Hydraulic Conductivity of Compacted Clay Frozen and Thawed In Situ

Abstract

A large specimen of compacted clay (diameter = 298 mm; thickness = 914 mm) was subjected to freeze‐thaw in the field for 60 days. Afterward, the hydraulic conductivity was measured. The hydraulic conductivity of the entire specimen remained essentially unchanged, but increases in hydraulic conductivity of 1.5–2 orders of magnitude were observed above the freezing plane. The increase in hydraulic conductivity was highest at the top of the specimen and decreased with depth. Changes in hydraulic conductivity also occurred at depths 150 mm below the freezing plane, where desiccation occurred because of water redistribution, Numerous horizontal and vertical cracks formed in the soil mass. Dissection of the sample after permeation revealed that the cracks were laden with water. Cracking was greatest at the surface and became less frequent with depth. For depths greater than 150 mm below the freezing plane, cracking was absent. The frequency of cracks is consistent with principles of mechanistic models of soil freezing. The results of laboratory tests were used to predict the hydraulic conductivity of the large specimen. Tests were conducted on specimens subjected to various freeze‐thaw cycles, temperature gradients, and states of stress. It was found that the predicted hydraulic conductivities were lower than those measured on the large specimen, but they closely resembled the trend in hydraulic conductivity with depth.