WINTER EFFECTS ON HYDRAULIC CONDUCTIVITY OF COMPACTED CLAY

A field test was conducted to determine if freeze-thaw cycles cause increases in hydraulic conductivity in the field, as has been observed in laboratory tests. A test pad of compacted clay was instrumented for monitoring temperatures and climatic conditions and partially insulated. The measurements indicated that up to 10 cycles of freeze-thaw occurred in the uninsulated portion of the test pad whereas no freezing occurred in the insulated portion. Hydraulic-conductivity tests were conducted before and after winter to determine if changes in hydraulic conductivity occurred as a result of winter exposure. In situ hydraulic-conductivity tests showed that the overall hydraulic conductivity was similar in the insulated and uninsulated portions of the test pad before and after winter. No change in overall hydraulic conductivity occurred in the uninsulated region because the depth of frost penetration was only 30% of the thickness of the test pad. However, tests on block specimens collected from near-surface soil that underwent freezing and thawing increased in hydraulic conductivity by a factor of 50-300. Similar increases in hydraulic conductivity were measured using laboratory freeze-thaw tests.