Temperature, Moisture, and Deformation Characteristics of Biochar-Stabilized Silty Clay during Freeze–Thaw Cycles

The stability of silty clay is significantly affected by factors such as the initial water content, mineral composition, pore structure, and environmental temperature. In addition, silty clay exhibits intricate freeze–thaw behavior in cold regions. Biochar, which is an environmentally friendly soil amendment, has significant potential for soil improvement owing to its porous structure, high specific surface area, and chemical stability. In this study, silty clay and straw biochar were selected as materials for investigation. Laboratory freeze–thaw (F–T) cycle tests were carried out to assess the influence of varying biochar contents (0%, 1%, 2%, and 3%) on the temperature, unfrozen water content, and deformation of biochar–silty clay mixtures during F–T cycles. The results showed that incorporating biochar reduced the thermal conduction rate in the silty clay and increased the temperature gradient within the soil. The adsorption effect of the biochar decreased the proportion of free water in the biochar–silty clay mixture, thereby reducing its freezing point. Furthermore, the biochar content significantly influenced the volumetric unfrozen water in the biochar–silty clay mixture. As the biochar content increased, the maximum lag in the volumetric unfrozen water in the F–T cycles gradually decreased. Adding biochar effectively mitigated deformation in soil in the F–T cycles, with the most significant suppression of deformation occurring at a biochar content of 2%. This study provides an experimental basis for the moisture, temperature, and deformation behavior of biochar–silty clay mixtures during F–T cycles, offering guidance for soil improvement in cold regions.