Effect of Freeze–Thaw Cycles on the Water Absorption and Retention Capacity of Unsaturated Expansive Soil Liners

Understanding the behavior of expansive soil liners is essential to address concerns about retention capacity and unsaturated flow of water through them in geotechnical and geoenvironmental applications. Soil water retention curve (SWRC) is a key parameter associated with unsaturated soil mechanics in such contexts. This study investigates the effect of successive freeze–thaw (FT) cycles on the SWRC of sand-expansive soil liners with expansive soil contents of 20%, 30%, and 60%. The SWRCs of the considered liners before and after exposure to successive FT cycles were measured in the laboratory over the entire suction range, extending to the residual state, using a combination of different suction measurement techniques. Subsequently, an appropriate fitting model was applied over the practical suction range (0–1,000 MPa). The results revealed that exposure to FT cycles decreased the absorption rate of the liners and induced significant changes in their SWRCs by reducing their retention capacity. This effect was observed to be dependent on suction, becoming more pronounced in the capillary and transition zones. In addition, the effect of the FT action was observed to be proportional to the proportion of fine materials or expansive soil content; it also altered the shape of the SWRC. We believe that the results of this study will be of great significance to practitioners in the advanced interpretation, modeling, and prediction of unsaturated soil behavior of liner layers.