Investigating cracking behavior of saline clayey soil under cyclic freezing-thawing effects

Abstract

This study investigates the cyclic freeze-thaw (F-T) effect on crack patterns in saline clayey soil. Samples with different NaCl concentrations (0 M, 1 M, 2 M, and 3 M) are prepared and subjected to cyclic F-T processes. Each cycle involves freezing the samples at a constant temperature of −20 °C for 24 h and thawing at room temperature (21 °C) for 24 h. Additionally, a parallel experiment is conducted to observe the effects of desiccation at room temperature. The weight and surface crack patterns of the samples are continuously monitored. The image processing technique quantifies crack morphology and determines crack area, surface crack ratio, crack width, crack length, and fractal dimension. The results reveal that as the salt concentration increases, the F-T and desiccation samples exhibit decreased crack area and width. This decrease is attributed to the reduced saturation vapor pressure caused by higher salt concentrations, which slows down water evaporation and delays crack formation. The final crack pattern in the F-T samples is closely linked to the initial pattern of ice crystal formation. Lower salt concentrations result in the formation of larger ice crystals, leading to larger cracks during thawing. In the experiment, where the temperature was above the NaCl eutectic point, only ice crystals were formed, and the salt remained isolated as the salt concentration increased in the unfrozen solution. Conversely, during the freezing process, samples with higher salt concentrations with higher unfrozen solution content experience upward movement of the solution due to temperature gradients and water evaporation. This study provides new insights into understanding the soil water and salt movement and the phenomenon of surface clay soil cracking during the freezing-thawing process.