UBC Theses and Dissertations

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UBC Theses and Dissertations

On the use and interpretation of the Continuing Erosion Filter (CEF) test Tham, Emily


The Continuing Erosion Filter (CEF) test was developed by Foster and Fell (1999) to evaluate filter compatibility between base-filter soil combinations. There are existing embankment dams that were constructed with filters that were too coarse by design or have segregated during construction and therefore do not satisfy modern design criteria. If a filter is designed in accordance to the base soil that it is protecting, then it should retain and restrict erosion of the base. The current study uses the CEF test to assess filter compatibility by conducting a sensitivity analysis on a range of shell (filter) gradations against core (base) materials from Dam S. The test observations enable an assessment of filter compatibility, and an evaluation of the Foster and Fell (2001) boundary criteria for no-erosion, excessive-erosion and continuing-erosion. Based on the test results, the onset of filter incompatibility in Dam S core material is observed to occur at a value of DF15 slightly larger than the excessive-erosion boundary, and significantly smaller than the continuing-erosion boundary. Interpretation of the results of the current study on Dam S materials is compared with additional data reported for two other dam materials, using the same CEF test device at the University of British Columbia. Eroded mass loss does not yield a unique boundary to filter incompatibility for the three dam materials tested. Although mass loss increases with increasing DF15/DB′85, there is no distinct change in the trend that correlates to the onset of base-filter incompatibility. In contrast, outflow rate provides a clear and unequivocal distinction between tests that sealed and tests that did not seal. Outflow rate correlates very well with the relatively narrow range of 7 < DF15/DB′85 < 8 where base-filter compatibility transitions between a successful test that seals the filter, and an unsuccessful test that does not seal the concentrated leak.

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