel lining, the use of riprap check dams, reinforcement of riprap check dams, and the relation- ship of type of control structure to area of watershed and resultant flow velocities are discussed.

Jan 1, 1986

By A. E. Ketler

Optical smoke monitoring fills an important gap in ventilation and fire safety: namely monitoring of smoky, low temperature fires where little CO and heat are generated. Smoke monitoring also avoids the nuisance alarms due to diesel exhaust, battery chargers, blasting and welding. The smoke optical density (OD) fire alarm standard specified by MSHA presents an opportunity for improved safety. Experience of actual mine usage of the SmokeBoss*100 is reviewed, with particular regard to effectivity, maintenance and cost.

Jan 1, 1995

By P. N. Eksteen, G. E. Greig

The South African mining industry currently installs about 6 km per month of plastic pipes for conveying compressed air and water. Plastic pipes have a number of desirable properties and are favoured by many mining engineers because of their low mass, which facilitates ease of erection and assembly, and their excellent corrosion resistance and durability. However, they are combustible, and if involved in an underground fire can contribute to the overall toxicity of the combustion gases emitted. Furthermore, plastic pipes have the potential to conduct a fire from one part of a mine to another, and, by so doing, exacerbate an already hazardous situation. The limitations of small scale tests and the need to establish a large facility where underground conditions could be simulated was recognized by the South African mining industry. This paper briefly describes the Industry's full scale fire test facility and presents the conclusions drawn as a result of a number of full scale combustibility tests conducted on pipes manufactured from unplasticized Poly Vinyl Chloride (uPVC) and High Density Polyethylene (HDPE). Based on these findings, some practical solutions to prevent the spread of fire along the length of pipe columns of various pipe diameters and suspension configurations are presented. Recently some new and exciting developments in the field of intumescent coatings have occurred which are proving effective in minimizing the incidence of fire underground on South African mines. The potential benefits of these coatings are briefly discussed. INTRODUCTION Plastic pipes used underground on mines are predominantly in the form of protective cladding on insulated chilled water pipes and as service pipes for the conveying of water and compressed air to the workings. Plastic pipes have found wide use in the aggressive environmental conditions encountered underground due to their favourable properties relative to steel; these include being lightweight, easily installed and virtually immune to corrosion. However, plastic pipes are inherently combustible and can contribute to the overall hazard in three ways: (i) they are easily ignitable and can provide the initial fuel for a fire. (ii) once ignited, they can propagate a fire along their length and by so doing ignite other combustibles in their path, thereby contributing significantly to the overall conflagration. (iii) they can contribute to the overall heat, smoke and toxic gas emissions from a fire. While conscious of the value of small scale fire tests, the South African mining industry recognized the need for full scale testing to determine the combustion characteristics of plastic pipes under conditions closely approximating those underground and, as a consequence, a full scale fire tunnel test facility was commissioned with the objective of being able to (a), accurately evaluate the potential hazard of the various types of the plastic pipes found in mines, (b) use this information to suggest suitable fire engineering practices to minimize the hazard and (c), to practically verify the efficacy of the practices suggested. THE FIRE TUNNEL The fire tunnel is situated on a mine in the Western Transvaal and is 40 m long with a cross section of 3 m x 3 m which is typical of many haulages currently in use in South African gold mines. The ventilation drawn through the tunnel is provided by a 110 kW centrifugal exhaust fan and air velocities can be varied from 0 to a maximum of 5,8 m/s.

Jan 1, 1993

By Ronald E. Feltman

Most engineering firms engaged in the design and manufacture of milling components and systems have established, through the years, a relatively well defined system design procedure. The process design engineer has at his disposal several alternative approaches to the successful completion of this task. Unfortunately, while these alternatives, at first glance, appear to be rather straight Forward, any attempt to implement them into a fully integrated commuter design program becomes increasingly more complex when one addresses himself to the problem in total. This paper summarizes Kennedy Van Saun's approach to the solution of this problem through a planned system design. Following the problem definition and discussion, a detailed analysis and system design synthesis is presented; the major aim here being to provide a system design which may be programmed and run on a relatively inexpensive computer installation such as the IBM 1130 system currently in use at Kennedy Van Saun. A summary section is also included, which Provides a general outline guide to the program systems design of equipment which, while quite different from milling system functionally, nevertheless lends itself to the approach used in this paper.

Jan 1, 1969

By A. Bruynesteyn

Many papers 'have been publihed on the role of the bacterium.Thiobacillus ferrooxidans in the oxidation of reduced sulfur compounds, and years of research have established the following environmental factors, which influence biological oxidation. 1. Oxygen is required for the oxidation of reduced sulfur compounds to the sulfate form. Sufficient oxygen. is available from the air, consequently, it is of importance to get the air to the bacteria. 2. The bacteria are active in the pH range 1.4 3.5. Maximum activity occurs at pH 2..0 - 2.8. 3. -In order to allow the bacterial populations to expand, certain essential nutrients must be available. Nitrogen has to be supplied for the production of body protein, and ammonia is the source most readily accepted by the bacteria. Carbon dioxide is the only utilizable source of carbon and the small amounts available in air are the primary source of this element. Small amounts of phosphate, manganese,, potassium,. calcium. and magnesium are also required. These trace minerals are available from the water and host rock in sufficient quantities. 4. Water is required as a carrier for the oxygen carbon dioxide and other nutrients, as-well as a solvent for the metallic sulfates produced. The bacteria are motile and the water allows the bacterial populations to spread:: bacterial activity ceases if the equilibrium relative humidity drops below 100%. 5.-optimum bacterial activity occurs at temperatures of 34 - 35°.C (93 -.95° F). All activity ceases above 45° C. At lower temperatures, activity its dramatically decreased, but there is still a significant amount at 10 - 11° C.- Thiobacillus ferruoxidans has been isolated from a mine with a year round temperature of 3° C. 6. Unpublished results from our laboratory show that biological leach ore oxidation takes place during the rest periods at the same rate as during the wet leaching periods providing there is a film of moisture remaining around the particles. Optimum conditions can be readily achieved in the laboratory, but application of our laboratory knowledge to commercial leaching dumps is riot as simple. Attempts to achieve improved environmental conditions for the bacteria in leaching dumps would require substantial capital investment and careful planning of leaching operations. This paper

Jan 1, 1972

By M. R. Shahan, W. R. Reed, P. Zhang, J. P. Rider

Roof bolter operators may be exposed to high respirable dust concentrations on continuous miner sections with blowing face ventilation when bolting is performed downwind of the continuous miner. One solution to reduce the high respirable dust concentrations is to use a canopy air curtain (CAC) to deliver clean air from a filtered blower fan directly to the bolter operators under the canopies. The influence of CAC installation in the airflow and dust dispersion around the location of the roof bolter operator can be evaluated by using computational fluid dynamics (CFD). This study, performed by the National Institute for Occupational Safety and Health (NIOSH), considers two scenarios: (1) a roof bolting machine in the center of the entry for installation of the fifth row of bolts from the face, and (2) a roof bolting machine positioned close to the face for the installation of the last row of bolts. In both scenarios, the bolting machine is placed in an environment which contains 6.0 mg/m3 of respirable dust and is ventilated by a blowing curtain with 3,000 cfm (1.42 m3/s) of air. This environment is used to simulate the roof bolter machine operating downstream of a continuous mining machine. Two operation positions are simulated at the same bolting location: dual drill heads in the inward position for two inside bolts; and dual drill heads in the outward position for two outside bolts. The influence of the CAC on airflows and dust dispersion is evaluated with the CAC operating at 250 cfm (0.12 m3/s). INTRODUCTION Roof bolting machines are used to drill bolt holes into the roof of an underground mine at specified patterns and to install roof bolts to secure the roof from falling. At times, the roof bolting machine is also used to install rib bolts; however, only the roof bolting operation was considered in this simulation. Though the roof bolting operation drastically improved the safety of miners from roof falls, some roof bolter operators are experiencing health problems associated with respirable dust. Based on recent statistics [1], following a low point in the late 1990s where the prevalence of coal workers’ pneumoconiosis (CWP) in miners with 25 years or more tenure was approximately 5%, CWP now exceeds 10% for miners with 25 years or more of tenure. In central Appalachia (Kentucky, Virginia, West Virginia), 20.6% of long-tenured miners have CWP and 4.5% have progressive massive fibrosis, the most severe form of CWP. CWP, also known as black lung, is an occupational respiratory disease that has no cure and can ultimately be fatal. The only way to prevent the incidence of black lung is to eliminate miners’ exposure to respirable coal mine dust. Current U.S. regulations require that the overall respirable dust concentration to be 1.5 mg/m3 or less for a full-shift sampling if respirable quartz is not present; otherwise, the standard is 10 divided by the percent quartz (not to exceed the 1.5 mg/m3 respirable dust standard) [2, 3].

Jan 1, 2019

By S. Budirsky

J.B. Gwiazda's article deals with an interesting problem that has not been studied thoroughly up to now. Gwiazda has proposed a technical solution that eliminates horizontal load imposed by the supports on the roof. That load is due to a discrepancy between the trajectories of the canopy and the overlying strata. It is true that the improved lemniscate guidance system proposed by Gwiazda could eliminate the horizontal load but, on the other hand, it would represent a higher cost of the supports, and it would complicate the already complicated mechanism of powered supports. That is why we must be convinced that the proposed improvement is actually needed. From that point of view, the following questions should be elucidated. As shown in Fig. 1, the point O travels along the curve a, which produces horizontal load on the roof in the direction of the coal face. As stated by Gwiazda, "such a high load is capable of destroying the roof above the support, causing rock debris to be scattered around the face." The results of our measurements carried out in coal mines of the Czechoslovak part of the Upper Silesian Coal Basin show that the convergence in the modern type of powered supports does not exceed several millimeters (not more than 10) per hour. Similar conclusions were drawn from field measurements performed in the Polish part of the Upper Silesian Coal Basin (see S. Romanowicz and H. Szopka in Proceedings, Scientific and Technical Symposium Simmex '85, Katowice, Poland, pp. 73 -83). The small vertical closure of the supports also induces a small horizontal displacement of the canopy. In addition to this, the transmission of forces between the roof and the canopy is influenced by the layer of debris on it, i.e., the canopy slides without imposing a greater horizontal load on the roof. This was deduced from field measurements of Voest-Alpine F 4/4600 powered supports equipped with rams instead of the common front lemniscate links (denoted as 1 in Fig. 5). In these supports, the pressurizing of the space of piston rod (la in Fig. 5) causes the rams to close, which induces horizontal load on the roof in a direction toward the coal face. After the setting of a support unit, the pressure in the piston rod space was found to drop, frequently to zero, because the small horizontal sliding between the canopy and the debris or inside the debris caused the horizontal reaction from the roof to fall to zero, although the debris were pressurized by vertical setting load. As a consequence, there was no horizontal load imposed by the canopy on the roof. A rise of the horizontal load was recorded only after the passage of the shearer and during lowering of the adjacent units. Thorough information on the results of the afore- mentioned field measurement is given in the paper, "Analysis of the performance of shield powered supports installed in a thick seam," published in Mechanizacja i automatyzacja gornictwa, 1982, No. 12, pp. 38-46. An English translation of the paper is available from the author. We have deduced from our observations that horizontal load imposed by the canopy on the roof in the direction toward the coal face is useful for roof control because it limits the displacement of the immediate roof toward the gob particularly during the rise working. We came to the conclusion that horizontal load on the roof toward the coal face should be induced on purpose. Could Mr. Gwiazda prove with the results of field measurements his contrary opinion? Has the small horizontal displacement of the canopy toward the face actually had an adverse effect on the roof? As shown in Fig. 2, during the setting of a support unit, the canopy imposes a horizontal load on the roof in the direction of the gob. In this case, I share Gwiazda's opinion that the horizontal load could have an adverse effect on the roof. Nevertheless, two important circumstances were neglected - the horizontal compliance of the supports and the interaction of adjacent units. The question of the compliance was analyzed precisely by I. Krumnacker in Gluckauf -Forschungshefle, 1984, NO. 5, pp. 219-223. He found that due to the clearance between the hinge pins and the eyes of the sheild and due to the elasticity of the steel structure,

Jan 1, 1988

By Greg Hodges

Sand-and-gravel aggregates have become the number-one, nonmetallic-mineral resource in the world. Surficial aggregate deposits of economic size are becoming increasingly rare in most parts of Canada. In southern Saskatchewan, this is especially true, and detection and delineation of intertill sand-and-gravel deposits with airborne electromagnetic (EM) surveys have proven very successful. Airborne and ground geophysical surveys detect such deposits by their resistivity contrast relative to the surrounding clay-rich soils. Dighem helicopter-borne electromagnetic surveys map soil variations over a large area quickly and cost effectively, greatly reducing the cost of detecting and mapping deposits compared with traditional methods (air-photo interpretation, ground EM, and drilling.). The multiple-frequency EM system used by Dighem can map variations both horizontally and vertically. Magnetic data collected simultaneously are useful in mapping bedrock geology. Both resistivity and bedrock maps aid in the important task of reducing drilling costs and person-hours in the field. The results of the survey are presented as maps of ground resistivity, which are relatively easy to interpret. These maps are produced in the field at the time of the survey, making quick follow-up of the survey possible. Airborne EM surveys can map the extent and depth of aggregate deposits more effectively than is practical from the ground. Since aggregate deposits can vary tremendously in a very short distance (<300 m) large-area EM maps can show both local area variability and also help develop intertill trends. A test survey for the Saskatchewan Highways and Transportation Department over a 3-km by 5-km area mapped all the known deposits as well as some unknown deposits, subsequently proven by drilling. The test-survey data show that the method not only detected the deposits, but also gave an estimate of the shape (volume) of each of the deposits. Comparison of the data to drill sections shows excellent correlation. Theoretical modelling demonstrates that the multifrequency system can discriminate sand and gravel from bedrock ridges. Since the successful test work, about 725 km2 of ground have been surveyed, resulting in the discovery of four new deposits, which can be used immediately, resulting in significant savings for the Saskatchewan government and taxpayer.

Jan 1, 1999

By R. Wu, R. Howell, J. Dase

Turquoise Ridge is an underground gold mine located in the Potosi Mining District, approximately 64 km northeast of Winnemucca, Nevada. Turquoise Ridge Underground is accessed via two shafts and a system of internal ramps and utilizes underhand drift and fill mining methods with cemented rockfill. The mine also employs mechanical mining as well as sill benching as mining methods. Ground conditions at Turquoise Ridge Underground are poor, and the Rock Mass Rating (RMR) may be less than 20, or very poor, in ore headings. Current production rate is 2,700 tonnes of ore per day. Key challenges in increasing production levels and reducing costs are the development of sufficient stoping areas and the transition from top-cut development to undercut stoping. Completion of the infrastructure development in the North Zone is necessary to achieve and optimize higher production levels. The #3 Shaft project is well underway and is expected to be commissioned in mid. 2022. The shaft will drastically decrease the haulage requirements in the North Zone

Mar 2, 2022

By S. A. Jeric

In-pit crushing and conveying of waste has been utilized in the mining industry for over 30 years. In recent years, innovations in crushing, conveying, and particularly waste and leach stacking technology have sparked a renewed interest in continuous haulage systems for large-scale open pit applications. A review of the advantages/disadvantages and operating techniques of crushers, feeders, conveyors, and stacking systems currently available is made. The paper examines some operations that are currently using large scale continuous haulage systems. Finally, a case study is presented that evaluates the application of a continuous waste haulage system in a large open pit mine in the Western United States, The case study includes a economic comparison with the existing truck haulage system.

Jan 1, 1997

By H. Ban

Triboelectrostatic separation tests were performed on a bench-scale, analytical separator using coal, coal combustion fly ash and mineral samples. Fractions of separated samples were collected and analyzed to characterize the performance of the separation. Particle size distribution and morphological characteristics for these samples were analyzed by optical microscopy, and scanning electron microscopy (SEM). It was found that smaller size fractions of a fly ash sample had better separation than the full sized parent fly ash sample, indicating interference or particle-particle interactions during the separation process. It was also observed experimentally that small kaolin particles attach to the surface of large silica spheres, causing charge neutralization and subsequent low separation efficiency.

Jan 1, 1997

By Theodore H. Budd, Austin M. Cooney

The paper discusses the background and theories of the conditions that led to the settlement of a Lovat TBM mining in an earth pressure balance mode on a recent project in Milwaukee, Wisconsin. The settlement occurred independent of human error and caused the cost of the project to increase 50 percent. The project was mined in the highly congested downtown area in alluvial and estuarine deposits, 7.6 m below the water table with a prescribed contract requirement that precluded dewatering in deference to concern for foundations of adjacent existing buildings.

Jan 1, 1989

By George E. Aikens

Prolonged subzero climatic conditions impose some unique engineering problems for the developer and operator of open-pit mines in the Far North. The remoteness of the job site and the extremely cold, long, dark winters severely tax both man and machine in the quest for the Arctic&apos;s rich mineral wealth. Undoubtedly the singular most troublesome problem for the engineer is Permafrost which underlies about 201o of the land area of the world and about 85% of the state of Alaska. Permafrost has its impact on building construction and mine excavation, while posing a more pervasive threat to the-delicate ecologic balance within the Arctic wilderness. Yet the difficulties associated with mining up North may not be as overwhelming as has been previously supposed. For example, the lowest temperature recorded at Point Barrow is -560F, whereas Montana has recorded -69.7° F.. There are no specially designed machines for mining and construction in the Arctic, and efficient equipment utilization is maintained through proper operation and servicing techniques. However, neither equipment or people can be assumed to function normally at -40°F. Special techniques in drilling, blasting, and ripping are being used to yield economically competitive ores. Overall, a fundamental understanding of the nature of Permafrost will allow the engineer to deal expeditiously with an Arctic mining venture and at the same time to deal fairly with Arctic environment.

Jan 1, 1972

By Dennis Z. Mraz, Maurice B. Dusseault

INTRODUCTION In 1982 and 1983, as part of the mine design program for a New Brunswick potash mine, series of laboratory tests were conducted on potash and salt samples obtained during the mine exploration program. Concurrently, two rock mechanics monitoring programs were initiated in-situ the short term test at site A, and the long term test at site B (figures 1 and 2). SHORT TERM TEST (FIGURE 1) The purpose of this test was to obtain a quick confirmation of laboratory data and comparison of the rock response to excavation with the data available from Saskatchewan potash mines. Instrumentation in the main drift was installed on Day 4 after excavation, and the pressure cells were pressurized on Day 33. The packer type cells in the east crosscut were pressurized on Day 25. Excavation of the west cross-cut was begun on Day 71. This "mine by" test has provided important information required for calibration of laboratory tests, as will be shown later. The test data recorded are shown in a series of diagrams: a. initial room closures, main drift-figure 3; b. convergence graphs, main drift-figure 4; c. stresses recorded, main drift-figures 5 to 8 and, d. stresses recorded, east crosscut - figure15 Three types of instruments were used in this test. In the main drift. Saskatchewan Research Council water type hydraulic inclusions. encapsulated in potash, were used to measure lateral and vertical stresses. In the east crosscut a home-made packer type hydraulic inclusion was used to record radial stresses. The convergence stations consisted of end-grouted bars of reinforcing steel. LONG TERM TEST (FIGURE 2) The purpose of the long term test was to study the steady-state behaviour of a single opening in potash. Site B was placed in a remote area of the mine, well away from any anticipated early mining activities. To assure homogeneity of rock mass, the site was placed within a 30 meter thick vertical limb of a syncline-shaped ore body contained within a 360 metre thick vertical section of salt rocks. It was excavated mechanically as close as possible to the designed square cross-section for the entire length of the room. The square cross- section was chosen in order to achieve a comparable geometry in vertical and horizontal directions; that is, to eliminate any undesired effects of geometry interaction with lithostratigraphy which might have generated non-homogeneous behaviour. The site was extensively instrumented. As in site A, the convergence stations consisted of end-grouted bars of reinforcing steel. However, in order to avoid any measurement inaccuracies which would be associated with the brittle yield zone in the opening walls, bars were placed to the same depth in opposite sides of the opening. This allowed the convergence measurement to be obtained as the absolute convergence between two points, rather than the convergence of a single point with respect to a potentially unstable reference. For stress measurements the Saskatchewan Research Council cells were placed vertically, laterally and radially. Unfortunately, due to cost considerations, it was decided to use a compacted sand, rather than grout, to encapsulate the cells in the boreholes. Due to the extremely small strain rates, only radial ly placed cells could be adequately pressurized. The rest of the cells did not perform adequately, and are currently being replaced.

Jan 1, 1986

By Yoginder P. Chugh

The term "fatigue" in mechanics, is used to refer to reduction in the strength of a material subjected to fluctuating or alternating stresses. Stresses that vary with time are called fluctuating stresses and if during fluctuation the stresses also change sign, they are called alternating stresses. In the field of rock mechanics, the term fatigue (static fatigue) has often been misused to refer to failure of geologic materials in time domain under constant load. To avoid confusion, we use the ten cyclic fatigue here to refer to failure of rock under alternating or fluctuating stresses. Fatigue in metals has been studied for over 100 years. Fatigue properties of geologic materials have, however, received little attention in the past. This is probably because until recently very little was known in regard to the behavior of geologic materials even under static loading. Secondly, suitable equipment for conducting cyclic fatigue experiments was not available until quite recently. A few cyclic fatigue studies have been undertaken on geologic materials to relate it to percussive or rotary drilling mechanisms (e. g. Grover et a11*; Burdine2). The results of these studies were inconclusive due to limited effort. Cyclic fatigue in concrete has been studied more extensively than geologic materials (e.g. Nordby3, Gray et al 4 and Bennett et a15) and mechanisms of fatigue in concrete are better understood than in geologic materials.

Jan 1, 1975

By S. S. Klima, A. L. Mazzella, J. S. Driscoll, T. W. Beck

Previous testing was performed by researchers at the National Institute for Occupational Safety and Health (NIOSH) to improve longwall dust control using underside shield sprays with a longwall directional spray system. This testing provided encouraging results toward respirable dust exposure reductions for longwall personnel, achieving as high as 99% dust reduction at some sampling locations along the longwall personnel walkway. Additional laboratory testing was conducted to test these underside shield sprays in conjunction with a shearer-clearer spray system located on the longwall shearer body. The purpose of this testing was to determine if the underside shield sprays interacted positively or negatively with the shearerclearer sprays. Results from this testing indicate that while the shearerclearer system influences where the respirable dust particles are directed, underside shield sprays can still lower respirable dust exposure for longwall personnel.

Mar 2, 2022