Operations and Monitoring
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In 2007, CDA published a set of technical bulletins to supplement Dam Safety Guidelines. The technical bulletins suggest methodologies and procedures for use by qualified professionals as they carry out dam analyses and safety assessments.
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The use of cemented paste backfill (CPB) is becoming increasingly more common at underground mines worldwide. Part of any CPB design includes the specification of the (typically) shotcrete barricades that retain the CPB within the stope during filling. Newmonts Tanami Operations (NTO) has started an in situ barricade stress monitoring program. The data from this program will provide a basis for comparison of several models that can be used to model the capacity of these barricades. These models vary in complexity from analytical solutions to 3D numerical models. Part of the comparison will include a discussion detailing the required material inputs and how these inputs were obtained. Analysis of this comparison will provide additional understanding on what parameters affect the ultimate capacity of a shotcrete barricade.
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Tailings are finely ground waste rock produced as a by-product of standard mining projects as well as some industrial and power plant operations. Tailings are conventionally impounded behind a dam that is raised perpetually insofar as operations continue, thus amassing large volumes of materials (sometimes including supernatant pond water) in the process. The failures of some tailings impoundments have triggered downstream mass movements that have caused human, economic and environmental impacts, thus inviting considerable public attention and scrutiny. Developing a detailed inventory of these tailings flows facilitates a better understanding of the magnitude-frequency statistics, preconditioning and trigger variables, breach-outflow processes and downstream runout behaviour. Upon screening over 350 historical waste impoundment failure incidents in pre-existing secondary datasets, we have developed a comprehensive global database of 63 tailings flows from 1928-2020 while following strict case selection criteria with the support of satellite imagery, digital elevation models (DEMs) and source literature. Using a novel runout zonation method, the satellite images and DEMs were analyzed on geographic information systems (GIS) platforms to independently estimate runout distances, inundation areas and travel path angles of tailings flows. Depending on data availability or quality, we also summarized the background information, impoundment conditions and geotechnical indices to provide site-specific context to case histories. The collated data is aimed to (i) broaden the scholarly understanding of tailings breach-runout behaviour, (ii) provide comprehensive documentation while assessing the limitations of data availability and/or quality in the public domain and (iii) establish a consistent framework for reporting various properties of tailings dam failures and tailings flows. Lastly, we note that the data should be treated with prudence. Tailings impoundments are highly variable depending on the locality, and site-specific conditions exert strong controls on post-breach behaviour. As such, it is recommended that our database be used purely as a basis for screening-level assessments, case analog comparisons and academic research. For site-specific prediction studies undertaken by practitioners, targeted field observations, laboratory investigations and numerical models are essential.
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Estimation of fines and solids content in tailings oil sands deposits is imperative for tailings planning as well as reporting tailings inventory to the regulator. This report reviews the development of a proper procedure for the engineering assessment of uncertainty in reported tailings mass/ volume as a function of data spacing.
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Quote from main page: A Guide to the Management of Tailings Facilities (the Tailings Guide) is designed to be applied by MAC members and non-MAC members alike, anywhere in the world. The Tailings Guide, first released in 1998, provides guidance on responsible tailings management, helps companies develop and implement site-specific tailings management systems, and improves consistency of application of engineering and management principles to tailings management.
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Tailings storage facility (TSF) design has long been based on deterministic limits. By extension, the TSF owner accepts a Probability of Failure (PF) associated with these deterministic limits which are assessed against industry norms with respect to investigation/analysis and design assumptions related to the operation of the facility. If the Probability of Failure of a design that is derived in this way is taken as the likelihood related to the tolerable risk limit, it follows that the same, or a lower PF, should be maintained during operations. Examples of operational controls include pond management and inspections/monitoring. Upset conditions arise when operational controls are not being implemented. Therefore, by comparing the calculated PF of the TSF complying with the design assumptions and the PF for the same TSF in an upset condition, the required PF of operational controls can be estimated. This concept assists the TSF owner in determining what is required to safely operate the facility and communicate the geotechnical risk to all stakeholders. By extension, scenarios where a TSF owner cannot achieve the required PF of operational controls can be addressed with: 1. Greater rigor applied to operational controls. 2. Addition of more operational controls. 3. A change to the design assumptions, where the timing of the project allows. This method provides a measured approach to risk management in the design and operational phases, without a TSF owner having to quantify an acceptable risk tolerance. Instead, the design is based upon widely accepted practice and industry/business accepted safety, economic and environmental risk levels. Subsequently, the design PF can be calculated and then applied as a benchmark for operations. This approach serves to reduce uncertainty through alignment of the design and operation phases. The concept is explored for three different tailings storage methods: upstream raised TSF, downstream raised TSF, and impoundment by mine waste dumps, to estimate how sensitive each storage method is to the type and effectiveness of operational controls implemented by the dam owner.
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Many publications are available that provide statements of best practice in terms of open pit slope risk management. However, to date none provide a risk model that demonstrates the risk reduction achieved for applying each of the risk management elements. This leaves the slope stability practitioner unable to analytically answer questions such as: ? How frequently should slopes be inspected? ? How frequently should prisms be read? ? Should a radar be acquired? If so, which one? ? How many monitoring systems to use? And many more. This paper applies the Venter and Hamman (2018a) temporal safety risk model to an open pit in West Africa. The paper demonstrates the use of the model to a small saprolite open pit and concludes with recommendations for slope instability registers to facilitate future back?analysis in terms of this model.
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One of the most critical issues when designing a slurry system is sedimentation of solid particles in pipelines and pumps. In pipelines, sedimentation will occur when the transportation velocity of a slurry through the pipe is below the deposition velocity. As soon as particles are settled, there is a considerable risk that, in time, a plug will be created which will block the pipeline completely. Settling of solids can, however, also be detrimental for piston diaphragm pumps; large and heavy solids may settle within the diaphragm housing, on top of the suction valves. This layer of solids will cause diaphragms to rupture. In addition, there is a risk that the settling particles may block the valve, causing pressure surges and further damage to the downstream equipment. In order to determine the settling behaviour of a slurry, costly and time-consuming loop tests need to be executed in specialised laboratories for which large quantities of solids are required. This test may also be an indication of the settling behaviour of solids within a piston diaphragm pump, but would not be very accurate, leaving risk of damage to diaphragms. Therefore, a simple, quick and inexpensive test (SE: sedimentation detection system with evaluation algorithm) was developed which indicates if a slurry is prone to settling or not, by determining how fast solids will settle within a diaphragm housing. For this test, just a few kilograms of solids are required, and the result of the test is known within a very short period of time. In principle, the test is based on the measurement of the speed at which particles settle on a scale; the faster the particles settle, the higher the risk of a settled pipeline and the higher the transportation velocity needs to be. This paper will describe the methodology of this test, its results and interpretation. Also, a technology will be presented which prevents settling of solids within the diaphragm housing of piston diaphragm pumps.
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Planning, operating, monitoring and closing a tailings storage facility (TSF) can present many challenges, especially in dynamic mining environments where site conditions vary spatially and with time. However, big impacts can be made at relatively small cost once the tailings management system, design and performance are well defined and understood. This paper presents various examples of initiatives aimed at achieving the design intent that have been adopted by Rio Tinto Iron Ore, which also reduce risks and improve tailings management performance. Examples presented include development and communication of short-term, long-term and life-of-facility deposition plans, implementation of simple deposition management tools, monitoring and managing slurry density, development and continual oversight of water balance models, and sound investment in water management infrastructure extending to safe performance in emergency situations. Regular governance was also implemented to provide assurance that these controls remain effective.
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Geoprofessional Business Associations (GBA) Tailings Engineer-of-Record (EOR) Task Force published a Business Brief to inform and educate Member-Firms of the ever-increasing levels of risk associated with tailings dams.
