Due to climatic factors and rapid urbanization, the soil in the Loess Plateau, China, experiences the coupled effects of dry-wet cycles and chemical contamination. Understanding the mechanical behavior and corresponding microstructural evolution of contaminated loess subjected to dry-wet cycles is essential to elucidate the soil degradation mechanism. Therefore, direct shear and consolidation tests were performed to investigate the variations in mechanical properties of compacted loess contaminated with acetic acid, sodium hydroxide, and sodium sulfate during dry-wet cycles. The mechanical response mechanisms were investigated using zeta potential, mineral chemical composition, and scanning electron microscopy (SEM) tests. The results indicate that the mechanical deterioration of sodium hydroxide- contaminated loess during dry-wet cycles decreases with increasing contaminant concentration, which is mainly attributed to the thickening of the electrical double layer (EDL) by Na & thorn; and the precipitation of calcite, as well as the formation of colloidal flocs induced by OH-, thus inhibiting the development of large pores during the dry-wet process. In contrast, the attenuation of mechanical properties of both acetic acid- and sodium sulfate-contaminated loess becomes more severe with increasing contaminant concentration, with the latter being more particularly significant. This is primarily due to the reduction of the EDL thickness and the erosion of cement in the acidic environment, which facilitates the connectivity of pores during dry-wet cycles. Furthermore, the salt expansion generated by the drying process of saline loess further intensifies the structural disturbance. Consequently, the mechanical performance of compacted loess is sensitive to both pollutant type and concentration, exhibiting different response patterns in the dry-wet cycling condition.

Loess has a unique structure that makes it susceptible to liquefaction during intense seismic activity. Liquefaction is closely linked to microstructural changes due to hydraulic coupling. This study examined the threedimensional microstructure evolution of loess in various liquefaction states using dynamic triaxial tests and high-precision micrometer CT scanning. As the ratio of pore water pressure (Rwp) increases, the size of loess particles tends to decrease while the roundness is inclined to increase. Moreover, the morphology and orientation of particles remain relatively stable under such circumstances. In addition, increasing Rwp will decrease the number of macropores, increase the number of mesopores and fine-pores, and decrease the size of throats and channel length, with which petite throats and pores become more prominent. Consequently, liquefaction gradually opens closed pores, enhances soil connectivity, and divides large pores to increase small to mediumsized pores, improving pore distribution uniformity. Liquefaction induces the pore shape coefficient to decrease, the number of slim pores to increase, and irregular and circular pores to decrease. These findings provide a scientific foundation for preventing and evaluating loess liquefaction disasters and shed light on the microscopic mechanisms of loess liquefaction.