Laboratory Testing to Evaluate Changes in Hydraulic Conductivity of Compacted Clays Caused by Freeze-Thaw: State-of-the-Art

Abstract

Several laboratory studies have shown that the hydraulic conductivity of compacted clay may increase up to three orders of magnitude when subjected to freeze-thaw. In this paper, methods to freeze and thaw specimens of compacted clay are reviewed and compared. Methods to measure the hydraulic conductivity of the specimens are also reviewed. Only naturally formed clay soils are considered; soil-bentonite mixtures and other amended soils are not included. A review of testing conditions present during freeze-thaw and their effect on hydraulic conductivity is also included. Testing conditions that are addressed include availability of an external supply of water (closed vs. open system), dimensionality of freezing (one-dimensional vs. three-dimensional), rate of freezing, ultimate temperature, number of freeze-thaw cycles, and state of stress. The rate of freezing, number of freeze-thaw cycles, and state of stress appear to have the largest effect on hydraulic conductivity. The effect of sampling disturbance on the hydraulic conductivity of compacted clay subjected to freeze-thaw is also presented. Specimens removed in Shelby tubes may be disturbed during sampling and extrusion. As a result, the effects of freeze-thaw can be masked. Collecting block specimens of thawed clay or taking core specimens of frozen clay are suggested as alternative procedures. A method to collect block specimens is presented.

Effect of Freeze-Drying on Soil Aggregate Stability

“…The ultimate minimum temperature reached during the subzero portion of the freeze-thaw cycle therefore becomes an important consideration because this, along with the pore geometry, largely controls the proportion of pore water actually freezing. Othman et al ( 1994) found greater increases in the hydraulic conductivity of thawed clays when a minimum freezing temperature of -2°C was used rather than -1°C. Large variation in the data from the -1°C tests also suggested that a large portion of the pore water might have remained unfrozen.…”

Hydraulic conductivity changes of a low-plasticity till subjected to freeze–thaw cycles

“…For instance, in closed-system freezing, drainage is closed and no additional water enters the sample, whereas in open-system freezing, water from an external source is available and, depending on the frost susceptibility of the soil tested, it may be attracted to the freezing front and form significant ice lenses. Othman et al (1993) reported little effect on the hydraulic conductivity changes of thawed clays frozen with or without access to an external water source.…”

A new TDR sensor for accurate freeze–thaw measurement

“…Othman et al (1994) observed significant increase in the hydraulic conductivity of compacted clay (two to three orders of magnitude) within three to five freeze -thaw cycles. Similar phenomena were observed on soft fine-grained soils (Eigenbrod 1996) and in a small-scale field test (Benson and Othman 1993).…”