The effect of freeze-thaw cycles on the hydraulic conductivity and structure of a 10% sand-bentonite mixture

Sand-bentonite barriers have often been used for landfill covers and liners at waste containment facilities where clay is not readily accessible. Freeze-thaw effects have been well documented for compacted clay barriers which generally show an increase of hydraulic conductivity from one to three orders of magnitude. However, previous research indicates that sand-bentonite barriers are not affected by three dimensional freeze-thaw cycles. In this paper, a sand-bentonite mixture of 10% bentonite content was subjected to one and three dimensional freezing and thawing in the laboratory. One dimensional freezing simulates in-situ conditions and yields different freezing patterns than three dimensional freezing. Once the specimens reached specified cycles (1, 5, 10, and 15) of freeze-thaw, the hydraulic conductivity was determined. Hydraulic conductivity tests on specimens with an initial value of 4.8 x 10-9 cm/s changed to a value of 4.0 x 10-9 cm/s after fifteen one dimensional freeze-thaw cycles and 3.4 x 10-9 cm/s after ten three dimensional freeze-thaw cycles (i.e., virtually no change in hydraulic conductivity) proving that one dimensional and three dimensional freezing and thawing produce similar results. In addition, frozen thin sections and x-rays were prepared of specimens to evaluate the effects of freeze-thaw on the structure of the soil. A hydraulic conductivity unaffected by freeze-thaw is important in areas where sub-zero degree Celsius temperatures are encountered