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By Tatiana ?. Sedysheva, Vladimir V. Ivanov, Michail E. Melnikov, Irina A. Pulyaeva

"INTRODUCTIONHydrogenetic Fe-Mn crusts are ubiquitous in the ocean basins and play an important role in marine mineral-deposit research because of their widespread occurrence and high concentrations of valuable and rare metals. Directed research, which started in the last quarter of the 20th century, has provided significant results, with substantial amounts of data produced on Fe-Mn crusts structure, composition, and distribution in the global ocean [3, 4 - 8]. Now, commercial interests gain more and more attention. Mining systems are being developed which involve fragmentation of the crusts and their separation from the substrate. The effectiveness of such activities greatly depends on physico-mechanical characteristics of the crusts and rocks on which they form. This determines the importance of the engineering geological study of the objects.This article comprises the results of the engineering geological studies of the crusts samples (72 samples) and their underlying rock substrates (75 samples), which were carried out during the research cruises 6-06, 6-07, 6-08, 6-13 (2006-2013) on the Magellan Seamounts guyots in the Western part of the Pacific Ocean by the specialists of the State Scientific Centre Yuzhmorgeologia [10 - 13, 19, 20]. The authors of the article directly participated in the studies mentioned above.MethodsEngineering geological studies were carried out on board of the research vessel Gelendzhik and in the laboratories of NPA «Sevmorgeologiya». The studies involved the determination of the following parameters:"

Jan 1, 2017

By Linda L. Chasko, Larry D. Stowinsky, Ronald S. Conti

Mine operators often rely on mine rescue teams to save lives during an underground emergency such as an underground fire, explosion or roof fall. It is extremely important that team members are provided with adequate exploration equipment and that training simulations are conducted in a realistic manner. A series of mine rescue training exercises was developed, conducted and evaluated by the National Institute for Occupational Safety and Health (NIOSH) in cooperation with the Pennsylvania Department of Environmental Protection, Bureau of Deep Mine Safety. The exercises were conducted at NIOSH’s Lake Lynn Laboratory during 1995 to 1998 and resulted in improved technology and training for mine rescue teams. For example, existing technologies were identified to help rescue teams during exploration. These included chemical light sticks to identify team members and mark crosscuts and mine materials, strobe lights for mapping out escape ways, and a helmet mounted thermal imaging system to see through smoke. A hands-free communication system showed potential for enhanced communications between team members and the fresh air base. A new high-visibility team lifeline that allows for flexibility of movement between team members was developed. A positive-pressure inflatable escape device (IED) was used to isolate the “hazardous” environment from fresh air and allow rescue team members to traverse through. An inflatable feed-tube partition that can rapidly block large openings such as underground passageways and simultaneously provide a feed-tube for high-expansion foam generators was also deployed for several simulations. During the simulations, mine rescue team members donned self-contained breathing apparatuses (SCBA) and traversed more than 305-m of mine passageways filled with nontoxic smoke. Visibility ranged from 0.3 to 0.9-m. In one area of the mine, a kerosene heater was used to simulate a fire and reduce the oxygen concentration. In another area, a 1.5 pct methane zone was established. The team members searched for "victims,” mapped the passageways, built temporary stoppings and ventilated the smoke-filled entries. The teams indicated that the simulations were challenging and very informative.

By T. C. Moore

This report describes the feasibility test of an electromagnetic method for locating boreholes, with or without casing, that have been drilled in conjunction with mining operations but whose location with respect to the tunnel is not precisely known. The first tests were conducted with the cooperation of the Kerr-McGee Corporation, Church Rock Mining Operations, New Mexico, in September 1977. These tests demonstrated that accuracies of better than ±5% of range and ±1° of bearing can be achieved with a simple system and setups. Subsequent tests, in January 1978, on a horizontally drilled pipe line river crossing application, by Titan Contractors of Sacramento, California, demonstrated that accuracies of better than one-half percent of range and a few tenths of one degree of bearing can be achieved by using refined techniques. The demonstration tests were done at ranges on the order of 100 to 200 feet but the method is capable of working at much greater distances.

Jan 1, 1978

By Hans Korfmacher

Product take-back regulations implemented in Europe have presented significant challenges to the consumer electronic product and battery industries. Initially companies established single compliance organizations within individual Member States. These programs met business needs but were inefficient and costly. They were protected from pressures of marketplace competition and could not leverage economies of scale. In order to address these problems P&G, Hewlett Packard, Sony and Electrolux conceived a pan-European compliance organization to collect waste electronic equipment Europe-wide. This organization, called the European Recycling Platform (ERP), operates in competition with existing national compliance systems. Since 2005 ERP has collected 800,000+ tons of waste electronic products and delivered millions of dollars in cost savings. This presentation reviews the steps needed to establish successful competitive collection organizations that provide sustainable recycling at the lowest cost.

Jan 1, 2010

By H. L. Hopkins, OHIO, L. W. Kemph, CLEVEL AND, E. V. Ivanso

A balanced system of internal stress is set up in any metallic structure by plastic deformation below the annealing temperature. The internaI stress induced by cold rolling or other fabricating processes is generally recognized and its magnitude is known to be, within certain limits, a function of the degree of cold deformation. The plastic deformation that may accompany rapid cooling from elevated temperatures may not materially change the form of the product. The internal stresses so induced are not, therefore, so evident and nonrecognition of their presence has at times led to engineering failures. The heat treatment of aluminum alloys is a relatively new art and little information is available regarding the magnitude of stresses induced during the commercial heat treatment of aluminum alloy products. As the industrial use of aluminum increases, it is inevitable that products of increasingly large volume will be required. It has become necessary in the present commercial utilization of aluminum to heat-treat castings and forgings weighing hundreds of pounds. One of the factors governing the magnitude of internal stresses arising from rapid cooling from elevated temperatures is that of the size of the structure being treated. Some of the other factors are: cooling rate, elastic properties of the alloy, thermal expansivity, thermal conductivity, and the presence or absence of phase changes. Practically all aluminum alloys have a high coefficient of thermal expansion and some are capable of developing relatively high elastic limits. On the other hand, all commercial aluminum alloys have relatively high thermal conductivities, no invariant phase changes, and the quenching temperatures are comparatively low. In the absence of invariant phase changes involving change in the type of crystallographic lattice, the fundamental basis for the development of internal stress

Jan 1, 1934

By Thomas Donnelly

Introduction THE Province of San Cristobal is situated on the south side of the island of Santo Domingo about 25 miles west of Santo Domingo city, the capital of the republic. The copper mineralization is found about 1.-CAMP BUCARO. THE TOP OF THE RIDGE IN THE BACKGROUND MARKS THE CONTACT OF THE LIMESTONE AND TUFFS. S miles north of the town of San Cristobal, in the section known as Bucaro Hill; in San Francisco Hill; on the Nigua River; and on the Jaina (Liver. The district is reached by automobile from Santo Domingo city over an excellent road for 25 miles to San Cristobal, and then, by horse-back 6 or 8 miles up the Nigua River to what is locally known as "Camp

Jan 8, 1915

By Craig C. Hustwit

A pilot-scale treatment study was conducted on a copper-zinc bearing metal mine drainage using a pipeline treatment system called the In-Line System (ILS). The objective of this U.S. Bureau of Mines study was to determine whether the ILS could be extended from the treatment of coal mine drainages to the treatment of metal mine drainages. Hydrated lime (Ca(OH)2), quick lime (CaO), and caustic soda (NaOH) were used to neutralize the drainage. A novel reagent slurry of Ca(OH)2 and type C fly ash was also evaluated. Except for Ca(OH)2-fly ash slurry, treatment performance was evaluated for all reagents at pH values of 7,8,9, and 10. The Ca(OH)2-fly ash slurry was evaluated at a pH of 10. All reagents tested neutralized the metal mine drainage and substantially reduced the dissolved metal concentrations. It was concluded that the ILS could be useful in the treatment of metal mine drainages.

Jan 1, 2010

By G. R. Lane

A large opencast gold mining company in Africa had just completed a feasibility study for the expansion of the operations. A traditional net present value project valuation methodology had been used that showed a very positive net present value (NPV). The project team had conducted a qualitative risk assessment that identified and logged all potential project risks and had subjectively incorporated ?risk? via the discount rate and other assumption contingencies around gold price expectations, operating parameters etc. Management requested that an independent quantitative risk modelling approach be adopted to obtain a better understanding of the impact of risk on the overall project valuation and confidence level in the final valuation. A detailed project valuation model was configured in the Carbon Modelling Technology and the stochastic modelling module used to perform the Monte Carlo simulations. Analysis of historical operational performance data relating to actual achievements versus planned and budget determined the historical variability of the underlying parameters as well as variance to budget. This was done at a detailed level for mining rates and costs, processing rate, costs and recovery, and other operational efficiency measures. External market assumptions relating to gold price, exchange rate, and inflation were modelled and the dependency between them modelled using a copula. This case study will demonstrate the approach taken to building and populating the quantitative risk model and the overall results of the Monte Carlo simulation. The final valuation demonstrated that the project had a 44 percent probability of an NPV less than zero i.e. 44 percent chance of project finance loss.

Jan 1, 2012

The U.S. Bureau of Mines conducted a laboratory study to determine what effect use of water-jet-assisted cutting has on frictional-ignition suppression. A single bit with a steel tip, installed on a rotating drum, repeatedly made 22-in-long cuts in a block of Berea sandstone. The drum was operated in an enclosure that contained an explosive methane-air mixture. High-pressure front-mounted water jets operating at 2,000 to 5,000 psig and low-pressure rear-mounted sprays operating at 80 psig were used; the number of ignitions that occurred with each type of spray was compared. The rear-mounted spray was more effective for preventing frictional ignitions than the front-mounted water jet.

Jan 1, 1989

By R. Heikkilä

Today road construction sites utilize more and more information modeling in design phases as well as model based 3-D machine control systems in site operations. For main contractor, the management and control of all the site operations is a demanding task including also many challenges created by continuously developing new technology. In the paper, the main requirements for successful dynamic site management are introduced. The dynamic management means real-time possibilities for information acquiring, transfer and further utilization of the information in the management. An integration model to expand the current way of management and the utilization of present 3-D machine control systems is introduced. Different practical test results using two new different dynamic management systems are presented and evaluated. The first experiments and the results have been provided using the prototype system developed in a research project called DigiINFRA by the University of Oulu and Technical Research Center of Finland. Also, there have been tested a new commercial management system developed recently in Finland. In the conclusion, an expectation for the next generation for more dynamic road construction management methods is concluded.

Aug 1, 2013

By G. P. Gu

The in-service 90/10 cupro-nickel tubes in a water-chiller system suffered from severe corrosion damage during their relatively short service life causing unexpected down time. In addition to downtime, the environmental risk associated with losing refrigerant was also a concern that initiated this investigation, Microstructural investigation using SEM and electron microprobe indicated that pitting corrosion had resulted in local nickel depletion, During the corrosion process, copper appeared to have re-deposited around the corrosion pits accelerating the local corrosion.

Jan 1, 2005

By B. Oladipo, E. Govender-Opitz, T. V. Ojumu

Bioleaching, one of the several important processes of biohydrometallurgy is an accepted technique for the extraction of desired metals from sulphide ores. Although the mechanism is well understood, the slow metal extraction rate due to passivating layer and ferric ion precipitation, especially in a typical chalcopyrite leaching, impact negatively on the overall efficiency of the process. Iron precipitates are common in many biohydrometallurgical operations and these precipitates represent the exit route for undesired iron, alkali ions or sulphate ion from the processing circuit. While there have been reports on approaches to slow the formation of these precipitates by manipulation of various operating conditions such as pH, redox potential and temperature, the precipitates become highly significant over the long term in the continuous operation of bioleaching and may render heap impermeable. Although there is evidence supporting the nature of the passivation to be precipitates of iron, their scavenging mode of reducing extraction efficiency is still not well understood. This paper thus discusses iron precipitation in biohydrometallurgical processes, including its formation and significance on bioleach processes. The paper also details the associated passivating species identified with heap bioleaching of sulphide minerals and provides some insight into sorption mechanism that limits metal recovery in a typical bioleach operation. Keywords: Iron precipitation, bioleaching, chalcopyrite, passivation, jarosite, metal sorption

Jan 1, 2020

By N. W. Hendry

ABSTRACT Exploration by geophysical methods and diamond drilling of an occurrence of chrysotile asbestos, located ten miles east of Matheson, Ontario, was commenced on March 25th, 1949, by the Canadian Johns-Manville Company, Limited. The asbestos is associated with a narrow sill-like body of basic and ultrabasic rocks which strikes northwesterly across portions of Munro and Beatty townships. To date, asbestos zones of commercial interest, many hundreds of feet in length, width, and depth, have been outlined by diamond drilling along a 2-mile length of serpentine. The fractures occupied by the asbestos veins are closely associated with the regional faulting in the area. The mining of the first occurrence, or A orebody, will be by open-pit methods. Milling will commence at a rate of 50 tons an hour. INTRODUCTION OCCURRENCES of chrysotile asbestos in Munro township have been known at least since 1914 and references to them appear in reports published by the Ontario Department of Mines in 1915 (1) and 1919 (2). J. G. Ross (3) in his excellent publication on Chrysotile Asbestos in Canada, mentions an occurrence in Munro township. The area was first mapped in detail by J. Satterly, of the Ontario Department of Mines, in 1944, and brief mention is made of chrysotile asbestos in Satterly's preliminary report (4), which was published the following year.

Jan 1, 1951

By L B. Sukla, V N. Misra

Microbial desulfurisation of coal has significant advantages over physicochemical desulfurisation processes since the former process selectively removes the inorganic sulfur compounds and heavy metals without significant carbon loss. The purpose of this study was to improve the desulfurisation yield of a coal sample from northeastern coalfields, Assam, India using microbial technique. The coal sample contained 2.13 per cent of total sulfur and 2.59 per cent of ash. Stirred tank reactors of 40 L capacity were operated in batch mode. Initially, the reactor was fed with 40 L of slurry containing ten per cent (w/v) coal, ten per cent (v/v) inoculum of mixed culture of mesophilic acidophiles, native to coal itself and the requisite amounts of constituents for 9K medium without added ferrous sulfate. The percolate of the reactor was then used to seed the medium for the next experiment. The purpose was to obtain a better adapted and more active biomass which would give a better desulfurisation yield for coal. Further studies were conducted in the bioreactor, fed with 40 L of slurry containing ten per cent (w/v) pulp density of coal, ten per cent inoculum (derived from previous studies) and the medium, supplemented with ferrous sulfate. Results showed an increased total desulfurisation yield of 43 per cent in the latter treatment in comparison to the previous one, where the desulfurisation yield was only 23 per cent. The findings also demonstrated the convenience of using inocula derived from coal, where 50 - 60 per cent of pyritic sulfur was removed, while chemical desulfurisation is of little significance with the majority of coal types. The ash content was also reduced to 1.74 per cent as the low pH of the process caused dissolution of a number of common minerals present in the coal.

Jan 1, 2004

By James Coull, Brian Wilson, David Siddle

"In 2012, Golder Construction Inc. was awarded a Design-Build contract for the design and construction of an extensive, deep ground improvement scheme to support up to 20 metres (66 ft) high Mechanically Stabilized Earth walls and bulk earthworks required for the development of the proposed Kitimat Liquefied Natural Gas (LNG) facility at Bish Cove, British Columbia (BC). Utilizing Cutter Soil Mixing (CSM) to construct barrettes consisting of overlapping rectangular panels of in-situ cement-treated soils, a deep mixing scheme, covering an area of approximately 12,900 m2 (15,430 yd2) and comprising some 1645 CSM panels to depths of up to 30.7 m (101 ft), was developed to provide the required static and seismic stability for the LNG structures, and meet the project-specific performance criteria.CSM panels were constructed through varying thicknesses and discontinuous layers of fine-grained, very soft to soft marine deposits, and loose to compact sands, with occasional interbeds of dense sands and gravels. Panel completion criteria was based on soil response factors, as measured by the CSM equipment, with the design requiring a typical embedment of about 2 m (7 ft) into dense silty sand to sand and gravel to provide the required bearing. A total volume of approximately 73,900 m3 (96,660 yd3) of soil was treated with cement to consistently yield average unconfined compressive strengths exceeding 2.5 MPa (363 psi).This paper outlines the challenges associated with the construction and quality control of this large deep mixing scheme in highly variable geotechnical conditions at a remote location with barge-only access, and limited communication facilities. Specifically the paper will discuss the logistical challenges faced and solutions adopted for the project; equipment redundancy requirements for a 24/7 operation; the impacts of wear and tear, as well as variability in subsurface conditions on productivity; quality control processes adopted for the project, including the value of provision of an on-site laboratory; and materials handling issues, and their impacts on mix design and quality control."

Jan 1, 2017

By D. T. Jordan, L. C. Coetzee, G. Kalenga, T. Mahlangu, W. J. Shipman

Although online free cyanide analysers are widely available and used in gold leaching operations worldwide, reliable automated free cyanide concentration control is not consistently achieved in many of these operations. Effective cyanide concentration control is complex owing to amongst others, the long residence times and ore feed variations. Model Predictive Control (MPC) has been proven to provide superior cyanide concentration control over traditional proportional-integral-derivative (PID) control, leading to savings in operational costs and reduced leachable gold losses. In the first example reported in this paper, MPC has improved control of the free cyanide concentration by keeping it within the required range 73% of the time during testing, compared to the previous PID controller that only achieved this target 30% of the time. This represents a 143% improvement. Another example demonstrates a 22% reduction in cyanide usage as a result of using MPC. MPC functionality is rarely available on the programmable logic controllers (PLCs) and control systems installed at gold plants, hence it is implemented on a personal computer (PC) networked to the cyanide analyser and plant infrastructure. Mintek has developed an embedded MPC that installs into the Mintek Cynoprobe analyser, adding MPC functionality without the need for additional PC and network infrastructure, reducing installation costs. This allows plants to minimise their expenditure on additional infrastructure while gaining the benefits of superior MPC technology for multiple cyanide dosage points. This paper will present results showing that the embedded MPC performs as well as Mintek’s existing PC-based StarCS MPC controller, making it a viable alternative for infrastructure-constrained gold plants. Keywords: Model predictive control, gold cyanidation

Jan 1, 2020

By August E. Vandale

I speak to you today on the subject assigned to me, "Subsidence - a Real or Imaginary Problem", as a representative of Consolidation Coal Company (a wholly owned subsidiary of Continental Oil Company). The information I relate to you is our experience in the Pittsburgh Coal Company Division of Consol and covers the Pennsylvania properties and mines with particular emphasis on the mines in the south- western portion of the State or in the immediate vicinity of Pittsburgh, Pa. Mining of Freeport and Pittsburgh seams of coal in the Pittsburgh vicinity dates back over one hundred years. Consol, or its predecessor, Pittsburgh Coal Company, has been actively engaged in mining in the area since Pittsburgh Coal Company was organized in 1900. Pittsburgh, Pennsylvania came into prominence as the Steel City largely because of the vast reserves of high grade metallurgical coal readily available in the immediate vicinity and also because of its favorable river transportation. Early in the 1900's we operated over 100 small coal mines, with operations located in the Counties of Allegheny, Fayette, Washington, Westmoreland. We have also operated mines in Somerset and Greene Counties. Titles in Pennsylvania can be in three estates: (1) title in fee, (2) title to the mineral, (3) mining rights permitting the removal and extraction of the mineral with or without waiver of surface damage. Consol has over the years acquired good legal title to the coal lands purchased from individual farm owners, with good broad mining rights, and in 98% or more of its title has a complete waiver of surface damage or the right to subside the surface land. In the early days of our Company, individual coal farms were purchased from land owners. Many of these titles severed the coal estate from the in fee title and good mining rights with waiver of surface were conveyed in the original severance deed. Thus, minable coal reserves were put together by the purchase of the coal under many individual farms in an area. In the early years, the mines practiced hand dug mining - later going to mechanical cutting with hand loading of the coal. Systems used were entry driving with room and rib panels. We have practiced full recovery mining as far as practical during the years of hand loading, as well as in the later years when the mines were mechanized. Mining system layouts, methods and procedures have changed from time to time to keep pace with improved mining machinery and new inovations, such as roof bolting and rubber tired haulage.

Jan 1, 1967

By E. H. Burdick

THE difficulties inherent in table concentration operations as applied to gold, silver, lead and zinc ores, are accentuated in the scheelite mill, which has a flowsheet that is similar in general principles. The narrow "spread" in the specific gravity between scheelite and the usual gangue in which it occurs often makes its clean separation extremely difficult and in some cases impracticable. The problem is further complicated by the extreme friability of the mineral and its inordinate tendency to "slime," particularly where fine grinding is necessary and wet grinding methods are employed. The physical aspect of the occurrence of scheelite in the ores, the kind and character of the rock in which the mineral is present, its hardness, friability and the specific gravity of its constituents, as well as like characteristics of the associated minerals-pyrite, pyrrhotite, sphalerite, and others, all have a bearing on the successful milling of crude ores and the production of a concentrate that is marketable with minimum price penalty or none at all. Most tungsten deposits are considered low grade when the limiting factor of low percentage recovery by gravity methods is borne in mind. The great majority of deposits developed or in process of development carry from 0.4 to 1.0 per cent tungstic oxide. Ore carrying I per cent is considered good grade; 0.7 to 0.8 per cent, fair, and below that figure, low grade. Steady mill feed averaging upward of 1.0 per cent W03 is exceptional. Inasmuch as buying specifications demand a 60 per cent W03 content, the mineral content of the ores as mined must be concentrated to at least that degree. A few companies have constructed chemical plants for the treatment of their complex concentrates and low-grade flotation product, but the smaller operator must rely on table concentration, borrowing the tools and to a large extent the methods of his predecessors in the gold, silver, lead and zinc mills. Whether these are the best tools and methods that can be devised is an open question. Except in rare instances, table concentration, however carefully conducted, does not yield a satisfactory final recovery of the mineral content in headings as indicated by chemical determinations of tungstic oxide content. A saving of 60 to 65 per cent is considered fair, and an average 80 per cent recovery, exceptional. Each scheelite ore body is a separate problem. Details of handling that give best results in one case may not be successfully operative at a property on the same contact zone and but a short distance removed. Supplementary treatment of tailings by flotation may be successful in producing a low-grade concentrate of around 15 per cent WO3, which is adapted to further treatment chemically at a given property and entirely unsuccessful at another. This problem constitutes another of the unanswered questions. The following paragraphs relate solely to the beneficiation of scheelite ores by table concentration and supplementary methods.

Jan 1, 1942

By Dewitt T. Ring

Reliable and detailed data covering the enormous number of wells drilled and the long historical production of the state, many of which were never recorded until recent years, render it impossible to gather statistical material suitable for the Institute's standardized form. The total production of crude oil in Ohio for the year was 3,654,503 bbl., which is less than the total production in the United States for the peak day of August 1937. For a period of eight years, from 1895 to 1902 inclusive, Ohio produced more oil than any other state. During the year, 1271 tests were drilled in the state, or 114 more than in 1936. Of these, 317 were oil wells, with an initial production of 7088 bbl., an average of 22.3 bbl. per well; 503 were gas wells, with an initial open flow of approximately 222,441 M cu. ft., or 443 M cu. ft. per gas well drilled; 451 were dry holes, that is, 35 per cent of the total completions. A number of factors account for the steady decline of oil production in Ohio. In the state, at the close of thc year, there were fewer than 28,122 producing oil wells. In 1936, there were 30,150 operated oil wells with an average yearly production per well of 126 bbl. The production for 1937 averaged 130 bbl. per well. During the year, 2028 oil wells were abandoned. In other words, old wells are being abandoned more than six times faster than new ones are being drilled. Since the inception of the oil and gas industry in Ohio, between 150,000 and 160,000 wells have been drilled in the state; new potential territory, offering desirable locations for either oil or gas, is becoming increasingly more difficult to find; the dry-hole percentage will continue to increase. Prices Another factor directly affecting the crude situation during the year was the matter of price and proration of Pennsylvania grade oil. The posted price for Pennsylvania grade in Ohio on June 7 was $2.37 per barrel; at the close of the year, it was $1.70 per barrel, or a reduction of 28 per cent in price. In addition to this price cut, a 50 per cent pro-

Jan 1, 1938

Elongates are commonly used as stope support in South African gold and platinum mines. To evaluate the effect of the inherent strength, stiffness and yield variability associated with elongates, a statistical method is presented which addresses and quantifies the support performance at various levels of certainty. The analysis, which is based on a normal distribution, makes use of force-deformation curves determined from multiple laboratory compression tests on the same support type. The applicability of the method is illustrated making use of actual performance capabilities of various types of elongates. In order to ensure a high probability that support units installed underground exceed the standard support performance curve established by means of laboratory tests, the statistical mean of a suite of tests based on the same support type is downgraded. The ?correction factor? is a function of the mean and standard deviation of the test data, as well as the sample size of units deemed to control the local rock mass stability. It is shown that downgraded performance curves based on a high probability (90 to 95percent) of support units exceeding this performance level are suitable to ensure that the design of support systems will in variably meet the design criteria. In the highly discontinuous hangingwall rock mass typically associated with intermediate- and deep-level mining operations, the interaction between adjacent support units is comparatively limited (at the support spacings commonly used). Therefore, the appropriate sample size (n) of the support units controlling the local rock mass stability should be n= 1. In shallow mining conditions, sample sizes of up to n=5 may be warranted, depending on the spacing of joints and other discontinuities in the hangingwall.

Jan 1, 2001