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By S. A. R. Keneti

Predicting the geomechanical response of the shale gas material during hydraulic fracturing operation in the field needs better understanding of their geomechanical behaviour under laboratory testing. Anisotropy is considered as a critical factor during investigation and analysis of deviated boreholes, borehole stability, stress-strain and strength behaviour, generation and propagation of fracture and fluid flow. In this study, compressive elastic modulus (Ec) of the Montney shale has been investigated in two perpendicular directions: unconfined compressive strengths test was conducted on the Montney sample to measure its Ec in the vertical direction. This value then was compared to the Ec value in the horizontal plane (i.e. foliation plane) which was previously measured throughout a Brazilian test by Keneti and Wong (2011). From the results, the representative values of Ec in the vertical and in the horizontal directions were found as 25 GPa and 40 GPa, respectively. Computer tomography technique was also employed for the experimental data interpretation.

Jun 1, 2012

By Steve T. Laflin

Since the beginning of the nuclear era, there has never been a commercial solution for the large quantities of depleted uranium hexafluoride generated from uranium enrichment. In the United States alone, there is already in excess of 1.6 billion pounds of DUF6 currently stored. INIS is constructing a commercial uranium processing and fluorine extraction facility. The INIS facility will convert depleted uranium hexafluoride and use it as feed material for the patented Fluorine Extraction Process to produce high purity fluoride gases and anhydrous hydrofluoric acid. The project will provide an environmentally friendly and commercially viable solution for DUF6 tails management.

Aug 1, 2010

By S. Radacina Rusu

The satellite-based global positioning system (GPS) has significantly changed the way site operations are carried out in surface mining. The GPS has impacted safety, productivity, fleet efficiency, and maintenance practices. However, no comparable global localization system exists for underground mines. This paper discusses recent work in the application of ideas from the mobile robotics research community to the problem of real-time vehicle positioning in underground drift networks. Related previous work recently focused on the creation of globally consistent 2D maps of underground environments that possess sufficient detail to be used for underground localization. Our current work entails the development of a GPS-like system for mobile mining equipment, with results given from both laboratory and field experiments.

May 1, 2011

By G. F. Trainor

The complex ore body at CNRL?s Horizon mine presents some unique challenges in managing ore and waste delivery. With 25m x 25m ore blocks shovels often take bucket loads from multiple blocks to fill one truck load. With CNRL monitoring 22 different qualities per material a precise calculation of the blended quality of ore on the back of each individual truck is essential to meet the daily blend requirements at the plant. Additionally, one of these qualities must be closely monitored and controlled at a singular level as delivery of certain grade and quantities can cause serious disruptions at the plant. The waste material also requires special handling and delivery for its use in dyke construction for tailings impoundment. Shale materials used in the construction contain high levels of saline that must be contained to prevent seepage into ground water. This paper will discuss how the use of Wenco?s survey-grade GNSS system on shovels, its dispatching algorithm, and fleet management applications give CNRL the ability and confidence to control and report on these three issues.

May 1, 2013

By Vladislava A. Ignatkina, Victor D. Samyguin

"Within the limits of two-phase approach, considering mass transfer with pulp and air streams was shown that each bubble appears to be an elementary carrier, transporting particles from the collection zone into the froth. The kinetics of flotation was described by the exponential equation in which first order flotation speed constant has to be replaced with two-phased coefficient of a mass transfer. Criteria of selectivity of two ore fractions separation, based on determination of optimum time at which maximum difference between extractions and components content in separated fractions were offered. An interrelation between optimum time of pulp residence in a flowing chamber of a flotation machine, time of bubbles mineralization and an optimum airflow has been ascertained. Cumulative criterion of mass transfer efficiency of flotation process has been ascertained to be a form of the spectrum and its position on axis of three-phase coefficient of a mass transfer.INTRODUCTIONRegularities of a mass transfer of three bearing streams: pulp stream, air stream and froth stream underlie theory of mineral complexes flotation (Samygin, Filippov, & Shekhirev, 2003)However, only description of mass transfer in pulp stream by means of kinetic equations that were simple and convenient for practical use, has gained a full distribution (Tykhonov, 2009;Rubinstein&Filippov, 1980; Saleh, 2010).Within the limits of a single-phase approach, the role of gas stream in increase of speed and selectivity of flotation, was associated with an improvement of hydrodynamic mode. An influence of particles and bubbles sizes (Rubinstein&Filippov, 1980; Rubinstein&Samygin, 1998, Samygin et al., 2003; Dai, Fornasiero,& Ralston, 2000), of pulpflow and airflow (Finch& Dobby, 1990) and turbulent energy intensity (Shubert, 1979; Massinaei, 2007) on the flotation process has been studied. It was stated that flotation selectivity is increasing by means of gradual airflow increase from first to final cameras of the impeller flotation machine (Aslan&Boz,2010; Finch, 2011) and by means of using a multizone flotation machine (Samyguin, Filippov, Matinin, Lekhatinov, &Tertyshnikov, 2013)."

Jan 1, 2016

By J. Warner, K. A. Hughes, P. E. R. Blanchard, J. Esslifie-Dughan, J. W. Reid

Tailings management plays an important role in reducing the environmental impact of Orano Canada’s uranium mining operations in Northern Saskatchewan. Uranium ores mined from Northern Saskatchewan are often associated with large amounts (10-20 wt%) of other harmful elements, such as arsenic and nickel. The JEB Tailings Management Facility (TMF) located at McClean Lake, Saskatchewan is designed to prevent potentially harmful water-soluble elements, particularly arsenic, from contaminating the surrounding environment by promoting the formation of water-insoluble minerals. It is therefore important to determine which arsenic-containing mineral species are present in the TMF and how they evolve over time. Researchers at the Canadian Light Source (Saskatoon, Saskatchewan) were successful in identifying the arsenic mineral species present in tailings samples collected from the TMF in 2013 using X-ray absorption near-edge structure (XANES) spectroscopy. XANES analysis verified that the majority of arsenic species in the TMF existed as amorphous and crystalline ferric arsenates with minor amounts of arsenite and arsenide species. Herein, XANES is again used to analyze a new set of tailings samples collected from the TMF in 2018, specifically focusing on the difference in the distribution of arsenic species in old and new tailings.

Jan 1, 2020

By Troy Boisjoli, Sean Hillacre, Matt Batty

Discovered in 2014, the Arrow Uranium Deposit has undergone rapid development through successive drilling programs informed by geostatistical drill hole spacing studies. An independent third-party geostatistical drill hole spacing study was completed by Clayton V. Deutsch Consultants Inc. in 2017, evaluating the uncertainty of thickness, grade, density, and areal limit of the Arrow Deposit to determine a drill hole spacing suitable for Indicated Mineral Resources. Indicated spacing was defined to be 24 to 32 metres (“m”) to be within 15% of predicted for a nominal quarterly production volume with a probabilistic tolerance between 75 and 90%. The study not only defined the Indicated Mineral Resource resultant from the 2016 drill program, but also provided drill hole targeting criteria for subsequent drill programs aiming to convert Inferred to Indicated Mineral Resources. A subsequent geostatistical drill hole spacing study on the Arrow Deposit was completed by Clayton V. Deutsch with Resource Modeling Solutions in December 2018 to define Measured Mineral Resource spacing in support of the 2019 drill campaign. The study resulted in a drill hole spacing of 9 to 17 m to be within 15% of predicted for monthly and quarterly production volumes using an accepted industry probabilistic tolerance of 90%.

Jan 1, 2020

The dynamic breakage process of rocks by the impact of a hydraulic hammer is more complex than one normally assumes. It is even more difficult when one has to conduct the breakage under water. In such cases one does not know exactly what the surface topography and composition are at the bottom of the sea or river and, hence, it is more difficult to select the best position of the hammer before starting the hammering. Typically, an industrial hammer has a diameter of about 250 mm, a length of about 1.25 to 1.75 m and a mass of several tons. The hammer frequency can be up to 50 impacts per minute. The general principles of rock hammering can be easily summarized, but this knowledge is not sufficient to adapt adequately the method for less common rock conditions (e.g. less brittle rock, presence of vertical and subvertical fractures, etc.). That is the reason why we initiated a research project, whereby a scale model has been developed to conduct experiments in the laboratory and whereby discrete element simulations are being conducted. Both aim at a better understanding of the basic mechanisms of rock hammering. The scaled experimental model allows varying the impact energy and the static weight independently. Within the experiment, the hammer is in contact with the rock specimen under a certain confining pressure and with a certain contact pressure due to the static weight. A weight falls on the hammer, creating the dynamic action or impact; the height over which the weight falls can be varied. The penetration is recorded after each impact. After a certain penetration the test is stopped and the internal crack patterns are described. Some simulations have been conducted, allowing the modeling of individual fracture initiation and growth during the penetration of the hammer by either a constant displacement rate (using the UDEC-code) or by introducing the dynamic process (using the PFC-code). Some of the observed features in the laboratory experiments can be visualized in the simulations. However, further research is needed to allow the simulations being an adequate tool to well understand the dynamic process in laboratory experiments, as well as the in-situ behavior.

Aug 1, 2013

By O. Hungr, V. Gischig, G. Preisig

Deep-seated landslides are characterized by slow time-dependent movements induced by constant gravitational creep, and periods of acceleration associated with stress changes within the rock and the preexisting fracture network. Natural stress changes are typically caused by seasonal variations in surface temperatures and groundwater pressures, but also by rare and more violent events such as earthquakes. These processes are responsible for cyclic loading and unloading that leads to rock mass damage, fatigue and progressive failure with time, and may explain sudden, unexpected rock slope acceleration phases. In this work, we present a set of distinct-element models to investigate and compare the role of hydromechanical fatigue and seismic fatigue in the history of a deep-seated landslide. Hydromechanical fatigue arises from the fluctuation of pore pressure in fractures accompanying periods of significant groundwater recharge. In alpine areas, there are usually one or two cycles per year associated with snow melt and intense rainfall periods. In the presence of a deep confined aquifer within the rock slope, the amplitude of pressure fluctuations may reach values of 0.25-0.5 MPa. Hydromechanical models considering such pressure changes are able to reproduce observed slope accelerations-decelerations phases. Substantial accelerations may occur even in the absence of a cycle of exceptional amplitude, depending on the current state of fatigue. At a given time, one or more fractures may be critically-stressed, and a small change in applied stress is enough to cause local failure and induce a crisis of enhanced slope acceleration. This is augmented if the rock slope contains planes of weakness associated with its tectonic history, glacial debuttressing, etc. The corresponding behaviour is analogous to laboratory experiments on rock and metal fatigue. Similar fatigue effects have also been proposed for repeated earthquake events in seismically active regions. Unlike hydromechanical stress changes that occur in a more localized portion of the rock slope, those induced by passing seismic waves involve the entire rock mass. Moreover, the frequency and amplitude of stress perturbations due to earthquakes are different than those induced by pore pressure variations, although both likely contribute in combination to the degradation and progressive failure of large deep-seated landslides when both are present. The results presented illustrate that: (1) assessment of slope stability near critical infrastructure (e.g., hydroelectric reservoirs) should not only consider static stability, but also failure mechanisms related to fatigue that evolve over time and may result in an apparently stable slope progressing towards a critical state due to relatively small but repetitive stress changes; and that (2) characterization of fatigue processes affecting a deep-seated landslide requires multiparametric continuous monitoring at different observation points.

Jan 1, 2015

By O. G. Olvera, D. G. Dixon, E. Asselin, L. S. Quiroz

Dissolution rates of chalcopyrite (CuFeS2) were calculated using electrochemical impedance spectroscopy (EIS). The calculated dissolution rate decreased by a factor of 3.2 after the electrode was passivated. The results presented in this work indicate that the reduction of Fe3+ was the rate-controlling step for fresh CuFeS2 electrodes while the transport of cations within the passive film limited the dissolution rate for the passivated electrode. The transfer of cations at the electrode/electrolyte and passive film/electrolyte interfaces did not affect the dissolution rates of the fresh and passivated CuFeS2 electrodes, respectively. The catalytic effect of pyrite (FeS2) on the dissolution of CuFeS2 continued after the passivating treatment. The contact of fresh and passivated CuFeS2 electrodes with different FeS2 particles resulted in increased dissolution rates, due to an increase in the reduction rate of Fe3+.

Jan 1, 2014

By W. G. Robinson

"MINING is one of Canada's most important industries and exploration is the life-blood of this dynamic and exciting business. The health and growth of the mining industry of tomorrow depends on the effort and thought that go into exploration today. The Members of the Geology Division of the C.I.M. are directly concerned with exploration, and it is fitting that this Division should periodically sponsor reviews of the thoughts and practices of the exploration com-munity. Accordingly, we have invited seven leading authorities to contribute papers dealing with specialized aspects of this field.Exploration is a science, or art if you will, that is constantly changing in keeping with our expanding knowledge of geology and technology. It started with the old-time prospectors who searched the wilds for exposures of ore, and made finds that developed into some of our most important mining camps. As more discoveries were made, they were able to relate certain types of deposits with particular geological conditions, laying the foundation for modern concepts of economic geology. The mapping by the early field parties lacked detail and usually served to outline the ""greenstone"" areas considered favourable for prospecting. More de-tailed studies through the years by government and company geologists led to new thoughts on the origin, emplacement and geological control of orebodies. The continuing diversity of opinion on these subjects indicates a need for further research, but each year sees an increase in our reserves of factual information."

Jan 1, 1967

By R. B. Allen, B. S. W. Buffam

"The property of Chesterville Mines, Limited, is in McGarry township, Timiskaming district, Ontario, about 25 miles east of Kirkland Lake. It consists of a group of fifteen claims that extend northeast from the KerrAddison mine for a distance of 2 miles.In June, 1906, two groups of prospectors left the town of Chesterville, Ontario, to prospect in northern Ontario. Silver had been discovered 3 years before at Cobalt and the large profits of this young mining camp were the principal incentive to extending the field of exploration northward. One group consisted of Dr. Reddick, Edward Flynn, John Hummel, William Knott, and Colin Cameron. The other group comprised J. T. Kearns, Herman Hummel, W. G. Barkley, and J. Elliott.The two groups travelled north by train to Haileybury and thence to Larder lake by canoe. Camps were pitched on the northeast arm of the lake, and within a short time a discovery was made by Edward Flynn of the first party, who found gold on the property now owned by Kerr-Addison Gold Mines, Limited. Herman Hummel and J. T. Kearns shortly afterwards made the second discovery, on what is now the Chesterville property. These discoveries, made some years prior to those at Porcupine and Kirkland Lake, are believed to be the first in that part of northern Ontario.The Hummel-Kearns claims were incorporated in the following year under the name of Chesterville Larder Lake Gold Mining Company, Limited. It was not, however, until 30 years later, in 1936, following the increased premium on gold, that sufficient capital was placed in the treasury of the Company to carry out an extensive diamond drilling programme. This exploratory drilling was started early in 1937 under the direction of Leo. J. Kearns, and a large body of ore was intersected in the first drill hole. Underground work was started in 1938, a mill was built, and the first gold brick was poured on July 29th, 1939."

Jan 1, 1954

By M. Remillard, M. Garon, M. Thérien, D. Hodouin

"Nineteen streams in the copper and zinc flotation units of the concentrator of the Matagami division of Noranda Inc. have been sampled for particle size distributions chemical assays, and gold and silver contents in each particle size interval. The data are upgraded by the mass balance package BILMAT. These results, in conjunction with microprobe analyses, are used to quantify the silver losses in the copper clean¬ing flotation stages and to determine how overall silver and three silver-bearing minerals are recovered in the plant final products.RESUME Dix-neuf produits des circuits de flottation du cuivre et du zinc de la division Matagami de Noranda Inc. ont été échantillonnés pour leur distribution granulométrique, analyses chimiques et le contenu d'argent et d'or des fractions granulométriques. Le bilan métallurgique a été obtenu à l'aide du programme BILMAT. Ces résultats couples avec une etude minéralogique à la microsonde sont utilises pour quantifier les pertes argentifères aux diverses étapes de nettoyage du circuit de cuivre et pour de¬terminer la repartition de l'argent et des trois minéraux argentifères dans les produitsfinals de l'usine.INTRODUCTION The Matagami division of NORANDA INC. produces copper and zinc concentrates from a sulphide ore which contains a small amount of gold (0.34 g/t) and silver (20 g/t). Only a small part of the silver (~-30%) is presently recovered in the copper concentrate. The objective of this study is to evaluate the metallurgical behaviour of silver, and secondarily of gold, in the flotation circuit for a possible increase of its recovery in the copper concentrate to improve its economic value. For that purpose it is worthwhile to study the minerals which bear silver and to determine the critical flotation stages where they are lost in the tails. The methodology proposed here is based on a coupling of a mineralogical study and a detailed mass balance calculation in the flotation circuit."

Jan 1, 1986

By Ning Yu

There are about 1.341 trillion tons (t) of proven coal reserves in China, of which 279.58 billion t are available for mine well construction basis. Thick coal seams are 44% of the reserves. The production of thick coal seams exploitation is over 45% of the total coal production. Full-seam mining and fully-mechanized mining for large mining height is the technology development direction of thick and extra thick seam mining. It is also the important way to achieve efficient and intensive mining with the characteristics of high production, high mechanization, high efficiency and low energy consumption, etc. Complete set of technology and equipment of fully-mechanized top caving for large mining height of full-seam (7m) mining and extra thick seam ( 14-20m) has been gradually mature and for demonstration application by the joint research of government, enterprises, universities, scientific research organizations and users. It has solved some technical problems of coal face for large mining height (over 7m) such as the coal wall spalling control, stability of support, wall rock coupling, cooperation work of mining and caving, full roadway support for super large section, end support, equipment matching of coal shearers, hydraulic support and scraper conveyor. It has developed key equipments including powerful hydraulic support of fully-mechanized mining and fully-mechanized top caving for large mining height, electrically-driven coal shearer with high speed and reliability, scraper and belt conveyer with big capacity, soft-start and high reliability, automatic control system of coal face with the core of electric-hydraulic control, bolting drill boom large section coal roadway shearer, heavy auxiliary transport equipment. The operation rates of fully-mechanized top caving equipment for full-seam and large mining height are 94% and 92.1%, and recovery ratios are 93.6% and 88.9% respectively. The annual raw coal production of single work face is over 10 Mt. The automation and intelligentization level have been clearly improved. The exploitation of thick and extra thick coal seam that is safe and efficient has been achieved in China.

Aug 1, 2013

By Claudio Rocha Rosales

"Peñoles is a mining group with integrated operations for the smelting and refining of non-ferrous metals, and it is also a chemicals producer. Peñoles is the world’s foremost producer of refined silver, metallic bismuth and sodium sulphate. It is also the leading Latin American producer of refined gold, lead and zinc. The Met-Mex Peñoles Zinc Plant commenced operations in 1973 with an annual production capacity of 105,000 t/y zinc. Since then, production capacity has increased, and at present, it stands at 240,000 t/y zinc. In this paper, the leaching process and particularly the operation of the jarosite circuit is reviewed, specifying process improvements to treat high iron calcines.INTRODUCTIONTwenty years ago the Electrolytic Zinc Plant in Peñoles was treating high quality zinc concentrates with low concentrations of iron (~7.5 wt.%) and silica (1.8 wt.%). Nowadays the quality of zinc concentrates is poor with a typical iron content of around 11 wt.% and silica at 2.0 wt.%. This has created numerous processing problems in our roast-leach-purification- electrolysis sections. In order to meet customer requirements it is necessary to find processing solutions to assure the operational continuity of the plant. These processing solutions are the focal point of this paper.REVIEW OF THE LEACHING PROCESSThe purpose of the leaching process is to recover the metals, mainly zinc, through a series of extraction stages with sulphuric acid solutions, which progressively increases the zinc dissolution. After the series of acidification stages, the solution, which is rich in iron, is sent to the jarosite circuit to separate zinc from iron (Garcia & Valdez, 1996). The first step of the leaching process is the neutral leach circuit which produces a zinc sulphate solution that is sent to the purification section for the removal of impurities such as cadmium, cobalt and copper. Then this solution is sent to the tank house to feed the electrolytic cells."

Jan 1, 2016

By C. R. Edwards

"Equity Silver Mines Limited owns and operates an open pit silver 111ine located 37 km southeast of Houston in the Omineca District of British Columbia, Figure l. The property is approximately 300 km west of Prince George and 417 km east of the Port of Prince Rupert. This is the largest silver mine in Canada and one of the five largest silver producers in the western world.Equity is a subsidiary of Placer Development Limited, which owns 70 of Equity's issued and outstanding Common Shares. Placer was responsible for financing and developing the property and now provides general management and administrative services.All mining is by open pit methods, using three 1600 P&H shovels, eight 45 t Caterpillar and three 77 t Wabco trucks, three 40R rotary drills, two D8 dozers, one 9888 front-end loader and other ancillary equipment. We are now phasing out the Southern Tail pit and bringing the Main Zone into productior; see Figure 2.Comminution in the concentrator is achieved via primary, secondary, and tertiary crushers followed by rod and ball mills. The flotation circuit, with Southern Tail ore, produces a concentrate containing between 3 000 and 6 500 g of silver per tonne, 201 copper, and 25 g of gold per tonne. Running Main Zone ore, concentrate grades will decrease to about 4 500 g of silver per tonne, 17% copper, and 18 g of gold per tonne. Design milling capacity is 5 300 tpd, which is often exceeded.The flotation concentrate contains relatively high levels of antimony and arsenic. Because of these impurities Equity was unable to obtain economically acceptable long-term sales contracts for flotation concentrate. For this reason a leaching process was developed, and a plant designed, built and placed in operation. Due to the complex and unique technology involved, many start-up problems were encountered but by March 1983 the leach plant was considered ""fully operational."" This paper describes some of our progress and problems in bringing the Equity leach plant through its start-up period."

Jan 1, 1984

By T. W. Bingay

The production of both lead and zinc in Canada has steadily increased during recent years until today Canada ranks among the world's leading producers of both of these metals. The high prices which they have commanded have led to an energetic search for new deposits and also to an investigation of abandoned properties which, under the present conditions of better prices and more efficient methods of treatment, offer chances of commercial success. It is confidently expected that during the next few years success in both these lines of activity will further increase Canada's lead and zinc output, giving her a still higher ranking among the world's producers. In 1926, approximately 140,000 tons of metallic lead was produced from ores mined in Canada, and of this, 125,000 tons was refined in Canada at Tadanac, B.C. During the same year the production of metallic zinc from Canadian ores amounted to 68,000 tons, of which 62,000 tons was refined at Tadanac. History Of Lead and Zinc in Canada The production of lead in Canada is much older than that of zinc. The chief source has always been the interior of British Columbia. As earl y as the 'eighteen twenties', Indians and Hudson's Bay Company's trappers had discovered an outcrop of lead ore on the site of the present Blue Bell mine on the east shore of Kootenay lake, but it was not until1865 that active prospecting for lode deposits began. In the early nineties the activity of the silver-lead-zinc region of the Slocan reached its culmination and a steady production has been maintained down to the present time. Up to the end of 1924 the Slocan area produced over 38 million ounces of silver, nearly 300 million pounds of lead, and almost 122 million pounds of zinc.

Jan 1, 1927

By M. P. Amsden

"Ecstall Mining is a wholly-owned subsidiary of Texas Gulf Sulphur at Timmins, Ontario. The mill tonnage is 10,000 tons per day of two different ores, a copper zinc ore and a silver lead zinc ore, producing about 2400 tons of concentrates per day. These are as a copper concentrate, a high silver zinc concentrate, a low silver zinc concentrate and a silver-lead concentrate. For flotation recovery a very fine grind is required, about 80% minus 325 mesh and the concentrates produced are 40% minus 10 microns.The thickened concentrates are pumped to the filter floor for filtering and drying. The filtering and drying section is separated from the flotation section by a wall and is controlled from a dryer control room by one operator.Two operating panels are located in this control room. One contains stop-start controls for the thickeners, filter motors and vacuum pump motors, and stop-start controls for dryer feed conveyors and dryer product conveyors to concentrate load-out bins, as well as ammeters for conveyor drive motors. Dryer throughput is regulated by Merrick Type L weightometers located on the dryer discharge conveyors and recorded on tons per hour strip charts.The second panel contains the temperature strip charts, furnace drive ammeters, scrubber and exhaust gas controls, burner controls and panel alarms for the four dryers.Filtered concentrates are dried in Nichols-Herreshoff, multiple hearth, dryers consisting of nine hearths (zinc) and seven hearths (copper and lead). There are two dryers for handling zinc concentrates and one each for copper and lead concentrates. The dryers are heated by burning natural gas. Each zinc dryer handles 1,000 t.p.d. and the copper and lead dryers 750 t.p.d. each.Multiple hearth dryers are unusual in the base metal mining industry and the reasons for selecting them in preference to rotary dryers are as follows:1) The concentrates could only be filtered to 15 to 17 percent moisture. These sloppy filter cakes would be extremely difficult to handle in rotary dryers."

Jan 1, 1972

By M. S. Diederichs, G. Walton

"Developments in understanding the brittle fracture of rock over the past two decades ultimately led to the acceptance of a cohesion-weakening-friction-strengthening model as an appropriate strategy for the modelling of spalling using a continuum approach. This strength model has been used to replicate observed failure depths and geometries for a number of case studies in the literature, most notably the AECL Underground Research Laboratory in Manitoba. One thing which these case studies typically ignore, however, is the influence of rock dilatancy on the evolution of brittle failure. Physically, this phenomenon is the volumetric expansion of the rock due to fracture opening; numerically, this phenomenon is captured by the flow rule, which is often characterized by the dilation angle, ?. Accurately modelling rock dilatancy in conjunction with strength evolution is necessary both to predict the magnitude and distribution of ground displacements, as well as the exact depth and shape of the fracturing zone. Both of these factors can have significant implications for support design. This paper is focussed on presenting some of the recent developments in this field in the context of a number of numerical modelling case studies. Initially, a new model for the dilatancy of brittle rock is presented, as well as some representative data and model parameters for different rock types. Next, several case studies of highly stressed tunnels and shafts are presented. The results of continuum numerical models are presented to demonstrate the ability of the back analyses to match observed in-situ measurements and obtained. The predictive capabilities of the material model are also highlighted for cases where sufficient “a priori” information (such as laboratory compression testing data) are available. The issues of model nonuniqueness and strain-localization/bifurcation are also addressed."

Jan 1, 2015

By Mengsu Hu, Yuan Wang, Jonny Rutqvist

Material interfaces and typical boundary conditions are boundaries influencing the existence, uniqueness and stability of numerical solutions of water flow in heterogeneous media. The Numerical Manifold Method (NMM) with a two-cover-meshing system is an ideal method to handle boundaries, considering its flexibility with no need to adjust mathematical nodes onto boundaries, the meshing efficiency, and its integration precision. In this study, we derive and compare two new approaches for boundary constraints, i.e., a discontinuous approach with Lagrange multiplier and a continuous approach with jump function in the frame of NMM. In the discontinuous Lagrange multiplier method (LMM), Dirichlet boundaries or the material interfaces are regarded as discontinuities which are linked by Lagrange multipliers. In the continuous Jump function method (JFM), the material interfaces are regarded as inner interfaces, where the refraction law is realized by constructing jump terms with discontinuity of hydraulic gradient in its normal direction. Both the continuous and discontinuous approaches make full use of the aforementioned advantages of NMM and are established based on a clear physical meaning of water flow by our energy-work seepage model. The newly derived boundary-constraint approaches were coded into an NMM water flow model and tested for precision and efficiency on different simulation examples. We first tested both LMM and JFM for an idealized heterogeneous model, comparing the numerical results with analytical solutions. Then we tested both approaches with a heterogeneous model and compared the results of hydraulic head and specific discharge. We proved that both approaches are very suitable for material boundaries considering the accurate realization of the boundary constraints and the flexibility with no need for mesh-conforming.

Jan 1, 2015