Cooperative Research on Field Capabilities Test/Demonstration for Federal Emergency Management Agency (FEMA) Indirect Means of Assessing Conditions within Earth Embankment Dams- Indirect Means of Assessing Conditions (in) Embankment Dams (IMACED) Project.
* What is the most effective means of assessing internal conditions on dams, levees, and dikes using geophysical and other methods, and what is the current state of the practice?
* What is the most effective means of monitoring embankments for changes in seepage and possible internal erosion using geophysical methods identified above?
Need and Benefit
Geophysical test methods have been applied to investigations at dams, levees, and conduits for several decades to aid in delineating uncontrolled seepage and internal erosion. Although some standards and guidelines exist for certain types of geophysical measurements, geophysical testing on embankments is largely based on experience, with more experienced practitioners generally achieving more useful results.
Within the last 5-10 years, the dams community has recognized the value in documenting and standardizing geophysical test methods as applied to embankment seepage and internal erosion investigations. The Canadian Electric Association--Dam Safety Interest Group (CEA--DSIG) geophysics research work is one example of this effort. FEMA Research Needs Workshop "Seepage Through Embankment Dams" vote tallies in Topics one and four list geophysics-related research needs as second- and first-highest, respectively.
A documented field capabilities test/demonstration on an embankment with known deficiencies will serve as a ready case study for engineers, for managers responsible for allocating funds to maintenance, and for other decisionmakers when deciding on possible alternatives to investigate embankment seepage and internal erosion.
Engineers, dam owner/operators, and other dams officials and decision-makers often have expectations for geophysical test results (e.g., resolution, accuracy, uniqueness) that may not reflect the capabilities of the various geophysical methods. Documenting the strengths and weaknesses of the various geophysical methods allows the nonspecialist to make an initial judgment about the applicability of geophysical test methods to certain types of subsurface investigations. The availability of a best-practices guidelines document would improve the effective use of these methods in investigating seepage, internal erosion, and conduit evaluations. The result would be wider and more consistent application of geophysical testing and greater understanding of the test results' implications.
Many government agencies and private dam owners do not have ready access to geophysical expertise and rely exclusively on other agency or contract forces to perform geophysical testing and interpret the testing results. In the absence of best-practices guidelines documents, these geophysical surveys may not achieve their intended objectives, or as mentioned above, expectations for the testing may not be realistic. In its capacity as dam safety lead agency, FEMA recognizes the need for a state of the practice summary and a guidelines document.
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