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By Donald Leroux, Ralph Dahlke, Dave Scott, Finch. James A., Cesar O. Gomez

"The efficiency of the flotation process depends on how effectively air is dispersed into small bubbles. Bubble surface area flux - the surface area of bubbles per unit time per unit cross-section area of a cell - is emerging as the parameter to characterize gas dispersion. One of the approaches proposed to measure bubble surface area flux in industrial cells is based on the measurement of two variables: gas velocity and gas holdup, using separate sensors. Plant testing of the gas velocity sensor gave evidence of a series of operational problems which may be necessary to correct before attempting to characterize gas dispersion. Problems such as uneven air distribution within a cell and along a bank, faulty air and slurry valves detected during attempts to redistribute air, and poor control of pulp level and gas flow became evident. Detection of these problems from gas velocity measurements is illustrated.INTRODUCTIONBubble surface area flux is considered a key variable in the optimization of flotation circuit performance (Gorain et al., 1997; 1998). The Mineral Processing Group at McGill University has devised and developed a method for estimating bubble surface area flux in industrial flotation cells (Finch et al., 1999). The method is based on measuring gas holdup and superficial gas velocity using two separate sensors and applying drift flux analysis to estimate bubble size (Dobby et al., 1988; Banisi and Finch, 1994). With bubble size and superficial gas velocity known bubble surface area flux can be calculated.This method was selected by Noranda to characterize gas dispersion in cells as part of a program to model and optimize flotation circuit performance. However, initial testing at Brunswick Mine with the gas velocity sensor provided some unexpected results indicating operational problems and equipment malfunctions that needed to be addressed before systematic measurement of gas dispersion could be initiated.The subject of this communication is to illustrate the detection of these problems from gas velocity measurements. The line 3 Zn Cleaner circuit comprising four stages of Denver DR cells was the main subject of analysis, including the effect of correcting these problems on the metallurgical performance of the Zn 3rd cleaner bank of ten DRl 00 cells."

Jan 1, 2001

By Bern Klein, Randy Blaskovich, Reem Roufail

"Morphology is a tool that is rarely used for mineral breakage mechanism evaluation. Ground particles are typically assessed for their size distribution. They are also visually analyzed using image analysis. However, image analysis is not a comprehensive evaluation of the particle surface texture. It evaluates particle’s size parameters such as area, diameter, and perimeter amongst other features. On the other hand, morphology analysis takes the particle assessment to another level of detail. Morphology analysis evaluates particles’ roundness, elongation and angularity that would indicate the degree of roughness of the particle. According to Roufail and Klein (2009), rougher surfaces are generated due to breakage along grain boundaries – intergranular breakage. Mill operation, particularly mill speed, dictates the dynamics in the mill. Stirred mills are known to break the particles via abrasion under standard operation. However, if the dynamics of the grinding media in the mill are changed, the particles could be more exposed to impact and compression loading that would lead to a different mode of breakage.In this paper, the effect of material properties and mill operating conditions on particle morphology will be studied. Hard non-sulfide versus soft sulfide minerals are compared, namely quartz and galena, respectively. Extreme mill speeds are tested covering the range of 1000 to 2000 rpm for a 4-litre Netzsch (ISA) mill. In addition to particle size distribution, micro-analysis is executed in the form of morphological analysis using a tested manual roughness point counting technique.INTRODUCTIONGrinding in general and stirred milling in particular are processes that are used to break particles to liberate metal-bearing minerals for further separation downstream. The energy required to achieve the target particle size versus maximum possible liberation has been studied intensively and it is usually the breaking point for the grinding system chosen in a process flowsheet. Operating conditions are dictated by the energy consumption. Becker et al. (2001) related different forms of energy such as input, specific, volume/mass specific energies to stress intensities and final product fineness. Other research studies focused on energy input in a stirred mill (Zheng, Harris and Somasundaran, 1996)."

Jan 1, 2011

By Karl J. C. Harries

"12.1. NO DEPRECIATION/GAAPAll calculations and computations relating to the Royalty shall be carried out in accordance with generally accepted accounting principles consistently applied to the extent that such principles are not inconsistent with the provisions of this Schedule and the agreement attached hereto, it being specifically agreed that nothing herein contained shall permit, or be construed to permit, the Operator to deduct any amount for depletion, depreciation, amortization or any deduction that represents a non-cash outlay.Comment: In cases like net profit royalties where recoupment of prior expenditures is permitted, care should be taken to avoid any implication that depreciation may also be taken. It is only logical and equitable that Property Owners should not be permitted an apparent ability to “double dip” with respect to deductions. A provision like this example should accomplish the task. It will be noted that the example specifically contemplates that the negotiated arrangements will prevail over any requirements of GAAP. Accordingly, if the parties agree to an unusual formula for recoupment, it will not be set aside to accommodate GAAP requirements. Under GAAP, revenues and expenditures are accounted for on an accrual basis. In addition, it specifically prohibits the taking of non-cash deductions, which is in keeping with the concept of recoupment.Although in some ways the example states the obvious and could be considered redundant, its presence, especially in provisions contemplating recoupment, makes it clear to the financial people that there may well be some variations from normal practices dictated by GAAP, while at the same time confirming the availability of GAAP to fill any voids.The accounting profession often makes the caveat that application of GAAP is an “art”, not a “science”. GAAP do not provide a cure-all and can create problems that will have to be addressed. For example, GAAP contemplate that asset costs are to be reduced by investment tax credits, which can cause a problem for a payor with more than one mine."

Jan 1, 2003

By Sam S. Taylor

"INTRODUCTION This report deals with a comparatively simple application of some of the engineering principles involved in the evaluation, installation, and operation of air- or gas-injection projects and well-clean-out and repair methods to increase the producing rates of oil wells in partly depleted pools during the war. The methods suggested for developing gas-injection projects take into consideration that in general no new wells will be drilled because of wartime restrictions of equipment and manpower and that only existing wells and second-hand machinery will be used. Because air will be employed as the injection medium in secondary-recovery operations where natural gas is scarce and expensive, the disadvantages and hazards accompanying, its use are discussed. Engineering techniques recognized as best modern practice are discussed in relation to the effect of simple air-injection development of properties on postwar operations and Probable ultimate recovery of oil. The report is an introduction to where, when, why, and how an air-injection project should be installed and operated; it is not intended to be an engineering manual for technical guidance in the selection, development, and operation of simulative methods of oil recovery.The report is intended mainly for these thousands of operators in the Appalachian region owning a few wells prodding small quantities or oil daily. Many such operators are anxious to increase their production rates by simulative means and to rehabilitate their wells so that they will produce more oil to help win the war but, in general, are unfamiliar with secondary-recovery operations and cannot afford to hire technical assistance."

Sep 1, 1944

By Esteban Bravo

El presente señala la utilidad del último software y equipos desarrollados como herramientas que permiten analizar, monitorear y reparar los problemas que se presenten en el funcionamiento de motores diesel, además de disminuir los costos para su mantenimiento.

Aug 25, 2002

By Dan Witkowsky

Beginning on June 11, 2007, as many as 36, kindergarten-to-grade-12 (K-12) teachers will participate in a program designed to educate them all about the mining industry. The 39th Annual A Total Concept of the Mining Industry – All About Mining, will be conducted by the Colorado Mining Association Education Foundation, Inc. (CMAEF) and the Office of Special Programs and Continuing Education (SPACE) at the Colorado School of Mines. This flagship program includes four intensive weeks at the Colorado School of Mines. During that time, more than 75 volunteer lecturers will “educate the educators” about mining and its importance to the United States and the world. During the learning process associated with obtaining a basic understanding of mining and all its aspects, the teachers will be hosted by hundreds of other industry professionals at 10 Colorado mining operations. Also visited will be a government earthquake center, a museum of mining and industry, an earth mechanics laboratory, a metallurgical research center, a metallurgical concentrator, an electric power plant and a steel mill. Questions before, during and after visits will be answered by another select group of volunteers who will travel with the teachers to the various sites.

Jan 1, 2007

By R. Jolicoeur, J. F. Jackson, M. A. Green

"The design, construction and commissioning of Kiena Gold Mines Limited's new mill was completed in 15 months ending in September 1984. Rated at 1250 tonnes per day the mill incorporates the latest innovative technology such as semi-autogenous grinding, carbon in pulp, pressure stripping and induction furnace refining. The mill is housed in a pre-engineered building with the leach tanks and thickeners located outdoors in spite of the intense winter cold. 1.0 INTRODUCTION AND HISTORYThe operations or Kiena Gold Mines Limited are located in Dubw1sson Township, approximately 10 Km west of Val d'Or, in the Abitibi region northwestern Quebec. Comprised of 59 mining claims covering 1214 hectares, a large portion of the mining property is overlain by the waters of Lac de Montigny. Sometime between 1911 and 1914 Barney Parker discovered gold in a shear zone on an island in Lac de Montigny that now bears his name. The first shaft the Parker Shaft, was sunk in 1936 from the island to a depth of 136 meters but owing to the known veins being of limited extent and the onset of the Second World War operations were terminated in 1940. In the early l960 1 s exploration drilling indicated an orebody of 4,500.000 tonnes at 6.3 grams of gold per tonne. A causeway was built to link the island to the mainland in 1963 and a new 3 compartment shaft was sunk to 403 metres. The orebody was further delineated and the ground conditions within the orebody and surrounds were evaluated.At the end of 1965 the property was placed on a care and maintenance basis as a mining operation would be marginal with gold selling at $35 per ounce."

Jan 1, 1986

By K. K. Murray, D. G. Gelderland

"The pressure oxidation autoclave at the Goldcorp’s Red Lake Gold Mines (RLGM) was commissioned in 1991. Since commissioning, the circuit has been well maintained and its capacity increased to mechanical and gaseous oxygen limitations. With advances in available technology, opportunities to produce more sulphide concentrate and a changing business environment, an optimization project has been initiated at RLGM. A multi-phase approach has been developed to optimize both the operations and economics of the circuit. This paper describes the history and future of the autoclave circuit at RLGM.AcknowledmentsWe would like to thank the operations and maintenance staff at Red Lake Gold Mines for their support and openness of mind to enact changes to enhance the operation. We would also like to acknowledge the members of the integrated team from Red Lake maintence, metallurgy, operations and corporate technical services that did the hard work to push past the status quo in order to advance productivity.OpportunityThe Red Lake Gold Mines (RLGM) pressure oxidation (POx) circuit has been in operation for over 25 years processing the high sulphide content gold bearing minerals. Increased sulphide concentrate production from improved flotation recovery and increasing gold sulphide association at depth has led to the POx circuit becoming a throughput bottleneck. The opportunity exists to process increased tonnages of sulphide concentrates and increase gold production. In order to realize this value, it will be necessary to increase the throughput capacity of the POx circuit.BackgroundThe POx autoclave at the RLGM, commissioned in 1991, was Canada’s first gold autoclave. It was installed to replace the two-stage fluid bed roaster that was built when the Campbell mine and mill were constructed in the late Forties. The circuit was originally designed to process 12.5 t/d sulphide sulphur in about 50 t/d of Campbell flotation concentrate. Following the merger of the Campbell and Red Lake Mines in 2006, the POx circuit started processing flotation concentrate from both Campbell and Red Lake Mills. In recent years, the circuit has been processing about 18 t/d sulphide sulphur in 75-85 t/d flotation concentrate."

Jan 1, 2017

According to the data provided by the most recent European Survey on Working Conditions, roughly 25 per cent of the European working population is exposed to mechanical vibrations for no less than one quarter of the work shift duration, while around ten per cent are exposed for the entire work shift. The occupational exposure to whole-body vibration (WBV), in particular, represents a major health risk in mining, quarrying and civil excavation activities. In accordance with European Directive 2002/44/EC, the latest version of the Italian law on physical risks has recently confirmed the possibility of using relevant literature data on vibration magnitude in order to evaluate personal occupational exposure (vibration database or data provided by the manufacturer). Still the alternative option, based on field measurements, represents the most appropriated method of risk assessment, as it accounts for the actual operating condition at the workplace; actual operator and vehicle under investigation and specific working cycle. The article discusses the vibration measurements taken on a number of heavy machinery (excavators, loaders, trucks, dumpers, etc) employed for talc extraction in a mine located in Sardinia and the resulting personal exposure for the drivers. The assessment was carried out in accordance with the specifications of ISO 2631-1 and EN 14253.

Dec 6, 2010

By Darelle T. Janse van Rensburg

Some of the more recent developments in Paint Technology are solvent free materials. These coatings have mainly been formulated to overcome the negative attributes of solvent-based coatings, i.e. environmental, safety and health risks, potential for solvent entrapment and osmotic blistering, as well as the formation of micro-pores during the curing process. Two solvent free liquid epoxy coatings have been used extensively on power generation plant. However, very little is known regarding their long-term performance under different exposure conditions, as well as whether these coatings actually perform better than their solvent-borne counterparts. In addition, solvent free materials are generally used where outage periods are restricted and coatings need to be applied within a very short period. Though these materials have reportedly much shorter curing times than other conventional solvent-borne coatings, little is known regarding their limits with respect to maximum film thicknesses and being put into service while still being wet/partially uncured. The latter has become common practice at many power stations in the past two years or so. In addition, the application and curing methods of solvent free materials are different to that of solvent-borne materials, and may require equipment and application process changes. This paper covers the application and performance properties of solvent free coatings in comparison to solvent-borne materials primarily intended for immersion service. Numerous coatings were evaluated under immersed static and cyclic hydrostatic pressures. Other tests included short curing / early immersion tests, dry-to-touch and dry-through curing times, adhesion tests, surface tolerance tests, etc. The results show that the solvent free materials have clear benefits with respect to safety, health, environmental and long-term performance, but will be more difficult to apply compared to solvent-borne materials.

Jan 1, 2006

By Koji Matsubara, Yoshiaki Iguchi, Shoji Hayashi

Iron ore particles of a limonite iron ore were reduced completely with H2 at 1023K to 1273K in a fluidized bed. Then, at 973K, the formed iron was exposed to HrH2S mixtures (sulfur activity, as=0.5) for 3.6ks and carbidized with CO-H2-H2S· mixtures at 0.1 MPa. During the carbidization, the particles of about 150mg were sampled at every 600s interval. The sampled particles were analyzed by XRD and chemical analysis for C and S to evaluate the content of Fe3C, Fe5C2, Fe and free carbon. The reaction extent is defined as fo=Xfc3C +xFc5c2; x is the molar fraction of Fe in Fe3C. The carbidization curves can be fitted very well to -ln(l-f0)=g(pb T)t; g(p; T) is the carbidization rate, i.e. the carburization rate on the pore surface of reduced iron. The rate is found to be nearly proportional to the specific surface area of reduced iron, a P 0 , which decreases with increasing the reduction temperature. The value of a P 0 does not change by the carbidization and the stability of the iron carbide product in the atmosphere increases with the temperature.

Jan 1, 2000

By R. G. Knickerbocker, T. E. Evans, D. R. Torgeson

"INTRODUCTION Sponge iron is a product resulting from the reduction of an iron oxide at such a low temperature that fusion does not occur, and the reduced particles retain substantially the same shape as the original ore. The removal of oxygen in the reduction process leaves the metal porous and reactive. Sponge iron may be compared in general to a chemically precipitated substance insofar as reactive properties are concerned. The high specific surface and the orientation of metallic structure are factors which probably contribute to the reactive properties of sponge iron.The term ""gaseous reduction,"" as applied to iron ores, required clarification. Strong evidence exists, for example, that ore is partly reduced to sponge iron by carbon monoxide in the blast furnace at temperatures around 800° C. at a point that may be as high as 30 feet above the tuyores. In 1923 and 1924, Sims and Wood attempted to reduce iron oxide with carbon in an Arsem vacuum furnace at 980° C. These investigators found that only 6 percent of the iron was reduced to metal when the iron oxide-carbon mixture was heated for 1 hour under evacuated conditions, whereas at atmospheric pressure 70 percent of the iron was metallized. Their results indicate that the process of iron-ore reduction at temperatures below the melting point of the ore may proceed largely, if not entirely, by the action of reducing gases even when the reducing agent is solid carbon. Therefore, the term ""gaseous reduction,"" as used heroin, is defined as a process in which iron ore is brought into intimate contact with a reducing gas produced in separate-equipment from the reduction chamber itself.A large amount of pilot-plant development on gaseous reduction of iron ores has been carried out by the Bureau of Mines at the Boulder Experiment Station and had as its objective the reduction of fine iron ore by means of producer gas. The use of use gas was prompted by two considerations: First, the possible utilization of large reserves of Western noncoking bituminous coals and lignites contiguous to iron-ore drewwing; and second, an investigation of the results that might be achieved in the pilot-plant gaseous reduction of fine iron ores by means of a relatively reducing gas. The results obtained, it was felt, would be of considerable value in indicating the direction which gaseous reduction experimentation must take for the development of a commercially practicable and economic process for the production of sponge iron."

Dec 1, 1946

By Eric L. Trist

The objective of this contract was to review the results of the Rushton Mining experiment in work organization and design, to explore the extension of knowledge gained from Rushton to other underground coal mines, and to conduct a search for a potential mine site for a demonstration project. The primary focus of the contract was on a search process to provide the research team with the opportunity to evaluate the different potential experimental sites, in order to select one or more with the highest potential for success. This search process also provides the various levels of union and company officials the opportunity to fully understand the context of the research before making a decision on whether to participate. While the search project failed in its attempt to locate a specific mine site, the research team believes that this is not a rejection of the actual project but rather extreme caution because of the uncertainty within the UMWA.

Jan 1, 1978

By A. Yu. Lein, V. V. Maslennikov, S. P. Maslennikova, I. Y. u. Melekestseva, Yu. A. Bogdanov

Tellurium is a high-tech and also toxic element. This element shows sufficient contents in Fe-Mn crusts and nodules in the modern ocean to be involved in future industrial processes [Hein et al., 2003]. Tellurium minerals and contents are not well recorded in modern and ancient black smoker systems. Tellurides are rarely found in sulfides from the modern oceans [Iizasa et al. 1992; Maslennikov et al., 2010]. The previous common opinion that tellurium is scarce in active seafloor hydrothermal systems can be revised due to the recent discovery of abundant tellurides in chimneys from Brothers Volcano vent site [Berkenbosch et al., 2012]. We found abundant tellurobismuthite, hessite, and native tellurium in chimneys from Su Su Knoll vents sites (West Pacific). So, tellurides can be found in some chimneys but absent in others. The causes of this are poorly understood. These conflicting data create numerous questions and require an explanation. The problem can be resolved by research at different scales including analysis of relevant genetic features of host sequences, systematic textural and paragenetic studies of different types of chimneys, and their rare mineral assemblages. Paragenetic models, compositional analyses and ranges of tellurium-bearing minerals and the physicochemical interpretation of chimney diversity in different types of VMS deposits are the main subjects of our research. The data on tellurides in chimneys from ancient VMS deposits should also be useful to resolve this problem.

Sep 1, 2014

At the Prospectors and Developers Annual Convention (PDAC) in Toronto, Canada mining and exploration companies of all sizes were on hand to discuss the year that was and those that will be. The following is a look at some of the companies with Canadian operations that were on hand for PDAC 2009. Iamgold Corporation is a leading mid-tier gold mining company producing approximately 31 t (1 million oz) of gold from seven mines on three continents. With record revenues of $870 million ? up 28 percent when compared to 2007 ? the company is focused on growth with a target to reach 56 t (1.8 million oz) gold production by 2012. During 2008, the company acquired the Essakane project in West Africa. The project is fully permitted, under construction and will contribute more than 9.3 t (300,000 oz) of lower cost production by late 2008. Iamgold increased its reserves by 55 percent, to 385 t (12.4 million oz) and its resources in-creased by 16 percent to 821 t (26.4 million oz) in 2008. Going forward, Iamgold has three areas of focus ? West Africa, Guyana Shield and Quebec ? with seven gold operations, five advanced projects and the Niobec niobium mine included. The Rosebel Mine in Suriname is Iamgold?s fl agship property. With measured and indicated resources of 300 t (9.6 million oz), it accounts for 30 percent of Iamgold?s production. Production there was up 20 percent compared with 2007 and further production increases are expected in 2009 and 2010. Mill expansion and optimization increased throughput from 8.9 Mt/a (9.8 million st) to 10 Mt/a (11 million stpy). In West Africa, Iamgold has joint ventures at Sadiola in Mali; Tarkwa in Ghana; Yatela in Mali and Daman in Ghana. Iamgold also has 100 percent ownership of the Mupane gold mine in Botswana and the Doyon gold mine in Quebec, Canada. Also in Quebec, Iamgold has 100 per-cent ownership of the Niobec niobium mine in Quebec. Niobium is used in high strength specialty steels.

Jan 1, 2009

By Kadri Dagdelen

Design of the ultimate pit limit to direct long range mine planning has been a celebrated problem in the mining industry, and in mining academia, since 1965. Although many papers have been presented on this topic, even today, there is not a single solution technique which is widely accepted and considered universally best. Many philosophical differences exist among the pit planners concerning the use of different methods and it appears that resistance is very strong towards accepting other techniques if you are a believer in one. Whatever the case might be, the pit parameterization technique for the ultimate pit limit design is the latest and takes a different approach than its predecessors. There are already a number of papers which discuss the concepts involved (Francois-Bongarcon, 1976; 1978; 1980; 1981); however, the aim of this paper is to fill in some of the gaps which are thought to be missing in the previous discussions and, in addition, to present the recent research done on the subject at the Centre de Geostatistique de l?Ecole de Mines de Paris in Fontainbleau, France. This paper is divided into two parts. The first part will discuss practical aspects and interpretations of pit parameterization concepts with- out using mathematical or theoretical arguments; the reader who is interested in the theory should refer to Francois-Bongarcon (1978). The second part will present an approach to obtain a complete double parameterization of reserves using an inexpensive (computer costs) single parameterization algorithm. A case study of this approach is also included.

Jan 1, 1982

By Ron Millions, J. A. Folinsbee, Ishwinder Grewal, Michael Fullam, Don Strickland, Tony Y. Chong

"Since milling began in 1912, the Dome mill, now part of the Porcupine Joint Venture (PJV), has been expanded several times, the most recent increasing the milling rate from 3,500 to 11,500 tonnes per day. Dome uses conventional crushing and grinding followed by gravity concentration to recover free milling gold. A cyanidation/CIP process recovers the remaining gold in the gravity tails.Over the past few years, continuous gravity improvements have increased the gravity recovery from 20% to nearly 50% of the plant feed gold. This paper describes some of the factors that have contributed to this dramatic increase, and suggests how gravity recovery can be further improved. Gravity circuit availability has been improved to >98% with the implementation of a preventative maintenance program. More Knelson concentrators have been added to the circuit, and in 2002, an Acacia Intensive Leach Reactor was installed to replace the shaking table. In 2003, the entire gravity circuit was audited to evaluate and quantify the circuit performance. The metallurgical and mechanical operating conditions of the gravity circuit are now well understood, and areas for further improvement are well defined.INTRODUCTIONThe Porcupine Joint Venture was formed in 2002 between Placer Dome Inc. and Kinross Gold Corporation. One of the goals of the JV was to use the milling capacity of the Dome mill to process ore from Placer Dome and Kinross mines in the Timmins Camp. The PJV Dome Mill utilizes gravity concentration, cyanide leaching and carbon in pulp gold circuits to recover gold. Gravity recovery has been used in some form at the Dome Mill for most of its existence, first using conventional jigs, these being replaced in 1993 by two Knelson Concentrators, one for each of the two grinding circuits in the Dome mill. Over the years more concentrators have been added to improve the gravity recovery, most recently in 2002 for a current total of five. Also in 2002, an Acacia Intensive Leach Reactor was added to process the Knelson concentrate, replacing the shaking table."

Jan 1, 2004

By R. L. Merek

There were 63 fatalities in the California petroleum industry in 1929, the largest number in any year since 1923 and an increase of 34.0 per cent over 1928, when 47 men lost their lives in the drilling, producing, manufacturing, and marketing divisions of the industry. It will be observed from the accompanying chart that after following a consistent decline for 4 years, the fatality curve turned upward in 1923 and advanced sharply in 1929. Although this increase in fatalities coincided with a period of intensive development it tends to indicate some laxness in the industry during a period of increased hazards. Intensive drilling campaigns are usually started hurriedly and conducted with a great demand for speed, and the result is that accident-prevention work is too often relegated to a position of minor importance.

Jan 1, 1930

By R. L. Marek

There were 63 fatalities in the California petroleum industry in 1929, the largest number in any year since 1923 and an increase of 34.0 per cent over 1928, when 47 men lost their lives in the drilling, producing, manufacturing, and marketing divisions of the industry. It will be observed from the accompanying chart that after following a consistent decline for 4 years, the fatality curve turned upward in 1923 and advanced sharply in 1929. Although this increase in fatalitics coincided with a period of intensive development it tends to indicate some laxness in the industry during a period of increased hazards. Intensive drilling campaigns are usually started hurriedly and conducted with a great demand for speed, and the result is that accident-prevention work is too often relegated to a position of minor importance. [ ]

Jan 1, 1930

By V. V. Nazimko

Abandoned coal mines cause subsidence and structural damages. Shallow abandoned mines induce the most severe and harmful damages. In addition, they produce time-dependent subsidence which is difficult to predict. Backfilling of underground cavities with waste materials have been used to prevent the time-dependent subsidence or to mitigate its effect. However, this procedure is expensive. A new drill and blast technique has recently been proposed to prevent surface damage from time¬dependent subsidence over abandoned mines. It utilizes the principle that blasting in the caved rock and roof in the vicinity of a cavity will dilate the ground and create a self-supporting effect owing to increase in the volume. Physical modeling has demonstrated that artificial dilation of caved rock using the drill & blast technique creates positive effects due to the following sequence of events: the dilated rock creates a supporting effect for the suspended rock strata and reduces its span which decelerates 3.4 times the process of caving. The roof span is reduced by the next caved layer, which causes the hole boundaries to incline to each other. This effect converts the process of caving from a developing mode to a reduction mode. Finally, the sinkhole zone assumes a triangular shape with a negative angle of draw 64-700 in contrast to a rectangular shape of the chimney zone for natural caving. Vertical dimension of the triangular zone is 3.87 times of the room height. Final surface subsidence decreases at least 2.09 times; displacement 1.31 times, slope 2 27 times; curvature 3.42 times, horizontal strain 1 21 times in comparison to natural caving of the ground over an abandoned mine.

Jan 1, 1999