ASTM International

Differential Flow Patterns Through Compacted Clays

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The determination of the hydraulic conductivity of compacted clays is vital when the clay is to be used as a liner for contaminant of hazardous waste. Therefore different types of permeameters were used and modified to investigate the homogeneity of a compacted specimens.

Flexible wall and fixed wall permeameters were modified using multiple ring bases to determine the magnitude of differential flow patterns during hydraulic conductivity testing. The hydraulic conductivity was calculated for different portions of the specimen. The outer ring of the specimen was found to have a permeability two to five times larger than that of the core of the specimen, resulting in an overall permeability, which was 50 to 100% higher than that of the core of the specimen. Thorough determination of the variation of the density within a specimen does not explain the variation of the hydraulic conductivity. The clay near the periphery is apparently exposed to a somewhat different type of compaction resulting in a different structure of the clay and thus a higher permeability. Tests with a 19 port base indicated that isolated areas could contain channels where major flow takes place.

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