Search Documents

By A. Himsley, E. Byleveld

"With reference to the chemical constraints underlying the ion exchange process for uranium recovery, a generalized view is presented on the actual and the achievable efficiency of the process. The area considered is restricted to acid leach circuits in combination with nitrate, chloride or sulphuric acid elution.A comparison between actual plant results and the chemical requirements shows that:(a) Unless new and better ion exchange resins are developed, no dramatic change in equipment size and resin inventory is""anticipated. (b) Elution efficiency, especially for sulphuric acid, may be improved considerably. More concentrated eluates may beproduced at lower chemical consumption. A possibility of achieving additional purification solely by ion exchange is discussed.IntroductionThis paper presents a generalized view of the actual and the achievable efficiency of the ion exchange processes for urannium recovery. The study is restricted to acid leach circuits in combination with nitrate, chloride or sulphuric acid elution. The ultimate efficiency attainable with ion exchange is dietacted by the chemical reactions underlying the process. The most sophisticated technology cannot change the diffusion rates in the ion exchange resin nor make the uranium loading exceed its equilibrium valueThe design of an ion exchange plant for uranium recovery involves a considerable number of parameters as a result of the wide variety of pregnant solutions produced from different orebodies. Therefore, a generalized approach of the ion exchange process inevitably neglects some parameters which maylead to significant variations in apparently identical situations.The uranium concentration in the pregnant solution, together with its pH, are the principal variables which determine resin loading and residence rime in the ion exchange system. On the elution side, the type of eluant and its concentration will determine the contact time required and the amount of eluant needed to strip the resin. The temperature, the properties of the ion exchange resin, the total dissolved solids in the feed solution and the competing ions are other variables that affect the chemical performance; these, however, may be considered as a correction of the principal parameters if one is interested only in general trends."

Jan 1, 1980

Operating and Social Considerations from a Contractor?s Perspective

May 1, 2013

By J. Donovan

Underhand cut and fill mining is being planned for selected areas at the David Bell Mine where high ground stresses have resulted in particularly challenging mining conditions. In order to test the placement and performance of a variety of underhand cut and fill paste mats three different designs have been installed and extensively instrumented along the A-Zone 9C ore sill. The sill is approximately 87m long, 4.0m high, and 5.0m average width. The sill was broken into 3 sections each of which will contain one of the sill mat designs. The underhand sill will be mined 3.75mW x 4.0mH, allowing for some overbreak while minimizing the risk of the back span exceeding the design limit of 4.0mW. Each test sill mat includes pre and post-support and includes 0.5m (18?) broken muck mat placed along the sill floor. Upon developing beneath these mats quantitative and qualitative measures will be used to determine which design is the most suitable for application in underhand mining at David Bell.

May 1, 2007

By K. Yoshida

Recently, light magnesium alloy with superior heat radiating ability has been attracting attention in various fields. However cold plastic working of the alloy is very difficult and hot working necessary. Furthermore, the magnesium of products with complicated shapes is difficult, the processing cost is high, and the applicability of the alloy is limited. In this study, a technique for obtaining fine wires and tubes by cold drawing is examined to obtain wires and tubes with high strength, quality and surface morphology, while decreasing production cost. In addition, the shearing strain of magnesium alloy wires and tubes drawn under various drawing conditions was calculated by FEM analysis. It was clarified that cold drawing of magnesium alloy is possible. It was also demonstrated that greater reduction of the cross-sectional area could be realized during cold wire and tube drawing by optimizing the drawing conditions.

Jan 1, 2006

By J. M. Livingstone

"This paper covers some of the problems confronted by Canada's railways in moving bulk materials from their source to the dock-site. The ""cost center"" concept is presented, and hypothetical examples of its use given. Also discussed are systems design, the unit train and pipelines.INTRODUCTIONCANADA LIVES BY RER EXPORTS and the Port of Vancouver by the exports of the Mountain and Prairie Empire at her back. The most recent estimates of off-shore shipments of bulk from the Port of Vancouver rise to 35.8 million shipping tons in 1985 and deep-sea general cargo estimates, in and out, are estimated at 7.6 million shipping tons for the same year. This compares to 7.67 and 2.87 million shipping tons, respectively, in 1965."

Jan 1, 1968

By B. R. Neufeld, M. G. Heximer, S. J. Roach, W. G. Van Luven, D. G. Reynolds

"Teck Metals Ltd. operates an integrated zinc-lead complex at Trail, British Columbia, Canada. In the zinc plant, zinc concentrates are roasted to produce calcine, which is then processed in the leaching circuit for zinc recovery. Calcine is first dissolved at pH <2.0. This is followed by a precipitation stage using additional calcine that removes iron as a ferric hydroxide precipitate which is recycled to the lead operations. It is during this pH adjustment that impurities, notably arsenic, antimony and germanium, are co-precipitated with ferric hydroxide which is the primary removal phase for these elements. Recent processing conditions have resulted in lower iron inputs to the leaching circuit and this has resulted in insufficient co-precipitation of key impurities. This paper summarizes the influence of iron concentrations on impurity removal using laboratory and plant scale surveys, and emphasizes key specification limits for the primary iron removal circuit.INTRODUCTIONThe Sulphide Leach Plant (SLP) at Teck Metals Ltd., Trail Operations produces a zinc sulphate electrolyte from three different zinc bearing streams:1. Calcine, primarily containing zinc oxide, from the roasters2. Zinc electrolyte from the Oxide Leach Plant (OLP) is produced by leaching zinc oxide fume from the pyrometallurgical lead smelting operations3. Zinc slurry from the Zinc Pressure Leach (ZPL) autoclaveThe feed sources are blended and introduced to the iron removal process to precipitate iron in the form of a hydrolyzed iron precipitate which is recycled to the lead smelting operation. Along with iron, impurities, namely arsenic, antimony, germanium and silica, also co-precipitate; this process acts as the primary removal step for these elements. Following iron removal, the electrolyte is further processed in the zinc dust purification circuits. Cadmium and copper are removed in the cold stage circuit via zinc dust cementation, followed by cobalt cementation in the hot stage circuit."

Jan 1, 2016

By R. W. Zeindler, D. A. Fawcett

"A summary is presented of the report completed by the Coal Mining Research Centre in 1980. This report was of a cross-pit conveyor system applied as an auxiliary mining complement to the major stripping unit, a dragline. The purpose of the CMRC report was to evaluate selective mining and replacement of the upper horizons of the strata as an aid in reclamation. These strata were the topsoil, subsoil and glacial till.Past utilization of cross-pit conveyor systems and related engineering studies were assessed. The parameters of the study were based on the mining and geological conditions of the Alberta prairie coal mines. The principal excavator for stripping was a dragline. Excavation of the upper horizons was done by a bucket-wheel excavator discharging onto the crosspit conveyor. Alternative equipment applications were economically compared. Four cases or geological sections were evaluated in detail. The economics of the alternative mining systems for each of the cases were determined. In all instances, the most economical solution was a tandem system utilizing a dragline with a bucket-wheel excavator/ cross-pit conveyor system."

Jan 1, 1981

By A. Dahi Taleghani, Amir Shojaei

A continuum damage mechanics (CDM) based constitutive model has been developed to describe elastic, plastic and damage behavior of rock during drilling. In addition to inelastic deformations, this model incorporates rock anisotropies like toughness anisotropy due to the bedding planes orientation that is a common observation in soft Shales. The pressure sensitive inelastic deformation of porous rocks together with their damage mechanisms are studied for drained and undrained conditions. Fracture mechanics of microcrack and micro-void nucleation and their coalescence are incorporated into the formulation of the CDM models to accurately capture different rock failure modes. The performance of the developed elastoplastic and CDM models are compared with the available single cutter test data of a specific shale play and then the models are introduced into a commercial finite element package through user-defined subroutines. A workflow to derive the required model parameters is presented through inverse modelling of the single cutter test data. The developed CDM model outperforms the traditional discrete element and fracture mechanics approaches by removing stress singularities at the fracture tips and simulation of progressive fractures like formation of the cuttings ribbon without any essential need for remeshing. This model would provide a robust tool for modeling bit performance and rate of penetration using conventional elements of FEA with a reliable results and a computational cost less than similar computational techniques like discrete element methods.

Jan 1, 2015

By H. Soto, P. Lacombe, R. del Villar

"During the summer of1989, Les Mines Selbaie, with the cooperation of Université Laval initiated a research project to evaluate the column flotation technology for its concentrator near Joutel, Quebec. The experimental work involved both a 5 cm by 11 m laboratory column and a 45 cm by 10 m home-made pilot unit Amenability tests were conducted using both units on various streams of the plant. Results showed that columns are not suitable for the copper cleaning circuit because the loss of precious metals, associated with the rejected pyrite, overcome the improved copper metallurgy. On the other hand, column testing at the zinc circuit showed improved zinc selectivity.Scale-up testing was&apos;, therefore, conducted on the first zinc cleaner concentrate using the laboratory-size column. The influence of variables such as porous parger grain size, wash water flow rate, airflow rate and froth depth values on column performance was&apos; first assessed. Scale-up parameters were then determined using the optimal operating conditions from the previous tests. Simulation facilitated the determination of the most convenient plant-scale column arrangement.A number of conclusions concerning the experimental determination of scale-up parameters are also presented."

Jan 1, 1993

By A. B. Carino

Gulf Minerals (Canada) Limited&apos;s Rabbit Lake uranium operation is located in the northern portion of Saskatchewan, 198 miles southeast of Uranium City and /34 miles northwest of Lynn Lake, Manitoba. The paper follows the ore flow through crushing, grinding, sulphuric acid leaching, countercurrent decantation, solvent extraction, ammonium diuranate precipitation, thickening, drying and tailing neutralization.

Jan 1, 1979

By K. G. Chipman

The Geological Survey is the oldest map making department in the Canadian Government service, and when organized in 1842, one of the first principles to be recognized was the absolute necessity of having good maps. The primary purpose of the Survey has always been geology; but because a graphic representation by means of maps makes the written report .more readily intelligible; because the correlation of known geological facts is often difficult or nearly impossible unless they can be represented on a map; and, because the public demand information shown in this way, the Geological Survey must continue to supply maps; and the supplying of these maps must be considered as an essential part of the work of the Survey. It is a commonly recognized principle of pedagogics that an appeal to the eye is quicker than one to the ear; that children (and others) learn more quickly when a thing is presented to them through the eye rather than through the ear. The application of this principle to the work of the Geological Survey is that, to a large number of people, the message of a map is more quickly grasped, is more readily intelligible, and is in many ways of more interest and value than is the same information in a report. I do not mean that the maps are of more importance than the reports.

Jan 1, 1924

By Michael L. Free, Zongliang Zhang, Joshua M. Werner

In the copper electrowinning process, short-circuiting between the anodes and the cathodes is a critical problem that changes the current allocation among local electrodes and reduces the current efficiency significantly. Possible reasons for the short-circuiting include the improper alignment of the electrode, bent electrode, and nodules on the cathode surface. In typical tankhouses, there is often a time between shorting and harvesting as well as between shorting and clearing. Therefore, it is inevitable to have short-circuiting affect the operation performance in practical electrowinning operations. However, one key piece of missing data is the actual measurements of the current efficiency as short-circuiting is approached and allowed to continue. Consequently, short-circuiting tests that allow tracking of electrowinning parameters before and after short-circuiting were performed in a laboratory scale Cu electrowinning cell. In the tests, the electrode spacing change, the mass of electrodeposited Cu, the deposition morphology, and the current allocation as well as the current efficiency before and after short-circuiting were studied. Results show that the short- circuiting affects the current allocation and the current efficiency significantly. Moreover, it changes the Cu deposition on the short-circuited cathode and therefore causes problems for Cu electrowinning. INTRODUCTION Electrowinning (EW) is commonly used for copper production around the world, with a rated production from 120,000 to 200,000 tons per year per operation (Wiechmann, Aqueveque, Henríquez, Muñoz, & Morales, 2014). In Cu electrowinning, Cu ions in the electrolyte are reduced on the cathode surface as metallic copper with a DC current, while on the anode, a counter anodic reaction occurs with oxygen gas generation (Werner, Zeng, Free, Zhang, & Cho, 2018; Zhang, Werner, & Free, 2018; Zhang, Werner, & Free, 2018). In copper electrowinning, an average current density of 200 to 400 A/m2 is applied to the electrowinning cell (Wiechmann et al., 2014). As the Cu deposits on the cathode, the distance between anode and cathode reduces and most of the time, short-circuiting forms between some anodes and cathodes in a large tankhouse containing thousands of electrodes, reducing the current efficiency and increasing the energy consumption significantly. The current efficiency in well-run copper EW operations is typically above 90 %. Most of the unused current is wasted through short circuits, stray currents, and by-byproduct formation (Davenport, King, Schlesinger, & Biswas, 2002; Wiechmann, Vidal, Pagliero, & Gonzalez, 2002; Wiechmann, Morales, & Aqueveque, 2010). Usually, in the tankhouse, the short-circuiting increases the current in the involved cathode by up to 1500 A (Wiechmann et al., 2010). Multiple reasons can cause the short-circuiting in the cell, and the most common reasons include the uneven current distribution among cathodes, tilted electrodes, bent electrodes, and nodules formed due to the large deposition roughness. Recognition of this challenge in the Cu electrowinning process has led researchers to perform many investigations on approaches to avoid and reduce the short-circuiting in the cell. A series of research investigations have been conducted to develop and improve a new type of intercell bar for Cu electrowinning (Wiechmann et al., 2002; Wiechmann, Morales, Aqueveque, & Burgos, 2007; Wiechmann, Morales, & Aqueveque, 2009; Wiechmann et al., 2010; Wiechmann et al., 2014). The associated test results show that this new design limits the occurrence and magnitude of short circuits and allows operation at higher current densities. Sandoval, Clayton, Dominguez, Unger, and Robinson (2010) stated several keys to control short circuits, such as maintaining the straightness of the cathode, removing “edge hair” from the cathode starter, and maintaining electrode alignment in the cell. Prengaman and Siegmund (1999) from RSR technologies developed a new Pb-Ca-Sn anode to prevent the anode deformation, thereby reducing the short-circuiting in the Cu electrowinning cell. Although the negative effects of short-circuiting on the Cu electrowinning have been recognized, and various investigations have been conducted to address this issue, the actual measurements of the electrowinning behavior and performance as short-circuiting is approached and allowed to continue are seldom reported. However, in typical tankhouses, there is a time between when shorting occurs and harvesting/clearing are performed. One key factor in determining the harvest time is the frequency of shorting. Consequently, we have performed short-circuiting tests that allow us to track electrowinning parameters before and after short-circuiting.

Jan 1, 2019

By M. A. Bérubé, M. Choquette, P. W. Godbehere

"RESUMELa scorie produite par le procédé pyrométallurgique d&apos;extraction Noranda contient environ5% de cuivre. Elle est traitée comme un minerai conventionnel de cuivre au concentrateur de Mines Noranda et les rejets de flottation présentent encore des teneurs souvent supérieures à 0.3% en cuivre. La scorie est principalement constituée de magnétite, de fayalite et d&apos;un verre siliceux. Bien sûr, Ie cuivre y est majoritairement sous forme de sulfures et d&apos;un peu de cuivre métallique. Le verre contient toutefois un peu de cuivre en solution, de 0.14 à 0.33% en moyenne, selon l’echantillon examine, ce qui représente à peine 1% de tout Ie cuivre de la scorie. Dans les rejets de flottation, cela justifie par contre de 15 à 25% des pertes totales en cuivre, Ie reste se retrouvant sous forme de tres petits globules de sulfures de cuivre ou de cuivre métallique, en moyenne de 2 à 3 micromètres de diamètre et bien emprisonnes dans Ie verre.SUMMARYThe slag produced by the Noranda continuous smelting process usually contains about 5% copper. It is processed as a conventional copper ore at the concentrator of Noranda Mines. The flotation tailings still often contain more than 0.3% Cu. The slag is mainly constituted by magnetite, fayalite and a siliceous glass. Evidently, the copper occurs mostly as sulphides and, to a lesser extent, as metallic copper. However the glass contains a small amount of this metal in solution, between 0.14 and 0.33% on an average, depending upon the investigated sample. This represents scarcely 1% of the total copper in the crude slag, but as much as 15 to 25% of this metal in the flotation tailings, in which the major part of the copper occurs as very small globules of copper sulphides or metallic copper with an average diameter of about 2 to 3 um and well-locked in the glass."

Jan 1, 1987

By J. G. Conaway, P. G. Killeen

"Gamma-ray spectral logging, a useful technique for uranium exploration and evaluation, has generally been underutilized by the Canadian mining industry. Provided that the technique is properly applied, it is capable of yielding reliable quantitative information regarding the distribution of uranium and other radioelements along the borehole under most conditions.In practice. there are numerous factors which potentially can degrade the quality of the log and thus any quantitative interpretation based on it. Fortunately, the appropriate choice of logging equipment and technique can avoid many such problems, and corrections can be applied to the data to compensate for most of the others."

Jan 1, 1980

By Denis Beaudoin

Program Basics: Goals, Course Content & Training Process Sudbury: History of the Program & Lessons Learned Diavik: History of the Program & Lessons Learned Most Recent Program: Totten Mine in partnership with Sagamok Anishnabek Summary -Lessons Learned Conclusion

Oct 1, 2010

By M. W. Gilmore, J. Ndlovu, T. Sepoloane, Anglo American Platinum, L. R. Nelson, R. N. Varty, L. J. Bryson, B. Peyper, J. P. Hagemann

"As part of Anglo American Platinum’s Rustenburg Base Metals Refinery (RBMR) expansion, a new Nickel Electrowinning Tank House, with a nameplate capacity of 32 400 tons per annum, was constructed. Commissioning of the new electrowinning technology, which involved world first full deposit plating, commenced in 2011.The old nickel electrowinning process at the RBMR used starter sheets which, along with a divided cell configuration, was very labour intensive and exposed operators to high levels of aerosols that contained both nickel and acid. To overcome this problem two key design intents of the new technology are aerosol abatement and minimising labour in the electrowinning cell environment, with a design target to reduce the nickel occupational exposure limit (OEL) to half the legislated limit of 0.1 mg.m-3.Commissioning of the new technologies adopted to achieve mist abatement is described, together with a review of technical and operational challenges relating to the titanium blank edge strips, blank roughness and sandblasting optimisation, blank quality control, electrode spacing, polyconcrete cell dimensional stability and cell top furniture. The impact of these on process performance is presented and the development of fault checking and rectification methods, to maintain high process performance, is explained.INTRODUCTIONThe expansion of Anglo American Platinum’s Rustenburg Base Metals Refinery necessitated the construction of a new Nickel Tank House to achieve two primary objectives, namely increasing the nickel electrowinning capacity from 22 500 tons per annum (tpa) to 32 400 tpa nickel, and a design to reduce the nickel aerosols to 0.05 mg.m-3 as a time weighted average over 8 hours, which is half of the legislated occupational exposure limit (OEL) of 0.1 mg.m-3."

Jan 1, 2016

By Bruce C. Fielder

"The concentration of uranium in orebodies discovered in the Athabasca Basin of northern Saskatchewan over the last 20 years has increased by a factor of 100. These high grade uranium orebodies are associated with high concentrations of radionuclides, complex mineralogy and an elemental makeup that includes base metals, arsenic, and molybdenum. Exploiting these high grade ores has required metallurgical advances in milling, tailings disposal and effluent treatment as well as changes in the design of uranium mills.This paper describes the most significant advances, including advances in dealing with the environmental issues which have become more prevalent in recent years. The milling processes of the Cluff Lake Mill, Key Lake Mill, Rabbit Lake Mill, and McClean Lake Mill are compared to illustrate both similarities and differences necessary for milling different orebodies.BackgroundUranium mining in Saskatchewan started in 1953 when the Beaverlodge Mine, owned by Eldorado Nuclear Limited (Eldorado), came into operation at Uranium City. Development in the Athabasca basin started in 1975 when the Rabbit Lake mine came into operation. This was followed by the start-up of the Cluff Lake mine in 1980 and the Key Lake mine in 1983. The McClean Lake mine is forecast to start up in the near future. The McArthur River mine recently received construction approval and the Cigar Lake Project and the Midwest Project are currently in the environmental approval process.The Beaverlodge operation ceased production in June 1982 after nearly 30 years of operation. The Rabbit Lake mill processed Rabbit Lake ore from 1975 until 1985, Collins Bay R-Zone ore from 1985 until 1993, and is currently processing ore from the Eagle Point mine (Bharadwaj, Jarvi and Lam, 1996). The Cluff Lake mill processed ore from the D- Orebody from 1980 until 1984. Since then the Claude orebody has been processed and the OP and DS orebodies are presently being milled (SRK. Senes and Melis, 1987; and Cogema Resources Inc. 1994 ). The Key Lake mill processed ore from the Gaertner ore body from 1983 until 1989 and Deilmann ore has been processed since (Cameco Corporation, 1992b and I 994a). Processing of McArthur River ore in the Key Lake mill is scheduled for 1999. The McClean Lake mill will be processing ore from the JLR, Sue and McClcan orebodies associated with the McClean Lake mine. In future ore from the Cigar Lake and Midwest projects will be processed in the McClean Lake mill. (Minatco Limited. 1991a)."

Jan 1, 1998

By Noel G. Thomas

"This paper will identify where the industry is heading with iron· ore in the next ten years. From a customer&apos;s point of view, an indication of the changing, yet expanding, market will be made. This will progress further into the most likely changes in chemical and physical requirements of the ore products. No definite target can be set for 1990, but the logic from the direction of the changes will be established.IntroductionThe tonnage and quality of iron ore produced in the eighties will be heavily influenced by energy and investment considerations. That&apos;s not a great pronouncement, but this paper will explain how these two factors are :(I) influencing a disproportionate growth of electric furnace capacity and a greater use of scrap for iron units, in place of Iron ore;(2) influencing chemistry specifications; and(3) causing extensive examination of ore agglomerate form. Inflating investment costs are emphasizing the need for more productive blast furnaces, and the iron ore burden is under heavy examination as to how it affects productivity and coke rate."

Jan 1, 1981

By K. Thuro, L. Wilfing, H. Kasling

"In mechanized tunneling, performance prediction is a crucial issue for estimating excavation costs and construction time of a tunnel project. The aim of this work is to compare the calculated parameters by penetration prediction models with the results of penetration tests during excavation by a Tunnel Boring Machine (TBM) at actual tunnel projects. This comparison helps to improve the existing prediction models (Gehring, 1995 and Rostami (Colorado School of Mines), 1997.) and to develop a new, so-called “Alpine Model” (research group ABROCK; Schneider et al., 2012).On-site penetration tests are a common tool to determine performance of a TBM in certain geological environments. During a test, the TBM is operated under defined conditions that allow comparing the results of different projects and machine types. There are two different types of penetration tests in use. The more common type, described by Bruland (1998a), is based on test drives at different thrust levels. The tests in this study are performed as start-stop-tests, meaning that the TBM starts from zero to the maximum possible thrust and reverse with slowly increasing respectively decreasing steps (Frenzel et al., 2012). To gain information about the interaction between TBM and rock mass, a detailed geological documentation including an analysis of the discontinuity pattern and laboratory testing for rock strength characterization are mandatory.Within the last year 16 penetration tests have been performed. The results are thrust- penetration curves (Figure 2) showing that up to a certain penetration rate only crushing occurs (subcritical penetration). From there the desired rock fragmentation process called chipping takes place (Frenzel et al., 2012). These two different fragmentation processes can be described best by a bilinear function as seen in Figure 3. Both, CSM- and Gehring-model, do not fit to the trend of the penetration rates determined during the excavation process as they are using potential or simple linear functions.Another parameter that has to be implemented into the new prediction model is the influence of discontinuities. In case of favorable orientation and spacing, discontinuities reduce the required thrust at same penetration rates. In contrast, unfavorable discontinuity systems can cause blocky faces and hence worse performance than predicted. Besides discontinuities, the toughness of rocks has to be taken into account when predicting the penetration as tough rocks need more energy to obtain complete failure than brittle rocks.Key advantage of these tests in comparison to existing are more data points in less time. By improving respectively extending the existing penetration prediction models with the stated parameters, the penetration prediction for TBMs can be more accurate and also wear calculation can benefit from this approach."

Jan 1, 2015

By R. W. Seedsman

In 1984 and 1985, two 7.6m diameter TBM tunnels were driven from the Donkin-Morien peninsula in Nova Scotia to access the Harbour coal seam. The design of the ground support was based on identifying zones of rock failure through the application of the Hoek Brown failure criterion and the early use of finite element analyses. In 1992, the mining project was abandoned and the tunnels allowed to flood. Monitoring data from the tunnel was subsequently used as a case study in the development of the concepts of brittle rock behaviour. In 2007, the tunnels were pumped out as part of a feasibility study into the reintroduction of longwall mining into the coalfield. There is a good match between observations of the collapse zones in the roof and sides of the tunnel and a simple elastic analysis using brittle parameters, a spalling limit of 5, and a low independent shear modulus. The brittle analyses form the basis of the design for the resupport of the tunnels.

May 1, 2009