Granular Filter Design and Performance Considerations for Aging Embankment Dams

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  • Embankment dams have been constructed in Canada and the United States for over one hundred years. Embankment dams are owned by government bodies, mining and resource companies, hydroelectric producers, and other entities. Dams that have been in service for many years may have a high hazard rating due to the consequences of potential failure, as development tends to expand towards these structures over time. Older embankment dams precede the development of modern filter design criteria, which were first developed in the 1920s and have undergone considerable progress and refinement since. The lack of appropriate filter design in aging dams may increase risk of internal erosion and eventual failure. Risk assessment procedures and monitoring programs are the primary tools used by dam owners and operators to evaluate the risk of and detect potential failure events.
    A brief summary of modern filter design has been presented. Traditional particle-sized based criteria were reviewed and recent developments in constriction-based criteria were discussed. Considerations for challenging base soils, such as dispersive and broadly graded soils, were provided.
    The effects of aging on dam filter properties and performance were discussed. Evidence of filter degradation over time exists in the literature and has been attributed to several causes. These factors include filter clogging, changes in water quality, mechanical degradation, and the development of internal instability and each has been examined.
    A discussion of risk assessment and monitoring for aging dams has been provided. Three of the most widely-used methods were summarized. Most risk assessment methods use a potential failure mode analysis framework. The numerous uncertainties associated with an aging structure presents challenges when attempting to apply potential failure mode analysis. The results of a risk assessment investigation are typically used to identify areas that may require additional investigation, potential remediation actions, or increased monitoring. They are also used as a basis for emergency planning. Monitoring techniques provide information about the location and rate of seepage in and through the embankment. Monitoring is typically the first indication of an internal erosion event that may lead to failure. Improvements in monitoring techniques have decreased detection time and increase likelihood of successful interventions that prevent failure.

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    Attribution-NonCommercial 4.0 International