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By Euler De Souza

Backfilling in Canadian mines has been practised for close to 100 years and evidence anticipates the application of mine fill technology at an increasing rate during the foreseeable future. The evolution of backfill technology is closely related to the advancement of modern mining methods and the development of new backfill technology continues to evolve. The authors, after conducting extensive surveys of backfill practices in underground mines across Canada, have concluded that, because backfill operations employ large quantities of cement and experience large costs associated both with backfilling practice and cement use, opportunities exist for reducing backfill energy costs and enhancing the application of alternative cementing agents in backfill. Consequently, the authors have developed an alternate, equally effective and lower cost binder agent replacement for cement, and incorporated waste glass into the development of a lower cost backfill (glassfill). This paper presents the results of two design stages associated with the development of glassfill: strength development and flow performance. The advancement of this technology has reached a stage that should promote industrial implementation within the Canadian mining industry. A number of Canadian mining operations exhibit potential for plant optimization through possible binder source replacement, and might thus realize associated reductions in backfill and energy costs.

Apr 1, 2005

By Neil McMillan

"By any measure of common practice, Claude Resources' Seabee Gold Mine in Northern Saskatchewan should not now be operating. Not because reserves dwindled, or grade dropped or prices weakened or technical problems arose, but because a host of unimaginable other problems beset the project, any one of which would normally have led to the mine's failure.The success of the Seabee Mine, and it is extremely successful, is a story of the vision and blunt determination of two men. Neither is remarkable in his own right but each possesses the characteristics which were necessary to forge a highly productive and profitable narrow-vein mine in the midst of the most bizarre and unpredictable events which likely have ever beset a mine start-up in Canadian history.Together, Bill MacNeill, a Saskatchewan born, former bush pilot and Ray Gagnon, a big hearted, hard-fisted, miner with 44 years of experience in Canada's underground, built the Seabee Mine.They didn't accomplish this with brilliant geology, outstanding engineering or nimble corporate manouvering but rather a stubbornness and raw common sense which likely are all too often, ingredients missing in failed projects.The Seabee Mine is 100% owned by Claude Resources, a Saskatoon based company taken over by Bill MacNeill, its current chairman, in 1982. The company is listed on the TSE and produces 1200 barrels of oil per day and about 60,000 oz of gold per year. The company has a strong balance sheet, is very profitable and has 18 million shares outstanding.The Seabee property in Northern Saskatchewan started out like many other gold exploration properties in Canada.It was discovered in the l 940's by what is now Cominco, and, while highly regarded by that company the property sat largely dormant until acquired by Claude Resources in 1985.Claude did what most junior exploration companies would do and went looking for a company with a depth of expertise to joint venture the property.That company was Placer Development who could earn a 55% interest in the Seabee by delivering a bankable feasibility study on the Project by July 1988 and providing financing to production.Placer Development was an excellent company and spent over $8 million dollars on the Seabee over a 3 year period. Unfortunately for Claude Resources, Placer Development merged with Dorne Mines in 1987 and the new merged company, Placer Dome, established a minimum production threshold greater than the 50,000 oz per year which the Seabee appeared capable of supporting at that time. Placer Dome's request for an indefinite extension of the joint venture agreement to allow it to drill off a larger ore body was rejected by Claude Resources and the Seabee Property was returned to Claude in 1988."

Jan 1, 1998

By Andrea M. Ouchi

A major focus of ground control research presently being conducted by the Geomechanics Group in the University of British Columbia Mining Engineering Department is to incorporate weak rock masses (RMR76 less than 50) into existing empirical design relationships. An emphasis is being placed upon the updated span design curve/critical span graph originally developed at UBC. The original database has been augmented by mapping of one mine in Montana and of several mines within the Carlin and Getchell Trends of Nevada. In addition, a neural network analysis has been performed and modifications of the span design curves at the lower RMR76 range have been made. The common factor in all the above mentioned mines is a weak back and/or walls. In most cases, the ore zone is the weakest rock unit and must be dealt with to safely extract the mineral bearing rock. This work attempts to provide rock mechanic tools that will enable a mine operator to make economic decisions that will also ensure a safe working environment.

May 1, 2004

By Charles Kocsis

Over the last few years a multi-faceted feasibility study has been evaluating the introduction of hydrogen fuel cell powered equipment into underground mines to replaced diesel engine powered equipment. The analysis has shown that under normal operating conditions fuel cells could at the very least be an environmental and health benefit by eliminating combustion engines and their unwanted by-products. However, they could also generate significant reductions in the amount of ventilation a mine needs to supply when compared to dieselized operations; this would further decrease a mine?s energy consumption, its associated greenhouse gas impact and also reduce a mine?s significant ventilation associated costs. Fuel cell powered equipment also has the advantage of lower noise and heat production compared to their equivalent diesel powered counterpart. The degree to which fuel cells can generate ventilation benefits in underground mines depends upon a number of operational parameters and mine specific qualifiers such as current ventilation control or management, mine depth, inherent dust conditions and minimum velocity requirements. However another major consideration in the introduction of fuel cells in underground mines will be the safety requirements associated with diluting and removing the potentially explosive hydrogen in the event of a gas leak. In outside surface applications, it is possible to use dispersion, buoyancy, time, and lack of ignition sources as mitigating factors in deriving a low risk of an explosion. However, in underground operations these factors change, dispersion and buoyancy are limited; time may not be available and in non-coal mines ignition sources are not typically controlled. When a hydrogen leak occurs, the availability of sufficient ventilation to dilute and effectively remove the gas will be critical, consequently ventilation may be the prime risk controlling factor. In this paper, the authors evaluate the potential benefits of replacing diesel engines with fuel cells in powered production equipment, discuss the mitigating qualifiers that could limit ventilation savings and evaluate solutions to retain and maintain an additional ventilation capacity in the event of an emergency situation such as a hydrogen leak from the fuel cell stack or its distribution system.

May 1, 2007

By Phil Thwaites

"The mining industry uses many types of mineral and metallurgical plants to produce saleable product from ore mined. Plant design history has left current operations with a mixture of manual operation and various forms of automated process controls. Consequently, we typically see high variability in the continuous operations together with a shortfall in the attainment of full capacity, or higher utilization of consumables.At a level of best practice, “Operational Performance Excellence” focuses on process control, using automation and control systems to deliver process optimization. This more sophisticated delivery is a great deal more difficult than the first stage of equipment selection / installation. It includes the appropriate selection of the right instrumentation, control system, key process knowledge, individuals with a solid control engineering background/experience, and the essential backing/ support of the operations management team together leading to higher value delivery. Robust solutions can be realized, considerably minimizing process variation, thus leading to process optimization. This approach results in an easier, efficient and safer process while providing considerable returns for the plant owners.How variable are your processes, and do you maintain optimized process performance with dedicated resources, modern instrumentation, ‘best practice’ control systems and performance monitoring tools? In this lecture, these questions and their possible answers are discussed.357"

Jan 1, 2013

By James D. Bittner

Separation Technologies, LLC (ST) has developed a processing system based on triboelectric charging and electrostatic separation that provides the mineral processing industry a means to beneficiate fine materials with an entirely dry technology. The environmentally friendly process can eliminate wet processing and required drying of the final material. The process requires little if any pre-treatment of the material other than grinding and operates at high capacity ? up to 45 tonnes per hour by a compact machine. Energy consumption is low, approximately 1 kWh/tonnes of material processed. Since the only potential emission of the process is dust, permitting is typically relatively easy. In contrast to the other available electrostatic separation processes that are typically limited to particles greater than 75 µm in size, the ST belt separator is ideally suited for separation of very fine (<1 µm) to moderately coarse (500 µm) materials with very high throughputs. The triboelectric particle charging is effective for a wide range of materials and only requires particle ? particle contact. The small gap, high electric field, counter current flow, vigorous particle-particle agitation and self-cleaning action of the belt on the electrodes are the critical features of the ST separator. The high efficiency multi-stage separation through charging / recharging and internal recycle results in far superior separations and is effective on fine materials that cannot be separated at all by the conventional electrostatic techniques. Since 1995, this triboelectric process has been extensively used for the beneficiation of coal fly ash with eighteen separators in place and over 100 machine-years of operation at locations in the US and Europe. The technology has been also successfully applied to the beneficiation of a variety of minerals including calcium carbonates, talc, and potash.

Nov 1, 2011

By S. Stefanizzi

In the present paper, numerical simulations based on a finite/discrete element approach are used to study deformation and failure process during standard rock mechanics. FEM/DEM modeling has been used as available with the ELFEN code, which explicitly model the transition from continuum to discontinuum. The transition is simulated through a crack nucleation and propagation that obeys to the Griffith?s failure criterion. If the fracture criterion within the intact rock (represented by FEM) is met, a new crack (represented by DEM) is initiated. Remeshing allows the fracture process through the FEM mesh to be tracked and visualized, thus contact properties can be assigned to pre-existing fractures and newly generated fractures. In this study, compressive tests of rock samples are simulated. The applicability of ELFEN to properly and efficiently simulate typical laboratory rock mechanics tests, with reference to the rock fracture process, is described in detail. In addition, an indirect validation of the extensional strain criterion proposed by Stacey (1981) is given.

May 1, 2009

By Nicholas Macrae Steven

Abstract - The Shaba-type Luamata Cu-Co(-Ni) deposit (11°50_S, 24°28_E) is located in a tectonic slice of Katangan Roan Supergroup (Mines Group) sedimentary rocks, surrounded by younger Kundelungu Supergroup lithologies in the external fold and thrust belt of the Lufilian Arc. Luamata is a classic central African copper clearing in dense woodland, visible as a tonal botanical anomaly on Landsat imagery. Supergene Cu-Co mineralization (especially malachite and subordinate chalcocite, digenite, covellite, and copper and cobalt oxides) and, probably hypogene, bornite, and chalcopyrite are hosted by altered, but essentially unmetamorphosed, moderately dipping, dolostones and dolomitic shales. Alteration products include talcose dolomite, sericite rocks and intense silicification and brecciation. Friable yellow shale is best mineralized with cobalt (up to 0.43 wt%), whereas, highest copper grades occur in brecciated, silicified shale (up to 13.5 wt% CuO). Soil copper and cobalt contents are up to 2.2 and 0.6 wt%, respectively. A newly identified nickel zone (where soil contents exceed 0.1 wt% Ni) fringes the Cu-Co deposit. Polymictic, matrix-supported breccias with a calcareous matrix that underlie the Cu-Co deposit are interpreted to be fluidization breccias related to thrust tectonics and the emplacement of the Mines Group slice. Although small compared to the Kolwezi district Shaba deposits in the Democratic Republic of the Congo, Luamata exhibits all the classic features of an ore deposit type (with low calcite contents), whose high metal concentrations could potentially be very profitably exploited by low-cost opencast mining and hydrometallurgical recovery methods.

Jan 1, 2000

By R. C. Fernandes, F. L. Santos

Aluminum alloys in particular, have certain limitations when subjected to welding process. This is mainly present because aluminum alloys have high thermal conductivity, high contraction in solidification and high hydrogen solubility. Taking this into account, the FSW process has great potential for this application, since it is autogenous, held without metal melting and without the use of slags or shielding gases. From this concept, the aim of this study is to evaluate the joining of thin sheets of aluminum alloy 3105 H26 with 0.7 mm of thickness. To performing of the tests, some parameters were analyzed, such as: tool penetration in the sheets, attack angle, the type of welding tool and penetration control mode (position or force). The results indicated that the force control mode is most suitable for thin sheets, and the transient state at the beginning of welding was the most critical part to control the welding quality.

Jan 1, 2015

By M. E. Charles

The use of water flowing as a lower layer to reduce pressure gradients in petroleum pipelines was investigated using 17.5 deg. A.P.I. Lloydminster crude oil in a 1-inch laboratory pipe-line and a 21h-inch field pipeline. The method was found to be very effective in reducing the pressure gradient below that for the oil flowing alone. The factor by which the pres-sure gradient was reduced varied with the percentage of water added, and in general exceeded 10 for water contents ranging from 40 to 60 per cent. Within this range of water content the pressure gradient reduction factor was independent of the oil flow rate.

Jan 1, 1960

By M. J. Slater

Ion exchange using resins is one of the few processes capable of reducing ionic contaminants in effluents to very low levels. Continuous fluidized-bed ion exchange is an advantageous technique for processing dirty effluents and thin slurries. It also reduces resin inventory and equipment cost compared to fixed packed beds. A simple continuous fluidized-bed unit has been investigated for treating effluents and its performance is described. Breakthrough curves were first obtained from static fluidized fixed beds; these data were then used to determine the required operating conditions for a periodic-flow, countercurrent fluidized-bed ion exchange system. A waste stream, containing about 56 ppm copper, was treated in the continuous system using an extraction fluidized bed depth of 203 cm and a flow rate of 1.22 cm3/ cm2s (900 gph / sq.ft) to yield an effluent containing less than 0.02 ppm copper. A generalized design method is proposed for similar chemical systems.

Jan 1, 1978

By F. Hassani, R. Mikaeil, B. Ferdowsi

Two analytical solutions for estimating the ovaling deformation and forces in circular tunnels are widely used in engineering practice, due to soil-structure interaction under seismic loading. This paper discusses the discrepancy between the two analytical and finite difference methods. A comparison of the two analytical methods shows that the calculated forces and displacements are identical for the condition of full-slip between the tunnel lining and ground. However, the calculated lining thrusts differ by an order of magnitude when considering no-slip between the tunnel lining and the ground. The analytical solutions are compared to numerical analyses of the no-slip condition using the finite difference method to validate which of the two methods provide the correct method. To achieve the goal, numerical modelling, field data of the Kuhin railway tunnel and Manjil earthquake characteristics are used. Numerical analysis results agree with one of the analytical solutions that provides a higher estimate of the thrust on the tunnel lining, thus highlighting the limitation of the other analytical solution.

Jan 1, 2008

By Mohammad Noaparast, Babak Fotoohi

"Due to certain advantages in (semi-)Autogenous-Ball mill circuits in most of the high-throughput ore grinding units of mineral processing plants, much attention is paid to optimize the mill performance. Despite the maturity of the grinding mill mechanical design, there had been made less attention to the efficiency of the grinding media in the past. In this research, the possibility of establishing a relationship between liner/lifter wear rate and variations in the composition of the iron ore (from Chadormalu mine) is investigated.Measurements and determination of liner/lifter wear rates and patterns concluded in recognition of critical liner segments exposed to much abrasion during the ore grinding. After metallurgical analysis of liner materials and correlation of wear rate with the ore composition, the homogeneity in the metallurgical microstructure of the alloyed steel (such as the uniform distribution and amounts of the constituent phases) was determined as the most influential factor in the response of the liner/lifter to the variations in the ore composition. Magnetite with greater abrasion index than hematite, in finer particles, is responsible for additional abrasion of liners; hematite with greater work index exists in the mill with larger particle sizes, thus it could produce wear on liner parts with less tolerance to impact as is the situation for martensitic steels.INTRODUCTIONThe mineralization in Chadormalu plutonic iron ore deposit is consisted of mostly magnetite, hematite, martite, apatite, quartz and carbonates. The average composition of the ore is presented in Table 1. In the processing circuit, the gyratory crushed ore reduced to 30 cm would finally be the feed to three similar 32’ semi-autogenous mills in parallel processing lines. The pulp in the mill would have the characteristics mentioned in Table 2. The quality of the mill output has its direct effect on the downstream processes either physically or chemically (e.g. in cycloning or flotation respectively). In order to take advantage of optimum performance for these circuits, a close control of the ore grinding conditions is necessary; because any shortages in throughput, liner/lifter damage or changes in ore composition could bring the unexpected casualties. In this work, it has been attempted to find (possibly) a reasonable relationship between variations in ore characteristics together with liner quality and the amount of wear rate in different liner/lifter segments of a semi-autigenous mill. Liner/lifter segments are supplied by three different domestic steel making companies. The alloy structure of the liners/lifters is made up of pearlitic chromoly steel."

Jan 1, 2005

By A. C. Wilson

In 1991, local prospector C. ?Mickey? Clement recovered at least three alluvial diamonds from the Michipicoten River. Two of these stones were sent to the Department of Mineralogy, Royal Ontario Museum, where they were identified as industrial grade diamonds with weights of 1.05 and 1.13 carats. Both stones were described as frosted and graphite-inclusion riddled. In 1995, prospector Sandor Surmacz and geologist Marcelle Hauseux discovered diamonds in bedrock approximately 20 km north of the Michipicoten River. An 18.1-kg bulk sample of a xenolith-rich lamprophyre, taken from an outcrop at the side of the Trans Canada Highway north of Wawa, yielded 1 macro diamond and 5 micro diamonds. All but one was gem quality (Sage 2000). Since then, more than 36 occurrences of diamonds in bedrock have been reported in an approximately 30 km2 area centred 20 km north of the town of Wawa. The occurrences are hosted within a sequence of unusual, Archean-aged, heterolithic breccias previously considered to have no economic significance. Ten kimberlite occurrences also have been confirmed in the Michipicoten greenstone belt in the last 5 years. Two of these kimberlites are diamondiferous. To date, expenditures on property acquisition and diamond exploration in the Wawa are estimated at $120 million (CAN). This paper summarizes the geological observations made on these occurrences and discusses including the relationship between the occurrences and the regional geology.

May 1, 2003

By John L. Mero

"The ocean has served humanity as a source of raw materials for thousands of years, but only on a minimal scale relative to its potential. Exploration programs have shown the ocean to contain a large number of mineral deposits of great extent and attractive grade. Recent research has indicated that a number of these deposits can be economically exploited with present-day technology and that the cost of winning many industrially important minerals from the oceanic deposits is potentially much less than that of winning similar minerals from land deposits. Although the finding of mineral deposits in the sea is a relatively simple matter at the present time, the exploitation of many of these deposits has lagged due to the lack of the availability of specific mining techniques for the individual deposits. Within the past two years, however, several developments have taken place in the design and testing of ocean mining systems in depths of water as great as 12,000 feet which indicate that the problem of mining in the ocean may soon be solved.Within the next decade, the ocean should prove to be a major source of many minerals for society and should come to dominate as a source of such metals as copper, nickel, cobalt, manganese, etc. Within a few years of the initiation of the mining of the deep-sea metalliferous nodules, land sources of such metals as nickel, cobalt, copper, manganese, etc. will be seriously affected and it is conceivable that the present structure of the world mining industry will undergo a substantial change in character."

Jan 1, 1972

By D. W. Euler, D. G. Brophey

"In an attempt to address the issue of rising labour costs, and to improve productivity, a laser-based system to guide underground LHDs and trucks has been developed. This comprehensive system is known as the Opti-Trak system.Essentially, the vehicle is equipped with front and rear-mounted lasers which scan a reference strip mounted on the drift back. The vehicle follows this reference strip and in addition, based on reflective bar codes mounted beside the reference strip, initiates certain functions (i.e. dump cycle, speed change, brake check, etc.). Any programming that is drift-specific is handled by the positioning of the reference strips and bar codes. Consequently, the vehicle can easily travel to many different haulageways or branches, providing the reference strip and bar codes are in place.The advantages of this system are an immediate elimination of haulage operator costs and an increase in available hauling time to 7 hours out of an 8-hour shift as compared to the typical 5Y2 out of 8 hours that a manned haulage system offers.This paper describes the Opti-Trak system and the benefits to be realized from automation of mine haulage requirements."

Jan 1, 1994

By R. Venugopal, Saxena. V. K., U. Sankrityayan

"There is a dire need of a technology which can break the mineral interfaces to enhance liberation with minimum energy consumption in mineral beneficiation processes. Understanding of mineral crystal system and interfaces is essential to develop such methodology. So, this study is carried out to find out the role of mineral crystallography in milling and liberation. Data related of mineral crystallography, Vickers Hardness Number, Bond Work Index and beneficiation processes were collected from literature and detailed statistical analysis has been carried out to establish a correlation among these parameters. It was found that atomic weight and cell parameters shown statistically significant relationship with Vickers Hardness Number of minerals, which controls the milling characteristics of ores. Liberation characteristics of five different kinds of ores were analyzed considering the types of interfaces between valuable and gangue minerals. It was found that phase interfaces play vita role in liberation and coarser liberation can be achieved in the minerals of incoherent crystal systems like manganese and zinc ores. Study of this subject can help us to understand the effect of stress wave propagation in solids and its effect on crystal interfaces. It can also help us to design a technology of future to break the mineral interfaces.INTRODUCTIONCommunition is energy intensive mineral processing operation and consumes up to 2% of the total electric power generated in the world. Energy consumption due to comminution is increasing every year as there is growing needs to exploit lower grade ore bodies and process rejects (Blazy et al., 1994; DOE, 2005). Low grade ores require crushing and grinding to liberate the valuable minerals which are further separated from gangues by various beneficiation methods like gravity separation, floatation, leaching etc. Currently, comminution methods are selected based on the reduction ratio and energy consumption but effect of grinding methods on subsequent processing methods specially on liberation also need to be studied to optimize the entire beneficiation process. Most of the attempts made in past to minimize the energy consumption in milling to enhance the mineral liberation were focused on compression mechanism, chemical additives, thermal treatment, microwave treatment and electric disintegration (Kilpelm and Austin, 1982; Norgate and Weller et al, 1994; Bearman et al., 1997; Kumar et al., 2010; Wang el al., 2011; Singh et al., 2012). But the role of mineral crystallography on milling and liberation behavior of minerals not fully explored yet."

Jan 1, 2013

By E. Bongajum

We present results from petrophysical studies to characterize a Zn-Pb-Ag deposit in Nash Creek, New Brunswick. The measurements are part of an integrated study that includes geological and geophysical data acquired on the property. In order to successfully characterize the ore body, an understanding of the relevant physical parameters and their change with vertical and lateral variations of the target lithology is necessary. The quality of the estimated 3D variation in the physical properties is supported by the presence of several boreholes that randomly span the survey region. Density was measured from cores of thirty-two boreholes across the area. Seventeen of these boreholes constitute two intersecting borehole profiles, which is ideal for locally modeling the 3D distribution of the ore deposit. High densities (>3.2g/cm3) correlate strongly with Zn-rich mineralization zones (low resistivity). Compression and shear wave velocity measurements made from representative core samples of the regional geology range from ~2.91 to ~6.41 km/s for P-waves and from ~1.41 to ~4.20 km/s for S-waves. The lower bounds of these velocity values correspond to regions with a high degree of alteration. Moreover, porosity estimates from rocks on the property suggest that porosities range from 0.35% to 11.79%. Induced polarization (IP) measurements confirm that mineralized samples show a significant chargeability and resistivity contrast with respect to the host rock. Thus, chargeability and resistivity information can be combined to adequately identify conductors associated with mineralization in electrical survey data. Information on these physical parameters and their 3D statistical distribution have serious implications on various aspects of mineral exploration that include: resource estimation, choice of geophysical data acquisition and interpretation, and information for preliminary rock stability assessment.

May 1, 2009

By Lian-Jin Tao

With fast development of China modernization, road construction obtains great achievement. However, in the construction process of highway, especially the high-grade highway in mountainous area, there are many unavoidable high cut slopes. Specifications for Design of Highway Subgrades, China, prescribe that the design scheme of slope with height more than 30m should be compared with bridge scheme and tunnel scheme economically. In spite of the existing guidelines, it is still quite common to see many high slopes due to engineering geological conditions, highway line shape, cost and issues related to traditional design ideas. Actually the traditional way with ?high backfill, the high cut? for mountainous highways seriously damages the original ecological environment and groundwater system, especially to those area with weak ecology, where the damage is unrecoverable. It is quite common practice to use artificial vegetation for cut slope virescence, however it still has problems such as low ratio of survivor, high maintenance cost and lack of species diversity. Now people are more and more aware of the importance of ecological environment, it becomes urgent to decrease the damage to ecological environment after ensuring the stability of high slopes. With the aim to reduce ecological damage, we proposed a new design approach which is ecological environment friendly by decreasing cut slope height with steep excavation scheme. This approach requires that (1) the geological condition is good, and the rockmass can be sTable itself; (2) excavation should not badly damage the rock, which means blasting must be controled by using buffer blasting, smooth blasting and pre-splitting blasting; (3) if local geological condition is not very good, excavation should have intervals for one bench, the advised space is 20m; (4) to ensure the slope stability in construction process, the cut slope should be reinforced more strongly than usual and in time. Finally, the deformation of the slope and the working condition of the reinforcement structure should be monitored to ensure the slope stability. The new design is used to a roadside cut slope of provincial trunk highway S223 in Guangdong Province. Based on intensive geological investigation and borehole tests, it is found that the slope rock mass is intact and sound, and the rock strength is quite high. Results from numerical modeling by UDEC reveal that compared with the traditional design scheme with 90.23m high slope, the steep scheme with only 23.46m high is characterized by its relatively large deformation and stress concentration, however the influenced area only appears at the upper slope and tends to sTable. With cable reinforcement, the stability of slope excavated steeply can be guaranteed. Deformation of the slope and the cable force are monitored in details in the period of construction, which show that the deformation of the slope decreases gradually and the final deformation is very small, and the cable tensions change small after the cables were tensioned. It is optimistically estimated that the steep slope should be sTable during operation. Comparison analysis between the steep scheme and the common scheme affirms that the steep excavation is better than the traditional scheme in terms of ecological environmental effect, slope height, the excavated amount, the excavated quantity of slope surface, engineering cost. It is concluded that if geological condition permits, the steep cut scheme should be used with better benefits.

May 1, 2009

By Š. Šachlová, T. Lokajícek, M. Petružálek, T. Svitek, A. Štastná

During the past 20 years, alkali silicate reaction (ASR) as a cause of concrete deterioration has been studied by a wide range of experimental methods such as microstructural and macrostructural analysis, bulk chemical analysis, X-ray and neutron diffraction analysis, etc. All of these data are compared with expansion values of mortar bars (following ASTM standard C 1260). Recent studies indicate the useful application of non-destructive methods with the aim of better reflecting mechanical properties and the degree of deterioration of real concrete. Ultrasonic testing methods (including ultrasonic pulse velocity UPV) are widely used to determine material mechanical properties and the changes induced by a variety of mechanical or chemical processes. However, only a few laboratory studies of ASR focused on ultrasonic testing of mortar bars. Due to this fact, a heating chamber was designed and constructed to enable ultrasonic sounding of mortar bar specimens while stored in accelerating solution. Regular ultrasonic sounding of mortar bars reveals significant dependence of ultrasonic data such as longitudinal P-wave velocity, signal energy, signal amplitude and signal frequency on mortar bar storage time. Ultrasonic data were subjected to time domain as well as frequency domain analysis. Different storage conditions were used to determine the effect of ASR on ultrasonic parameters. Mortar bars, prepared in the same manner with one type of aggregate, were stored in cold or warm water or in an accelerating warm medium. Ultrasonic data accurately reflects the differences in hardening and deterioration of tested mortar bars due to different storage conditions. Ultrasonic results showed very good correlation with the results of ASTM standard expansion tests and much higher sensitivity to ASR-induced concrete deterioration. Expansion tests showed 1% measured length differences in comparison with up to 80% resolution of ultrasonic data. The ultrasonic testing proved to be a suitable laboratory method for investigating ASR-related processes and could lead to an improvement of standard testing procedures.

Jan 1, 2015