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By N K. DavT, A Coggan

The performance of in situ, shallow water covers in controlling acid generation was evaluated at four recently decommissioned pyritic uranium tailings sites at Elliot Lake, Ontario, Canada. The tailings are acid generating, having a pyrite content of approximately five to ten per cent and a very low to non-existent alkaline buffering capacity. Adverse market conditions led to the closure of all operating uranium mines in the early- to mid-1990s, followed by rehabilitation and decommissioning of mine and waste management facilities. In order to control acidic drainage, all new and active tailings areas at Denison, Quirke, Panel, Spanish-American and Stanleigh mine sites were re-engineered to provide in situ submersion of these tailings under shallow water covers. The tailings impoundment dams were upgraded and reinforced or in some cases reconstructed, to minimise seepages and provide a minimum 1 m depth of water cover. With the exception of Stanleigh mine, which was closed in 1996 and rehabilitated during the late-1990s, the water covered Tailings Management Areas (TMAs) at other sites have been in operation for a period of six to nine years. The surface water quality at these sites is maintained at near neutral pH conditions by periodic addition of lime slurry to the established water covers. Additional treatment of effluent is provided as required to meet the discharge water quality standards. The performance of the established water covers at the sites was evaluated by analysing the annual equivalent limestone consumption data. The results were compared with the performance of an older, decommissioned Nordic TMA, which was rehabilitated using revegetation techniques. The water covers at these sites are performing as designed and acid generation has been reduced to low levels. Based on the total amount of yearly equivalent limestone required to maintain water quality in the water cover and at the effluent treatment plant, it is concluded that acid generation rate at the Denison TMA has reduced to less than 0.15 per cent of its pre-water cover conditions during normal operation and rehabilitation periods. In comparison to the revegetated Nordic TMA, the acid generation rates at Denison and Panel TMAs have decreased to less than 1.6 per cent of that at the Nordic TMA. The acid generation rate at the Quirke TMA was comparable or only slightly lower than that at the Nordic TMA because of its unique terraced cell configuration, having tailings in five hydraulically interconnected cells at different elevations. Historic acidity and oxidation reaction products, accumulated during normal operating and pre-water cover periods, are flushing from upstream locations to downstream cells, thus requiring much higher equivalent limestone additions for acid neutralisation and effluent treatment.

Jan 1, 2003

By P. Kiruthika, A. Murali Krishna

Soil liquefaction is a dangerous phenomenon that involves huge damages during strong earthquake ground motion event. Stone columns (SCs) are widely used as liquefaction mitigation element which is expected to perform the improvements against liquefaction hazard by densifying, increasing the stiffness and rapid dissipation of excess pore water pressure in the surrounding soil. Although in the recent times few studies on the behaviour of stone columns in the seismic zone has evolved, the performance of SCs in the multi-layered soils is not extensively examined. This paper presents the numerical investigations on the performance of SCs installed in the multi-layered soils as a liquefaction mitigation measure against the seismic loading. The acceleration time histories, Excess Porewater Pressure (EPP), vertical displacement and stress ratio evaluated along different depths using PLAXIS 2D. With the installation of stone column there is a considerable reduction in the acceleration amplitude, which in turn reduces the EPP and vertical displacement at different locations and the amplitude of reduction depends on the soil stiffness levels at the depth.

Sep 1, 2022

By Akhila Manne, Prasad P. V S R

Storage tanks are heavily loaded thin-shelled structures that exert large loads on and require large foundations to support them. They are generally very sensitive to foundation settlements as it may hinder the performance of tanks resulting in significant commercial or social impacts. Selection of their foundation is dependent on availability of suitable ground and limitations imposed by design specifications. Design of the tank foundations is generally based on theoretical methods and validation by representative field tests. This paper reviews settlement criteria for storage tanks as per national and international standards, case studies of large to medium diameter tanks supported on deep foundation i.e., bored cast-in-situ piles and shallow foundations on improved ground and their performance during load tests & hydro-tests is discussed. Paper concludes that storage tanks can also be supported on shallow foundations resting on improved ground reducing the settlement, time and cost significantly depending on the sub-soil.

Nov 1, 2022

By D. M. Urich

This paper is a follow-up on a previous paper presented at the A.I.M.E. Meeting in Chicago, Illinois, on February 17, 1965, by Mr. D. Kelly Campbell. Mr. Campbell's paper was presented prior to the operation of the Eveleth Taconite-Company's Plant, and this paper outlines and reports on the operation and performance of the Plant after the first nineteen months of operation.

Jan 1, 1967

By M Gao

Six new IsaMills were installed for the George Fisher flowsheet in the Lead/Zinc Concentrator of Mount Isa Mines to produce a product P80 as fine as seven microns. The objective was better liberation of galena and sphalerite. The IsaMill commissioning was completed by the end of 1999. The six new IsaMills were running to the metallurgical specifications almost immediately after start-up. This paper reports the performance of the George Fisher IsaMills in the zinc circuits and some of the latest development in the IsaMill designs and maintenance during George Fisher commissioning.

Jan 1, 2000

By Bruno Bussière, Michel Aubertin, Anne-Marie Dagenais, Johanne Cyr

A five steps remediation program was commissioned in 1998 for the acid generating Lorraine mine site, located in the Témiscamingue region, Quebec, Canada. It included, as the main expenditure, a cover with capillary barrier effects (CCBE) used to limit oxygen migration. After construction of the cover, instruments were installed on site to monitor the CCBE performance. Modified oxygen consumption tests were also done to measure the oxygen flux through the cover. Results from water content and suction data, measured from 1999 to 2003, show that the capillary barriers effects are effective and that the water retention layer stays near saturation throughout the years. Oxygen fluxes estimated from monthly water content measures are generally below 10 g/m2/year. Results from modified oxygen consumption tests made on the site give almost similar oxygen fluxes. A two dimension numerical model of the Lorraine mine site was also constructed to verify that mathematical models could predict realistically the in situ conditions on such a large scale site. Numerical results obtained for three years show a good concordance between measured and calculated values. The results obtained form these different evaluation methods for the performance of a CCBE concur and confirm the efficiency of this cover in limiting acid mine generation.

Jan 1, 2005

By M. R. Julien, A. Maqsoud, J. Martschuk, B. Bussière

Acid mine drainage (AMD) from mine wastes is one of the most challenging environmental problems currently facing the mining industry. When mining wastes have the potential to produce AMD, the effluents produced have to be managed to meet existing regulations on water quality. The LTA impoundment (property of Barrick Gold Corp.) located near Malartic, Quebec, contains sulphide tailings that have the potential to generate an acidic leachate. The closure option selected by Barrick was to construct a cover with capillary barrier effects (CCBE), in which the moisture- retaining layer is made of non-acid-generating tailings. Since its construction in 1996, the cover has been monitored to evaluate its performance. For that purpose, various parameters have been measured, including the volumetric water content and matric suction in the different layers of the cover. This paper presents some of the main results from the monitoring program that started eight years ago. The results show that the cover is able to maintain a high degree of saturation in its moisture- retaining layer, acting as an oxygen barrier. The actual performance of the CCBE on the flat surface of the 60 ha site is better than expected at the design stage. The only concern with the LTA cover is the effect of slopes that can reduce the performance of the CCBE during dry periods. However, these effects appear only for short periods of time, and are limited to very localized areas, so that they do not significantly affect the overall performance of the CCBE and its ability to limit the production of AMD.

Jan 1, 2006

By Chris Sammon

The Block 75 portion of the City Creek redevelopment project in Salt Lake City required multiple shoring walls surrounding the 6 acre site constructed to depths ranging from sixty-five to ninety feet below original street grade. Shoring for the project was challenging due to site soils consisting of cobbles, sands and gravels, interlayered lakebed silty clay and fine sandy silt with incised stream deposits of silty/clayey sand and gravels combined with a high groundwater table. Moreover, several abutting structures each with a unique foundation system would be directly or indirectly supported by the shoring system. Three sections of interest are the shoring walls constructed at Main Street, Deseret Trust Building and Eagle Gate Tower. Main Street shoring extended to as much as sixty-five feet below street grade and utilized existing basement walls anchored in place in the upper zones with soil nail walls with pre-installed vertical elements for face stabilization below. Data are presented which illustrates the effect dewatering had on the settlement of the Main Street Shoring. The Deseret Trust Tower shoring supported a 12 story, historical masonry building. Site conditions dictated a separate design for the east side and the north side of the building allowing comparison of relative performance between these walls. Settlements of this structure were controlled by installing micropiles through the 90 year old structures spread footings. Shoring for the Eagle Gate Tower was to be constructed immediately adjacent to a mat supported 22 story high rise structure. This shoring system combined secant piles, ground anchors and incorporated existing abandoned-in-place pipe piles with infilling high pressure jet grouting to create a cutoff wall and eliminate the adverse impacts of dewatering below this sensitive foundation.

Jan 1, 2010

Vertical flow systems (SAPS, vertical flow wetlands) are increasingly used for passive treatment of mine drainage that is net acid. Data on 30 systems in eastern US show that well designed systems typically add about 40 g/d/m2 of alkalinity to influent net acid water. If they are designed with a conservative loading rate of 25 g/d/m2 and carefully constructed, they produce net alkaline water. Alkalinity added depends on influent acidity, Fe, pH, and retention time, and ranges widely, from 7 to 484 mg/L, so this is not a useful design criterion. Some waters may benefit from retention times longer than the conventional 12 - 16 hours, but the design must be partly based on cost-benefit considerations. Systems with fine limestone added to the compost layer perform better than average, perhaps to an alkalinity generation rate of 80 g/m2/d. A variety of problems are noted in the 30 systems and others reported in the literature. Systems with high influent Fe (> ~75 mg/L, varying with pH) tend to gradually decrease in flow rate because of precipitation and settling of Fe hydroxides on top of the compost layer. Some high-Fe systems precipitate Fe in the limestone layer, suggesting inadequate compost thickness, or short-circuiting through thin spots. Systems with Al exceeding about 10 mg/L tend to plug because of Al hydroxide precipitation in the limestone layer. Flushing only removes a small part of this precipitate, but can extend life. Some systems are ineffective because of failure of the inflow system. Some systems are uneconomic because they are oversized. A continuing program of inspection and maintenance is necessary for long-term performance.

Jan 1, 2003

By V Gupta, Z Huang, S K. Biswal

G-Cell is a new design modification of the Imhoflot pneumatic flotation technology, which utilises a self-inducing aerator inside a downcomer, where bubble-particle attachment takes place. The present study has investigated the suitability of the G-Cell technology for cleaning fine coal using a 0.8 m diameter prototype unit at a coal preparation plant operating in the Midwestern United States. A slip-stream obtained from the overflow of raw coal cyclones operating in the plant, containing nominally minus 150 micron size particles and having ash content in the range of 40 per cent to 50 per cent and sulfur content in the range of 1.30 per cent to 1.50 per cent, has been used as the feed for the G-Cell. The performance data produced from the G-Cell tests are found to be very close to the ideal performance curves produced from release analysis. A statistically designed experimental program has been conducted to investigate the parametric effects on various key process responses, such as combustible recovery, product ash and sulfur rejection. The empirical models developed in this study have been utilised to identify a suitable experimental region for achieving a desired combination of response targets.

Jan 1, 2005

By A. Sokolov, M. Demsky, E. Hasikova, V. Gostilo

"Previously, we upgraded and implemented two gamma activation assay (GAA) systems designed to analyse the gold content in raw ores at Zarafshan laboratory, Uzbekistan, and achieved a detection limit of less than 0.05 g/t under actual industrial conditions. Having started to design a fully modern, industrial GAA system for mining companies, this paper analyses the advantages, disadvantages, and special features of all major system components that can influence the sensitivity and accuracy of the analysis. The results of a study to optimize the detector geometry and sample size are presented and the performances of the linear electron accelerator, detector array, and sample transportation system of a modern, industrial GAA system for analysing gold, silver, and rare earth elements are considered. IntroductionGamma activation analysis (GAA) has considerable potential as a future replacement for traditional fire assay analysis in gold mining (Hoffman, Clark, and Yeager, 1998; Morse, 1977; Bourmistenko, 1986, 1981; Sammut, 2016; Tickner et al., 2017). The essence of GAA is to irradiate ore samples with high-energy gamma quanta generated by an electron linear accelerator (LINAC) and then to use a gamma spectrometer to detect the induced activity of the excited gold nuclei. The advantages of this method are discussed in detail elsewhere (Hoffman, Clark, and Yeager, 1998; Morse, 1977; Bourmistenko, 1986, 1981; Sammut, 2016; Tickner et al., 2017), where it is shown that GAA is uniquely suited to analysing ore samples when mining for gold, other precious metals, and accompanying elements.These advantages were realized in three industrial GAA laboratories that were commissioned in Zarafshan, Uzbekistan in 1977, in Magadan, Russia in 1979, and in Batagay, Russia in 1986 (Bourmistenko, 1986; Nii Tekhnicheskoy Fiziki I Avtomatiki, n.d). In 1989, a fourth industrial GAA laboratory was commissioned at a gold mine in Tommot, Russia. However, the project was subsequently halted due to economic reasons (Moshkov and Tjamisov, 2017). Currently, only the laboratory of the Muruntau mine in Zarafshan, Uzbekistan is in operation. The gamma activation method for gold determination is widely applicable at this mine owing to its high productivity and low cost of analysis. An outstanding aspect is the performance of more than one million analyses per year."

May 1, 2019

By G. V. Theja, V. B. Maji

Large infrastructure projects like tunnel excavations, underground constructions face innumerable risks. For successful completion of these projects, it is essential that we foresee and understand risks that could occur during different phases of the project. One of the risks affecting underground excavation projects is the inaccurate performance prediction of TBMs. As this could severely affect the project, resulting in lower advance rates and could also result in changing the excavation machine or method, due to difficulties in excavation, thereby increasing the overall cost of tunnelling. This makes performance prediction of the TBMs as one of the crucial aspects in tunnelling, as a precise estimation of its performance is required for planning and estimation of time and cost of the tunnelling projects. This performance prediction of TBM is a challenging geotechnical problem that is intricate and complex in nature, this is possibly due to the fact that TBM performance prediction involves understanding the rock fragmentation process in wide range from micro-scale (i.e. the interaction of surface of rock material and cutter tip) to macro-scale (including the interaction of rock mass and TBM). Thus in order for the performance prediction model to be efficient, parameters of both TBM specifications and ground conditions have to be considered. Various models have been proposed by researchers since the early phases of TBM application, these studies resulted in the development and improvement of numerous penetration prediction models. Most of these models consider the geotechnical parameters that are input to the model to be consistent along the TBM drive and neglect the uncertainties in parameters that occur. And so to improve the predictive capability of these models and to incorporate the above uncertainties, the penetration rate is modeled as a stochastic variable depending on the geotechnical and TBM parameters, its statistical distribution is determined and is used to characterize the penetration rate instead.

Jan 1, 2015

By Nobuharu Isago, Atsushi Kusaka, Kosuke Kawata, Dohta Awaji

"The immediate ring closure method, in which the entire periphery of the excavation area is closed immediately with an initial support within a short distance from the excavation face, has been increasingly used in Japan, especially, as one of the most effective countermeasures against difficult ground conditions in conventional tunneling. For reasonable design of this method, the performance requirements for the initial support should be clearly stated. The analysis of construction data of 30 road tunnels and the three-dimensional numerical modeling based on real data suggest that the immediate ring closure stabilizes the tunnel structure and the ground around it because of the inner pressure effect of the initial support, especially, for low ground competence factor and small internal friction angle. Finally, the bending compressive strength and the cross-sectional geometry of the initial support have to be considered in the tunnel design while considering the earth pressure and ground properties. INTRODUCTION Conventional tunneling methods often deal with difficult ground conditions such as soft ground or squeezing ground conditions. The immediate ring closure method, in which the entire periphery of the excavation area is immediately supported within a short distance from the excavation face (Figure 1), has been increasingly used in Japan as one of the most effective countermeasures against difficult ground conditions in conventional tunneling (e.g. Takahashi et al., 2011; Nakaoka et al., 2013). The immediate ring closure method was empirically identified as effective for reducing ground surface subsidence and tunnel deformation. However, the working effects of the method have not been clarified sufficiently. To improve the design of this method, the working effects of this method and the performance requirements for the initial support need to be clarified. The relation between the effect of immediate ring closure and earth cover has been clarified (Mashimo et al., 2008; Awaji et al., 2013),"

Jan 1, 2016

By Vijaya Bhushan Rao, Jason Redgers

The typical Vibrocompaction projects undertaken in the UAE are on reclaimed Sands. These Sands which are predominantly the crushable, calcareous, carbonate sands found locally as opposed to the more common quartz or silica sands that are featured in most design literature. The famous reclamations such as the iconic Palm Jumeirah in Dubai, often have specification for mitigation of liquefaction induced settlements, bearing capacity increases and total and differential settlement requirements. Often these performance targets are achieved by the means of achieving a particular relative density that are generally measured by a defined Cone Penetration Test, CPT targeting values of cone resistance (Qc), MPa at respective depth zones. In this paper some case studies are presented, where soil suitability for deep compaction by vibratory methods was firstly assessed for suitability using the Massarsch, 1991 compactability chart prior to the application of vibrocompaction and its subsequent evaluation. One such project named the Island Development required 17 to 23m depth of penetration only to treat the lower 5 to 6m of sand above rockhead as eventually the top 15m of sand will be further excavated to allow for the construction of basement. The paper will present pre and post CPT results, the results of initial site calibration trials and evaluation of the completed works.

Oct 1, 2022

By Tim Wolf, Barry Fink

Mine site managers reported occurrences of locking assembly bolt failures on the Enlow Fork Coal Mine's slope belt conveyor. The observations were made after a number of years of operation and raised questions as to the status of the assemblies in operation. These questions prompted a detailed review of the situation by independent consultants. Using operational history of the conveyor and confirmation of belt loads by static and dynamic methods, a locking assembly fatigue curve was created to suggest expected service life. From this work, suggestions were made to modify the pulley assemblies for extended service life.

Jan 1, 2002

By L M. Stodart

In the increasingly competitive environment of the 1990's, there is a need to provide the users of explosives with accurate and immediate information. Research has shown that information technology alone will not provide companies with a sustainable competitive advantage. However, where information technology is used to assist the development and enhance the performance, of the employee sustainable competitive advantage can occur. A Performance Support System is a tool that combines explosive's theory, government regulations, and site specific knowledge in an easily accessible computer program. In this paper five areas are addressed where a Performance Support System can assist the user: as a reference source, in an assistant or advisory role, as a instruction aid, in regulatory compliance, and as an operations monitor.

Jan 1, 1993

By R. G. Stickney

INTRODUCTION The Basalt Waste Isolation Project, conducted by Rockwell Hanford Operations under contract to the U.S. Department of Energy, is assessing the feasibility of the disposal of commercial radioactive spent fuel/high-level waste in deep geologic formations in basalts beneath and within the Hanford Site in southeastern Washington State. The Basalt Waste Isolation Project mission is to identify and characterize a potential geologic repository site in basalt and to develop associated facilities and technology required for the potential permanent isolation of radioactive wastes in basalt formations. In support of the Basalt Waste Isolation Project, a laboratory testing program was conducted to evaluate the performance of the Council for Scientific and Industrial Research's "Doorstopper" biaxial strain cell. To support site characterization studies and the design of repository openings, in situ stress measurements will be conducted within the reference repository horizon (~970 m). The Doorstopper is one of the instruments being considered for use in these measurements. It was selected because it requires only a small volume of work to achieve stress relief, which is important in a closely jointed basalt. Also, test durations are short, permitting a large number of measurements to be made within a given time to increase confidence in the results. Within the reference repository horizon, temperatures are expected in the range of 40º to 60°C with a humidity of up to 100%. For this testing program, test conditions were selected to closely resemble those expected within the repository horizon. The Doorstopper test, mainly developed by Leeman (1964), is a strain rosette relief method of measuring rock stress in situ. The Doorstopper consists of a four element, 45º strain gage rosette

Jan 1, 1984

By Haijian Fan

Currently, deep foundation designs for the service limit state are deterministic in nature. The settlements and lateral deflections of deep foundations are calculated by means of numerical techniques whereby the foundation-soil interactions are characterized by discrete load transfer curves such as t-z or p-y curves. The noted deficiency of the deterministic approach is that the uncertainties arising from various sources, such as soil properties and model errors are not considered. To address this deficiency, a performance-based reliability design methodology is developed using Monte Carlo statistical methods. The performance based design criteria are defined in terms of the specified allowable displacement. The input to the numerical solution techniques, including the soil strength parameters, unit weight of the soil are relevant to the generation of the load transfer curves are treated as random field. The well established random field generator algorithm, local averaging subdivision, is used to generate random samples of input, where the mean values, variances, the probability distribution, and correlation structures are required statistical parameters for these random variables. The objective of the performance based reliability design is to determine the optimized foundation dimensions so that the probability of failure is less than the target probability of failure. The probability of failure by the Monte Carlo approach is simply the ratio of the number of unsatisfactory performance to the sample size. A numerical example for laterally loaded drilled shaft is given to illustrate the application of the methodology. The incorporation of the correlation length is shown to be critical for properly accounting for the site soil spatial variability.

By Haijian Fan

Currently, deep foundation designs for the service limit state are deterministic in nature. The settlements and lateral deflections of deep foundations are calculated by means of numerical techniques whereby the foundation-soil interactions are characterized by discrete load transfer curves such as t-z or p-y curves. The noted deficiency of the deterministic approach is that the uncertainties arising from various sources, such as soil properties and model errors are not considered. To address this deficiency, a performance-based reliability design methodology is developed using Monte Carlo statistical methods. The performance based design criteria are defined in terms of the specified allowable displacement. The input to the numerical solution techniques, including the soil strength parameters, unit weight of the soil are relevant to the generation of the load transfer curves are treated as random field. The well established random field generator algorithm, local averaging subdivision, is used to generate random samples of input, where the mean values, variances, the probability distribution, and correlation structures are required statistical parameters for these random variables. The objective of the performance based reliability design is to determine the optimized foundation dimensions so that the probability of failure is less than the target probability of failure. The probability of failure by the Monte Carlo approach is simply the ratio of the number of unsatisfactory performance to the sample size. A numerical example for laterally loaded drilled shaft is given to illustrate the application of the methodology. The incorporation of the correlation length is shown to be critical for properly accounting for the site soil spatial variability.

Jan 1, 2017

By Glenn Tobin

The overarching goal in modern drill and blasting operations is that of optimising mining operations to achieve higher levels of productivity, safety, profitability and sustainability. Air decking, a technique used in drill & blasting to optimise explosive product use while achieving a target rock fragmentation1, is a technique that when executed correctly is proven to achieve consistent results independent of rock strength and the position of the holes (single, multiple, vertical, slanted), as well as being proven to reduce super-fragmentation (under-size or fines) while able to achieve optimal fragmentation, especially in the stemming zone2. The ‘shock absorber effect’ if the air deck reduces ground vibration and air blast3. Additionally, the practice of loading explosive product directly in saturated ground without dewatering or lining prior is an increasing global trend.

Jan 1, 2012