A Modified Way of Testing Filters for Clay Cores of Embankment Dams


Türker Mirata

Professor of Civil Engineering, Middle East Technical University, 06531 Ankara, Turkey

Tanfer Gürler

Gama Industrial Plants Manufacturing Co., Atatürk Bulvari, 211/7, Kavaklidere, 06680 Ankara, Turkey.


Different forms of testing filters to retain cracked clay cores of dams have previously been proposed. The earliest of these, the perfect filter (PF) test was aimed at designing a filter that would retain the finest particles that would be contained in the eroded material, namely clay flocs. This test has subsequently been found to be too conservative, and an alternative procedure, the no erosion filter (NEF) test, was devised in which a layer of the clay core material is compacted above the filter to be tested, and erosion is induced in a 1 mm to 1.5 mm diameter pinhole in the clay layer by applying a sufficiently high hydraulic gradient.  In the present study, the PF test has been modified to test a representative sample of the actual clay core material by continuously stirring the suspension above the filter to be tested, to prevent the deposition of the coarser material on the filter surface. Three different clay core materials have been tested, and the results found to be in close conformity with those of the NEF test. The modified form of the PF test seems suitable for application as an independent check of the NEF test results.

KEYWORDS: clay cores; embankment dams; filters; laboratory tests; perfect filter test; no erosion filter test.

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