The structural integrity of slopes in the Ili Valley is critically influenced by the inherent characteristics of loess, particularly when it is subjected to the seasonal climatic changes. In the present research, a series of triaxial shear tests were carried out to examine the mechanical behavior of the Ili loess under different dry-wet and frost-thaw cycles. In parallel, some testing methods, including scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR), were applied to investigate the progressive damage characteristics and the alterations in terms of the microstructures. Test results demonstrated a strong correlation between the macroscopic mechanical resistance and microstructural changes of the Ili loess subjected to the dry-wet and freeze-thaw cycles. The impact of the freeze-thaw cycles was more pronounced than other parameters, when the reduction in shear strength of the Ili loess under dry-wet cycles was accounted for. The results also showed that either the cohesion or the internal friction angle is very different from each other. Furthermore, changes in terms of the microstructure, such as the particle size, porosity, morphology, soil structure, and particle contact mode, exhibited distinct characteristics under varying climates. The research outcomes obtained from this research offer valuable data reference and theoretical guidelines to prevent or postpone the occurrence of the landslide in the Ili Valley under critical environmental conditions.

Soluble salts significantly influence the freezing characteristic parameters of frozen soil. Previous studies have either insufficiently addressed the effect of sodium sulfate on matric suction or not comprehensively revealed the mechanism by which temperature affects matric suction at freezing temperature. In this study, the moisture and suction sensors were used to quantify the freezing temperature (FT), unfrozen water content (UWC), and matric suction (MS) of Ili loess with varying soluble salt contents. The impact of soluble salt content on three freezing characteristic parameters were investigated with the underlying mechanisms revealed. The results indicated that there was an initial decrease in both freezing and supercooling temperatures as the soluble salt content increased. Beyond a soluble salt content of 14 g/kg, an increase in both the freezing and supercooling temperatures was observed. Specimens with different soluble salt contents exhibited distinct UWC, which could be categorized into three stages based on temperature. A crystal precipitation stage was observed beyond the soluble salt content of 14 g/kg. Moreover, the proposed fitting model for UWC by incorporating the soluble salt content into the Gardner model demonstrated high accuracy. The MS can also be divided into three stages with temperature. Notably, specimens with soluble salt contents of 20 and 26 g/kg exhibited nonlinear increases in MS at temperatures of 5 degrees C and 10 degrees C due to crystal precipitation. Furthermore, theoretical calculations indicated the complete precipitation of sodium sulfate during the positive temperature stage.