Freeze-thaw cycling and the hydraulic conductivity of geosynthetic clay liners concurrent with cation exchange

• Tests were conducted to assess the effect of cation exchange coincident with freeze-thaw cycling on the hydraulic conductivity of a geosynthetic clay liner (GCL). GCLs were prehydrated by contact with silica flour moistened with synthetic subgrade pore water and subsequently permeated with a solution representing the pore water in the cover soil over a tailings facility. Control tests were conducted using the same procedure except deionized water (DI) was used as the permeant liquid to preclude cation exchange from the permeant liquid. The GCLs were subjected to 1, 3, 5, 15, and 20 freeze-thaw cycles, and the hydraulic conductivity and exchange complex were determined after each freeze-thaw increment to assess chemical changes that occurred during freezing, thawing, and permeation. GCLs undergoing freeze thaw cycling experienced little to no cation exchange until 15 freeze-thaw cycles. After 20 freeze-thaw cycles, however, 50% of the sodium (Na) initially in the exchange complex was replaced by calcium (Ca). Dissolution of calciate within the bentonite is a likely source of the Ca. Hydraulic conductivity of GCLs exposed to freeze-thaw cycling was lower than the hydraulic conductivity of a new GCL permeated with DI water (< 2.2x10-11 m/s). A small increases in hydraulic conductivity (~2.3 times), which may have been caused by cation exchange, occured at 15 and 20 freeze-thaw cycles but the hydraulic conductivity remained below that obtained by direct permeation with DI water.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Samhällsbyggnadsteknik -- Geoteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Civil Engineering -- Geotechnical Engineering (hsv//eng)

Nyckelord

Geosynthetic clay liners

cation exchange

hydraulic conductivity

freeze–thaw

clayey till

microstructure

macrostructure

dry cover

Freeze–Thaw

bentonite

montmorillonite

23Na

31P

29Si NMR

interaction

ion exchange

sorption

cover

barrier

tailings disposal

tailings

Geoteknik

Soil Mechanics

Publikations- och innehållstyp

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