Assessing Frost Damage in Compacted Clay Liners

Methods used to assess frost damage (here defined as a large increase in hydraulic conductivity) in compacted clay liners are reviewed and evaluated using data collected from two test pads that were instrumented and then exposed to winter weather. The methods include comparisons of measurements of either water content and dry unit weight or hydraulic conductivity made before and after winter exposure. Field and laboratory methods of assessing hydraulic conductivity are considered. The comparison shows that assessments based on water content and dry unit weight can be misleading. Assessments based on hydraulic conductivity are recommended. Field hydraulic conductivity tests can be useful provided the soil is not disturbed or smeared and the test method permits evaluation of liners partially penetrated by frost. In this study, however, the field tests yielded only qualitative results. Laboratory tests can also be used provided undisturbed specimens of sufficient size are collected. Specimens 70 mm in diameter were of adequate size in this study. Suitable specimens can be collected as blocks from thawed soil or with a core barrel while the soil is frozen. Collecting specimens in thin-wall sampling tubes (i.e., "Shelby" tubes) causes significant disturbance of thawed soil and thus is not recommended. Data are also presented to illustrate that laboratory tests should be conducted at effective stresses similar to those existing in the field.