Freeze-thaw (F-T) cycle tests and triaxial shear tests are conducted under varying freezing ambient temperatures and different F-T cycles for remolded loess. The results indicate that nearly all stress-strain curves of remolded loess exhibit strain-hardening behavior under varying freezing ambient temperatures and different F-T cycles. A decrease in freezing temperature alters the yield strain of loess and diminishes its resistance to deformation. As the freezing temperature decreases and the number of F-T cycles increases, the failure deviatoric stress of loess initially decreases, then increases, and eventually stabilizes. The most detrimental freezing temperature is -12 degrees C, which significantly exacerbates the adverse effects of F-T cycles on failure deviatoric stress. The strength indices initially decrease and then increase with decreasing freezing temperatures, while they first decrease and then stabilize with an increasing number of F-T cycles. Notably, the deterioration of cohesion is significantly greater than that of the internal friction angle. A quantitative analysis is conducted to examine the relationship between failure deviatoric stress, shear strength index, temperature, and freeze-thaw cycles. The fitting results effectively quantify the influence of different variables on the strength characteristics of loess. The findings of this research have significant theoretical implications for practical engineering applications in the northwest loess region.

The shear strength index of seasonally frozen soil is significantly affected by the freezing-thawing and water replenishment methods. To simulate the actual freeze-thaw and water replenishment process in seasonally frozen soil, a new method called the unidirectional freeze-thaw and natural water replenishment method was proposed. A test device was developed to facilitate this method. By using soil as the medium for water migration, the temperature change and water migration characteristics during the freeze-thaw process were investigated. The study also considered the influence of the samples' water content and the gradient between the water content of the test samples and the water replenishment soil layer. The changes in the soil stress-strain curve, static strength, and shear strength index under freeze-thaw were analyzed based on triaxial tests. The results revealed that the temperature change during the test process can be divided into six stages: rapid cooling, slow cooling, temperature stability, slow heating, continuous phase change around 0 degrees C, and positive temperature stability. After freeze-thaw, the sample water content without gradient increased by approximately 0.6%, while the sample water content with a gradient increased by about 1.5%. However, the distribution characteristics of the water content were different. The static strength, cohesive force, and internal friction angles were all lower after freeze-thaw under different water content conditions. The maximum static strength and cohesion decreased by approximately 50% and 60%, respectively, under freeze-thaw, while the internal friction angle showed a slight decrease. The new freeze-thaw and natural water supplement method can serve as a basis for selecting the shear strength index of seasonally frozen soil.

Expansive soils, characterized by significant volume changes in response to moisture fluctuations, present substantial engineering challenges globally. This study explores the efficacy of lignosulfonate (LS), an industrial by-product, as a sustainable stabilizer for expansive soils. Three soil samples with varying degrees of expansiveness (weak, mid, and strong) were treated with LS, and their geotechnical properties were evaluated. For weak, mid, and strong expansive soil, the optimum lignosulphonate content (OLS) determined based on the free swelling rate and plasticity index was 0.75%, 2%, and 6%, respectively. The addition of LS resulted in a reduction of the liquid limit, plasticity index, and free swell index across all soil types. Furthermore, LS-treated soils exhibited enhanced resistance to volume changes and improved shear strength under cyclic wet-dry conditions. Moreover, crack development is inhibited in LS-modified soil. LS decreases the soil's affinity for water by creating a hydrophobic barrier around soil particles. Furthermore, the interaction between LS and the layered clay minerals results in stronger binding, which contributes to the stabilization process. The findings indicate that LS not only reduces the swelling nature of expansive soils and improves their shear strength and stability under wet and dry cycling conditions, but also provides an environmentally friendly solution for soil stabilization and sustainable construction practices.