Elizabeth Gardiner, Len Murray, David Gladwin
Abstract: The Mining Association of Canada has worked over the past 12 years to improve the management of tailings facilities. This effort began out of a realization that tailings present a major business risk to the mining industry, and that a series of major tailings failures around the world in the 1990’s were fundamentally indicative of need for improved care and management practices by tailings dam and facility owners and operators. MAC established and continues to sponsor the Tailings Working Group, which has assisted in development and publication of a three-volume set of guides to improve tailings management:
•“A Guide to the Management of Tailings Facilities”, initially published in 1998, updated edition published in 2008;
•“Developing an Operation, Maintenance and Surveillance Manual for Tailings and Water Management Facilities”, published in 2003; and
•“A Guide to Audit and Assessment of Tailings Facility Management”, published in 2008.
The three guides provide a strong message that the key to safe and environmentally responsible management of tailings is consistent application of sound engineering capability within an effective management framework.
The documents are almost directly applicable to all forms of dams and are widely used for water dams. Also, because the documents are available in Spanish and French they have found wide use in International projects.
A brief comparison with published ANCOLD guidelines is provided.
Keywords: Management of tailings facilities and water dams, Operation, Maintenance and Surveillance, Auditing, risk, safety, guides
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Jeffrey A. Schaefer
Abstract: The U.S. Army Corps of Engineers (USACE) has numerous dams built on limestone foundations that are susceptible to solutioning (karst). Significant dam safety issues related to the karst foundation have developed in many of these projects. Screening risk assessments of the USACE portfolio of dams has shown that defects related to karst foundations is one of the largest contributors to our risk. To better evaluate this risk, a method to estimate the probability of failure from piping into karst foundations has been developed by team of experts from the University of New South Wales, URS, the US Bureau of Reclamation, the US Army Corps of Engineers. This paper summarizes the major failure modes associated with dams on karst foundations and the methodology developed to perform risk analysis. A summary of USACE case histories with karst foundation issues and recent projects to remediate the foundations are also included.
KEYWORDS: Dam, Seepage, Karst, Solution Feature, Risk
Jerome Argue, Steven Slarke, Douglas Rudd
Abstract: The North Para River Flood Control Dam is an integral part of the works proposed to manage flood risk in the Gawler River, north of Adelaide. Undertaken by the Gawler River Floodplain Management Authority (GRFMA), an authority representing the six local Councils in the area, the flood storage is located on the North Para River, about 10 kms north of Gawler. Roller Compacted Concrete (RCC) was selected for the construction material, based on an assessment of the geotechnical and geological site conditions, together with advantages of reduced cost, time and structure required to pass design flood events. With an overall project cost of $16.1 million, the dam was constructed on time and well within pre-tender budget estimates.
Keywords: flood mitigation, roller compacted concrete, North Para River, construction.
Francisco Lopez, John Bosler
Abstract: A study has been undertaken to determine the structural adequacy of the Intake Tower for the Dartmouth Dam Low Level Outlet Works under the Maximum Design Earthquake (MDE). The tower is a reinforced concrete frame structure. The study included the definition of appropriate seismic inputs and nonlinear time-history analyses for different levels of ground shaking.
The behaviour of the tower was assessed in terms of material strains. The seismic acceleration-time history was applied to the model and the nonlinear analysis identified the locations in the structure which reached the following performance thresholds: cracking of core concrete, yielding of reinforcing steel, fracture of reinforcing steel and crushing of core concrete.
The results of the study showed that the tower was able to resist, without collapse, the loadings imposed by three different MDE acceleration time-histories. The predicted level of damage consisted of generalised yielding of reinforcement, formation of numerous plastic hinges at different locations in the tower and generalised spalling of cover concrete.
Overall, the structural response of the tower under the MDE events was considered satisfactory and met the performance requirement that structural collapse should not occur.
Keywords: intake tower, nonlinear, inelastic, time-history, seismic analysis.
Richard John Kenny
Abstract: Physical hydraulic models have traditionally provided the input to spillway design.
However, the application of Computational Fluid Dynamics (CFD) is increasing in popularity.
The reliability of CFD depends on several complex issues including the physics of the flow regime, the mathematical formulae describing the fluid flow and the solution method. CFD reliability should be confirmed for each particular application, including ogee spillways (common discharge structures on dams).
A literature review has been undertaken to determine validation techniques and the reliability of CFD related to ogee spillways. There is a great deal of information available about the aeronautical, marine, automotive and mining industries but relatively little available about ogee spillways. The degree of validation for ogee spillways was found to vary significantly and raises the question of whether better validation can be achieved. Better validation may improve confidence in CFD techniques.
A project has been undertaken through Queensland University of Technology to model a prototype scale notional 2D ogee spillway using FLUENT CFD software under steady state conditions. The project tests the sensitivity of the CFD results to various parameters. The sensitivity of the inlet mass flow rate was tested for several CFD parameters. The investigation considered:
1.The grid spacing required for geometric convergence;
2.The effect of domain extent on the computational results;
3.The influence of a boundary layer and wall roughness;
4.The importance of the choice of turbulence model; and
5.The impact of inlet turbulence assumptions.
The recommendations of the sensitivity investigations were used for validation against the United States Army Corp of Engineers (USACE) design data.
Excellent agreement was found between the CFD predictions and the USACE values.
Keywords: Computational fluid dynamics (CFD), dam, flood routing, fluent, Navier-Stokes equations, Numerical/computational modelling, Ogee spillway crest, physical model, turbulence.
Dr AK Hughes
Abstract: This paper describes the way in which the UK is moving in respect of reservoir safety and outlines the legislative changes that are currently being drafted. It also identifies issues which the author thinks are important for the future of dam engineers around the world.
Keywords: safety, legislation, risk assessment