EFFECT OF FREEZE-THAW ON THE HYDRAULIC CONDUCTIVITY OF THREE COMPACTED CLAYS FROM WISCONSIN

A laboratory testing program that was conducted to evaluate how freeze-thaw affects the hydraulic conductivity of three compacted clays is described. A parametric study was conducted to evaluate how the rate of freezing, temperature of freezing, dimensionality of freezing, and number of freeze-thaw cycles affect changes in hydraulic conductivity. The influence of molding water content, compactive effort, and state of stress has also been evaluated. Although the soils used in this study are of different mineralogical composition and geologic origin, the results show that freeze-thaw has a similar effect on their hydraulic conductivity. In particular, an increase in hydraulic conductivity of one to two orders of magnitude occurs because of freeze-thaw. Physical observations have shown that freeze-thaw causes cracks that act as conduits for flow and hence results in increased hydraulic conductivity. The study has shown that changes in hydraulic conductivity are independent of molding water contents in excess of optimum, but that increases in compactive effort reduce, albeit slightly, the increase in hydraulic conductivity. Results of the study also show that a single freeze-thaw cycle can result in large increases in hydraulic conductivity, but increases in hydraulic conductivity cease after three cycles of freeze-thaw. Conditions during freeze-thaw have also been found to influence the change in hydraulic conductivity. In particular, greater changes in hydraulic conductivity occur at greater rates of freezing and lower freezing temperatures.