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By M. Sutherland

"Increased efforts to improve mine safety have led to various successful forms of ground control in Canadian underground mines. At Inca Limited's T-3 Mine in Thompson, Manitoba, a perimeter blasting method has been implemented in jumbo drilled development headings.The technique utilizes an increased number of perimeter blast holes in the drill pattern while decreasing the linear charge density of explosives in any individual perimeter hole. The decrease in perimeter charge density means less blast damage to the surrounding structure.The benefits realized include increased safety through less loose ground and substantially less scaling time, less overbreak and improved long-term drift stability. This paper highlights the development and implementation of the perimeter blasting program.IntroductionThompson Mine Thompson Mine is a 6000 ton per day underground nickel mine located just outside the city of Thompson, 400 miles north of Winnipeg. The mine is serviced by the T-I shaft and by the T-3 shaft. The shafts are 10 000 ft apart and are connected on several levels with the deepest operating levels at T-1 and T-3 being 4000 ft and 2400 ft respectively.The T-3 Mine presently produces 52% of the total Thompson Mine production and 65070 of the 3000 ft of mine development each month. Current development of the 5 million ton 1, C orebody below 2400 level at T-3 will maintain these production and development ratios.Depending on equipment requirements, development headings at T-3 Mine vary in size. The 1, C ramp, at 17 1/2 ft wide by 10 1/2 ft high, is presently the largest development heading at T-3. Fifty- two per cent of the development footage is done with four Gardner Denver two boom electric /hydraulic jumbos and one Gardner Denver one boom electric /hydraulic jumbo. The remaining 48% is driven with hand-held jack-leg drills."

Jan 1, 1990

By George Langford

Introduction The manufacture of ductile beryllium is one of the most interesting problems confronting the metallurgist today, and one which becomes more acutely in need of resolution as the uses for beryllium increase. Beryllium belongs to the hexagonal group of metals along with zinc, magnesium, and cadmium. The melting point of the metal is about l,280°C. ± 5°C. Due to its brittleness, the metal's chief use is as an alloying agent in copper and iron. The very low absorption coefficient of beryllium for x-rays makes the metal ideal for x-ray windows, and, similarly, because of its low capture cross-section for neutrons, the metal holds a preferred position in the field of nuclear physics. Modern x-ray diffraction methods were responsible for explaining the mechanism whereby zinc metal, although brittle when cast, could be made ductile at room temperature. The diffraction patterns of zinc and magnesium indicated the importance of the parts played by recrystallization and preferred orientation in this mechanism. It was with this in mind that an Investigation into the recrystallization and preferred orientation of beryllium was undertaken. The investigation, after a series of experiments were conducted involving cold-working and annealing, yielded the recrystallization temperature curve for beryllium. Both the texture of preferred orientation and the effect of recrystallization on this texture when subjected to compressive stresses were also determined. W. A. Alexander, J. K. Swinton and L. M. Pidgeon, in their investigation on The Recrystallization Temperature of Beryllium (C.I.M., Trans., Vol. L, 1947, pp. 657-664), utilized the Brinell ball as a means of cold straining the metal. Sufficient strain was developed to estimate the recrystallization curve for the metal. However, in order to determine the lowest recrystallization curve, as well as to develop a preferred orientation structure, larger deformation than that possible with a Brinell ball was required. The plastic deformation of beryllium can be carried out at an elevated temperature above 700°C. Above 850°C., the metal is quite ductile and can be readily compressed or extruded.

Jan 1, 1948

By C. K. Baxter, A. Odeshi, M. Mohammadi, E. D. Cyr

"Metal additive manufacturing has been a revolutionary step in designing new complex shapes with faster and cleaner building capacity in comparison to subtractive manufacturing processes. The ability to print lightweight alloys such as aluminum has made metal 3D printing attractive to different industrial sector from aerospace to energy and bioengineering. Of particular interest in this study, are the mechanical and microstructural properties of AlSi10Mg-200°C alloys. In this project, samples were 3D-printed in horizontal direction using an EOS M290 machine by Direct Metal Laser Sintering (DMLS) technique. Uniaxial tensile tests and high strain-rate impact e tests were carried out to investigate the mechanical properties and to study the repeatability of the process. A constitutive model is developed to predict the results of the mechanical tests at varying strain rates to better understand the high strain-rate behaviour of these alloys. Using optical microscopy, features such as scan tracks and melt pools within the AlSi10Mg-200°C samples were observed, and the microstructure was observed to be homogenous. The previously listed tests were compared to the results obtained for similar cast alloy counterpart, i.e. A360.0.INTRODUCTION A relatively new way of manufacturing parts is on the increase as rapid prototyping becomes increasingly popular throughout the world. Additive manufacturing is a process which, given a 3D model, uses metallic material in powder form to build a part layer by layer until completion (Gu, Meiners, Wissenbach, & Poprawe, 2013). This way of rapid prototyping is very attractive in comparison to other possibilities because of its ability to accommodate complex design and geometries. Conventional manufacturing methods have limitations when it comes to complex geometries, but additive manufacturing allows for increased design flexibilities while maintaining a light and stable final product (Murr et al., 2012). It also allows for a reasonable cost, especially for small batch sizes that would otherwise be extremely expensive."

Jan 1, 2018

By L. C. So, S. Faucher, S. Mostaghel, A. Triwahyuono, D. Sauter, S. -Y. Oh, S. K. Lee, K. Aswin

"Molten hauling and water granulation are the commonly used slag treatment methods in the production of nickel. Water is present in these processes either to accelerate cooling of the dumped slag or in the granulation itself which creates an inherent safety risk of explosions. Even good design and operation are not sufficient to prevent explosions or injuries from occurring. Several dry methods to treat slags have been intensely studied. However, most of these technologies have never been commercialized due to numerous challenges including scalability, cost, low heat recovery efficiencies, and difficulties in heat utilization. Ecomaister-Hatch has recently developed and commercialized a reliable and simple Dry Atomization process, which eliminates water and allows for heat recovery. As part of the development towards other sectors, laboratory-scale and pilot-scale trials have been completed in a number of base metals and PGM facilities. Recently, Dry Atomization of a nickel laterite slag was successfully demonstrated at the laboratory-scale. The current paper introduces the technology and reports the test results obtained from atomization of the nickel slag.INTRODUCTION The processing of nickel laterites produces vast amounts of slag with over 90% of the feed to the furnace reporting as slag. Slag handing is therefore of critical importance to a laterite smelter. Traditionally there are two ways in which the slag is handled (1) Molten hauling, dumping, cooling and quarrying (2) Water granulation, dewatering, stockpiling. There are inherent disadvantages of both methods that will be outlined in this paper. An alternate route of Dry Atomization provides distinct advantages over the two conventional routes that are of particular interest to the nickel producer such as elimination of molten hauling, dumping and quarrying, elimination of water and improved safety. There is also the potential to convert the slag, which is typically regarded as a waste product, into a value added product and the continuous nature of slag tapping makes it amenable to heat recovery. Hatch has recently conducted laboratory-scale test work on laterite slag to demonstrate its viability for Dry Atomization. Results of this work are presented."

Jan 1, 2017

By W. Cholewa, T. S. Golosinski, J. Wedzicha

"Power requirements of belt conveyor drives are usually estimated based on the calculated belt tension which equals the sum of unit resistances to motion which the belt has to overcome. In most situations, the value of various unit resistances can be accurately predicted using published information (5,6,8,12). A simpler approach calls for use of standard formula and tabulated values of related factors which reflect various features of both the conveyor and the transported material (2,3,7) . None of these approaches is reliable when materials with unique properties are conveyed, nor if applied to conveyors working in extreme climatic conditions. Such is the case of oil sand mines in northern Alberta.There the bitumen content of oil sand causes it to behave in a unique manner. Furthermore the conveyors operate year around, with winter temperatures often lower than - 40°C. It was the objective of presented investigations to quantify the power requirements of conveyors, and related resistance to motion for the conveyors used in oil sand mines during winter operations.The other objective was to quantify the drive power requirements of oil sand conveyors during start-up. These requirements are usually much higher than those during norm al operation, and their quantification is of paramount importance for operation of large conveyors."

Jan 1, 1992

By F. Nava-Alonso, E. Pérez-García, A. Uribe-Salas, J. C. Fuentes-Aceituno, A. A. González-Ibarra, E. N. Castillo-Ventureño

"Precious metals cannot easily be recovered from tellurides by the standard cyanidation process. This work assesses the cyanidation of synthetic samples of precious metals tellurides and explores some alternatives for the leaching of these species (i.e. cyanidation in presence of lead nitrate and thiosulfate leaching). For this purpose, three chemical systems were studied: (1) cyanidation of silver telluride and the effect of lead (II) nitrate addition, (2) cyanidation at high alkalinity and high cyanide concentration of a gold-gold telluride sample containing tellurium and tellurium dioxide, and (3) thiosulfate leaching of silver telluride employing cupric sulfate as oxidant and EDTA as complexing agent for copper. Results showed that standard cyanidation dissolves 10.5% of silver from silver telluride in six hours, while with the addition of 100 mg/L lead increased the silver dissolution up to 100% in the same time. The standard cyanidation of the gold-gold telluride sample dissolves only metallic gold in six hours, while when cyanide concentration and pH were increased, gold and gold telluride were simultaneously dissolved. Finally, thiosulfate leaching dissolves 43.1% of silver from silver telluride in six hours.INTRODUCTION Precious metals tellurides are classified as refractory ores due to the difficulties associated with processing them by the standard cyanidation method. The increasing presence of gold/silver tellurides in some deposits around the world, specifically in Sonora, Mexico, requires new approaches to the cyanidation process, or the development of new leaching techniques. Treatments have been proposed for the recovery of gold and silver from their tellurides, including roasting, preoxidation, cyanidation with lead nitrate, and the use of leaching agents other than cyanide (Zhang, et al., 2010; Ellis and Deschenes, 2016). This work presents preliminary results of three options to recover precious metals from pure tellurides: the cyanidation of gold telluride at high cyanide concentration and high alkalinity, the addition of lead nitrate to the standard cyanidation process, and the use of sodium thiosulfate as leaching reagent."

Jan 1, 2017

By D. Groenveld, M. Rozou

"Recent trends move towards automation, smart sensors, internet of things, powerful DCS, and more data. Are those trends already utilized in a real time production environment? Today operators still have to monitor several complex processes at the same time and predict their behavior based on an overwhelming amount of data available.The fact of the operator being overloaded and humans being unable to process multivariable problems shows the need of a tool merging essential data and providing consistent, sound decisions for long-term profitability.This paper shows a successful execution of ABB’s process improvement services in Aitik (Boliden SA), a copper mine located in Sweden. Soft sensors, fuzzy rule blocks and model predictive control were seamlessly integrated in the control system of the grinding area, resulting in proper control of mill loads and particle size without violation of any constraints.INTRODUCTIONDepending on the ore characteristics and the targeted plant capacity, the design of the grinding circuit may vary significantly. Typically, the circuit consists of several mills (rod, ball, SAG, AG) in series and/or parallel with a number of classifiers and sumps at appropriate locations. The goal of the grinding section is to reduce the ore particle size to a level that enables efficient separation between gangue and precious metals in the subsiding processing step. The trade-off between quality and quantity has to be made. It is also crucial to execute this process step at the lowest possible energy and grinding media consumption.An optimal grinding process controller must manage to maintain a given fresh feed level while keeping the product size within a given range without violating any constraints such as power, torque or load limits. To accomplish the aforementioned, it is necessary to manipulate the ore feed rate, water feed rate and the mill speed. The most significant disturbances adding another degree of complexity to this control problem are ore hardness and the amount of circulating load."

Jan 1, 2016

By Edouard Masengo

A long dyke will be constructed in a lake with rockfill placed by end dumping method. Its crest will be at elevation 521.5 m compared to the nominal lake level at 520 m. In the first portion, its height will vary from 1.5 m on a 35.1 m thick tailings layer to 18.3 m on about 0.5 m of tailings. In the second portion, the dyke will be built on native silty clay and will vary from 18.3 to 15.2 m in height. The tailings consist in stratified layers of fine-grained soils showing lateral and vertical segregation. The tailings are compressible and may develop excess pore water pressure on loading. The tailings overlie a thin layer of relatively soft native silty clay. The till beneath the silty clay is considered incompressible compared to the material above. After construction, as the tailings and silty clay consolidate, pore water pressures will dissipate and dyke stability will improve. Since dyke stability will increase with time, the primary concern is its stability during construction. As a result of construction activities, three potential modes of failure were identified and recommendations were provided regarding the measures that should be undertaken to increase dyke stability during construction.

May 1, 2003

By A. Scheltema Beduin, M. Kalisch, E. Floch, R. J. Dijkhuis, H. J. Oterdoom

In metallurgical copper production, the traditional aim is to increase recovery of copper to the maximum. SMS Siemag (SMS) has supplied numerous furnaces for this application. New targets are to make sure end of line products are as safe as possible with respect to health and environment, and to maximize raw material utilization. This means a for example a minimization of leachable metals in slag, so it can be safely used as a construction material, and either a targeted concentration or fixation of volatile compounds, such as arsenic. Currently, 2 process routes are generally applied for slag cleaning. The first is grinding followed by flotation, and the second is slag cleaning in an (electrical) furnace. Popularity of both options has fluctuated over the years, and currently the milling-flotation seems to be the more popular option. In this article some of the advantages and disadvantages of both methods are described, and especially how long term environmental policies could have an impact on the decision which process route to choose. Finally, this article will describe some of the developments SMS is working on in pyrometallurgical slag cleaning that could influence the direction for the design of the copper plant of the future.

Jan 1, 2014

Falling asleep at the wheel of a moving vehicle is not only dangerous but avoidable. It is implicated in up to 30% of all road fatalities in general and up to 65% of mining incidents involving haulage trucks. These types of crashes normally result in serious injury and/or fatality due to the lack of breaking that occurs. However, when a 300 tonne haul truck has a sleep related crash it is not only the safety of the driver that has a high price but also the commercial impact on the mines? productivity and efficiency. We have been developing our ASTiD technology which stands for the Advisory System for Tired Drivers to seamlessly integrate in to Modular Mining?s Dispatch system to provide real-time early warning fatigue risk management. The benefits being driver shift optimisation, sustained productivity and of course less accidents. By monitoring the drivers alertness levels in real-time using ASTID, the Dispatcher becomes empowered to make critical, management decisions that will ultimately prevent serious injury or loss of life and the driver gets to stop when he needs to and not just when he is supposed to. This paper shows how this integrated solutions works.

May 1, 2011

By T. Stergiou

An extensive research is being carried out on the shaft furnace operation in order to minimize down-times and reduce operational cost. The need to increase the scrap percentage on the charging mix, together with the need of cheaper spare parts has led to the investigation of alternative materials for the burner system on the shaft furnace. This system consists of a burner block and a flame holder. Traditionally these items are constructed either from SiC ? oxide bonded or SiC-nitride bonded. A lot of problems have been confronted over the past 8 years of operation. Usually, large cracks are formed on both flame holders and burner blocks. This resulted in leakage of combustion gases to the back of the lining and a quick erosion of it. Additionally, the burner blocks suffer from chemical erosion, due to the increased amount of scrap used in the charging mix and the presence of slag inside the furnace. Alternative materials such as stainless steel for the flame holder and alumina-chromia refractory for the burner block have been tested in terms of life-time and resistance on chemical erosion. Furthermore, additional changes have been made on the burner block design in order to alter the flame shape and improve the scrap melting operation.

Jan 1, 2007

By Jeffrey D. Smith, William G. Fahrenholtz, Jose M. Soto

Interactions between A356 aluminum (Al-Si alloy) and dense fused silica (FS) riser tubes used for low-pressure casting of aluminum alloys were evaluated using a sessile drop approach. The tubes have a short service life, but cost and thermal shock resistance make them an effective solution. The main problem encountered during use is the reaction of aluminum with silica to form alumina and silicon, which causes failure. Tests have been conducted on as-fired (uncoated) and modified (coated) tubes. Experiments were carried out in a horizontal furnace at 1225°C under argon to minimize the effect of the aluminum oxide on the interactions at the alloy-silica interface. Images of the drop were acquired and contact angle values were estimated for uncoated and coated samples, but no significant differences in the contact angles were observed. Scanning electron microscopy revealed the presence of cracks at the interface between the reaction zone and the unreacted silica. The presence of reaction products (silicon in the reacting alloy and aluminum in a reaction zone between the alloy and the unaffected silica) has been confirmed using energy dispersive spectroscopy. A two layer coating system was found to be effective in reducing penetration of the aluminum alloy.

Jan 1, 2004

By Par G. Jönsson, Joachim von Scheele, D. S. Sarma, Mukul Goyal

Dust from flue gas cleaning systems at iron and steel production is frequently considered as a waste problem, but it is actually a potential raw material source. By using a technology like the oxyfuel based OXYFINES technique, it can be melted into a suitable form. The product from this processing, however, needs to meet the requirements of a recyclable raw material, here particularly a top-charged blast furnace feed. The present work has been focused on characterization of the product produced from these dusts by OXYFINES technology. The investigation has been carried out on samples of processed dusts from a European integrated steel mill. It was done by means of chemical analysis, density measurement, light optical microscopy, X-ray diffraction, scanning electron microscopy combined with energy dispersive spectroscopy, and micro indention hardness measurement. Special attention was paid to the presence of zinc, an element that might be harmful while recycling the material (e.g., in a blast furnace). The results show that the product contains four different regions with different morphologies and properties in the material, which are discussed in detail. The overall conclusion is that by processing the dusts in this way, a raw material suitable for recycling in a blast furnace can be obtained.

Jan 1, 2004

By Timothy D. Dreger

In the spring of 2009, Suncor Energy Inc. technical personnel saw an opportunity to improve planning 0and mining of overburden material in order to address aggressive construction goals and increased mining complexity. By tying together current and historical equipment performance, geological model information, and material observation in the field new operating elevations for the shovels were developed. At the same time, methodology of recording and reporting overburden movement through the Modular Mining DISPATCH system was changed. The result of this first stage of improvements was an increase in construction-grade material available at the face. The personnel involved realized that other opportunities were available to build on the initial successes and establish processes that would stand up to attrition and experience levels. A cross-functional technical team was assembled to identify ways of further improving workflows around overburden mining. Some of the opportunities realized include greater alignment between planning, reporting and operations as well as development of reporting tools that help steward Mine Operations to the plan. All of which have resulted in Suncor meeting or beating its forecast overburden targets. The cross-functional technical team continues to seek out new and better ways of doing business so Suncor can continue to deliver on its commitment of outstanding performance and results.

May 1, 2011

By A. Jeffkins

Visibility is restricted when operating load haul dump vehicles resulting in a number of serious accidents in the Ontario Mining Industry. One of the leading causes of these accidents is the inability of the equipment operator to see clearly people, objects or hazards around the machine. Previous line of sight testing by the research team found specific machine characteristics were responsible for blind spots and impaired visibility. In order to identify feasible design modifications a computer simulation program, Classic JACK 3.1, was utilized. Program features include human factors analysis, which allows evaluation of line of sight and operator posture in order to decrease risk of musculoskeletal injury. Research within the virtual computer environment consisted of a Visibility Audit and a Target Audit in order to quantitatively determine how certain components of the LHD design affected the line of sight around the vehicle. Results indicate that modifying the LHD light brackets, engine profile, cab posts and other components will enhance visibility. The addition of cameras located on the front and rear of the vehicle were able to enhance the operator?s sight lines to previously obstructed areas. Modifications to seat height and the operators orientation both improved sightlines and decreased risk factors associated with back and neck musculoskeletal disorders.

May 1, 2003

By J. K. Van Beek

The Deep Underground Science and Engineering Laboratory (DUSEL) is a scientific facility that will be placed in the deeper reaches of the Homestake mine, Lead, SD. Our team of geologists and engineers is carrying out the first scientific project awarded to the site ? Towards a Transparent Earth. Taking advantage of the thousands of open exploratory and sand-line holes, we are installing the beginnings of a seismic observatory. Each installed station consists of a 3-D accelerometer package and a 1 nanoradian 2-D tilt meter. In order to allow for a variety of monitoring and characterization studies, the array instruments are sensitive over the frequency bandwidth of 0.2 - 1 KHz. Three, three component accelerometer stations are currently installed ? in a 140 m deep bore beneath the slurry pump house, and in 12 m deep bores on the 2000-foot level, 800 and 400 m from the Ross shaft. There is a tilt-meter installed at each 2000 level station. These installations are in 150 mm diameter sand-holes. From the currently installed tilt sensors we are investigating solid earth deformation as a response to tidal potential. The accelerometers are being used to locate and characterize events associated with mine dewatering and rehabilitation.

May 1, 2009

By Tyson C. Birkett

Initial indicator mineral sampling covering 425,000 square km of northern Quebec and subsequent follow-up of positive results convinced the Ashton ? SOQUEM joint venture to acquire mineral rights to 380,000 hectares prospective for diamond in late summer, 2000. Drilling in 2001 and 2002 identified eight kimberlitic bodies, all significantly diamondiferous. Commercial size stones (retained on a square mesh sieve with openings 0.85 mm) and encouraging grades have been returned by several bodies tested to date: The Renard bodies are formed by steep-sided breccia pipes with kimberlitic matrix surrounded by irregular outboard breccia zones within country rock. These bodies were emplaced in high-grade metamorphic rocks of the Superior Province of Archean age. Orthogneiss with lesser tonalite hosts the breccias, although regionally paragneiss is also present. Diatreme facies portions and nearby country rock are intruded by minor to major (Renard 1) amounts of hypabyssal-facies kimberlitic rock. Renard bodies are macrocrystic, with large olivine crystals set in a groundmass of olivine, phlogopite, monticellite, spinel, carbonate, apatite and serpentine. Proximity of various Renard bodies, with most in a core area of 0.5 square km will allow planning of an efficient mining operation. Geophysics, especially magnetic surveying, has contributed to identifying bodies of kimberlitic rock.

May 1, 2003

By Victor A. Sowa

"Abstract - In 1938, a body of goethite and hematite was discovered beneath Steep Rock Lake near Atikokan, northwestern Ontario. This was at the time the largest and richest undeveloped iron ore body in North America. Mining began in 1944, fast-tracked by the needs of World War II, and through 1979 produced 79 Mt of 56.5% Fe. Production required the diversion of the Seine River, draining of Steep Rock Lake, building of a railroad, and a 25-fold increase of the local population. The mining project, at the time, was the largest project of its type undertaken in Canada. The current concepts of sustainable mine development and mine closures have advanced considerably since the period of operation and closure of the Steep Rock mines, and those operations would probably not have met current expectations of sustainability. However, some of the post-closure aspects of the mines provide illustrations of components of sustainability, which could form part of a basis for a post-mining sustainable land use plan. It is concluded that some of these components were successful in meeting current expectations of sustainable use, and although some aspects are unique to the circumstances at the Steep Rock mines, others could be applicable at other mine sites."

Jan 1, 2003

By S. Kaushik

The control room in a mineral processing plant has become increasingly complicated with complex unit operations coupled with rapidly evolving systems of sensors and control. Even with significant automation, human intervention is required to counter various scenarios that play out every day. A typical control room operator must monitor over 300 individual points of data in order to ensure the safe and efficient operation of the plant. At the same time, the experience of the workforce is decreasing as operators retire and the new generation enters the concentrators. Global competition for skilled operators continues to be strong and the opportunity to apprentice has diminished. The challenge is to provide a skill foundation for the operators so that they can be effective in the concentrator in a timely and safe manner. Progressively, the industry is turning to dynamic simulation tied into the control system. The simulator environment operates behind the control system to emulate the plant operation, reacting as the plant would when a change is made. The operator drives the process, with realistic feedback, which enables learning in a safe environment. This paper will take the reader through a green-field case study and discuss the effectiveness of integrating an operator training simulator (OTS) on the operator’s learning curve.

Jan 1, 2014

By Chris J. Pritchard

Pumpable, two-component resins for anchoring rock bolts provides significant advantages over traditional cartridge resin and cement grout systems where fast and easily adaptable support is required for difficult ground conditions. Cartridge resin anchoring with rock bolts is often ineffective in oversized, fractured and washed-out holes. Cement grouting of cable bolts is frequently plagued with QA and QC issues related to the grouting process. Installation of cable bolts with resin injection techniques is routinely completed in cycle allowing blasting immediately after cable bolting. Xstrata Nickel has evaluated the Minova Resin Injection System since 2007. The Nickel Rim Mine and partner Minova have tested and validated the Resin Injection process for bolting procedures including Hollow Fiberglass Bolts, Rebar, Modified Cone Bolts and Cable Bolts. The resin injection process is adaptable to most bolting processes and equipment. Currently, Nickel Rim Mine use 2 resin injection products with different set times to grout deep cable bolts and development support in highly variable ground conditions. The product predictability and adaptability in application along with a high crew acceptance continues to make this support process part of an adaptable ground support system. Product consistency and quality significantly reduce the quality control concerns for ground support in highly variable ground conditions.

May 1, 2011