To better understand and analyze the unsaturated stability of loess filling body, it is necessary to study the changes in suction stress before and after the drying-wetting cycles. In this study, the SWCC of compacted loess before and after drying-wetting cycles was tested using the filter paper method. Then, the suction stress was calculated and the microstructure of the loess sample was determined by the SEM and NMR. The results showed that the drying-wetting cycles had an important influence on the SSCC and microstructure of compacted loess. The change in suction stress before and after the drying-wetting cycles can be well explained by the loess microstructure. The drying-wetting cycles did not significantly change the basic trend of the compacted loess’s SSCC, but it increased the porosity and the dominant pore diameter of loess, and reduced the suction stress under the same matric suction. The main significant change in suction stress with matric suction occurred within the range of the dominant soil pores. The larger the dominant pore diameter, the smaller the suction stress under the same matric suction. In addition, this study proposes a new method for calculating suction stress based on the PSD parameters.

The study of water infiltration helps to investigate the pollutants' migration, grasp the mechanism of the water cycle, and correctly evaluate water resources. This paper reveals the mechanism of compacted loess's one-dimensional vertical water infiltration characteristics using a low-cost water infiltration device. In addition, it investigates particle arrangement and pore size distribution characteristics using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The test finding suggests that the loess's early-stage infiltration rate is significant, and the dry density is not related to the infiltration characteristics. With the advance of the wetting front, the infiltration rate decreases under air resistance. The unsaturated permeability decreases with dry density at lower matric suction while unaffected by the dry density at higher matric suction. Moreover, the volume and connectivity of pores mainly control the water infiltration characteristics. Finally, based on the test results, a method for rapidly predicting the unsaturated permeability of loess is proposed. The results of the study help predict contaminant transport and guide groundwater extraction and management.