Abstract: We conducted a one-dimensional vertical infiltration test on a loess soil column considering the effects of vibration to examine how combinations of vibration frequency and amplitude affect the temporal variation of volumetric water content and the evolution of the wetting front. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were used to reveal microscopic evolution. Using the experimental data, we determine the unsaturated permeability coefficient of loess with three methods—the VG-M model, the wetting-front advancement method, and the instantaneous-profile method—and perform a comparative analysis. The results indicate that vibration accelerates the water infiltration rate. Under vibration, the depth of the wetting front increases with higher vibration frequencies, and the time required to transition from unsaturated to stable infiltration decreases as the vibration frequency increases. All three methods effectively capture the enhancement of the permeability coefficient due to vibration. The results from the instantaneous profile method and the VG-M model are relatively close, while the unsaturated permeability coefficient calculated using the wetting front advancement method is slightly lower. In the initial stage of the loess soil column’s microstructure evolution, medium pores dominate the soil's internal structure. During the intermediate stage, under the coupled effects of vibration and seepage, the proportion of large pores increases, forming seepage channels. In the later stage, the soil’s microstructure stabilizes, with a significant reduction in large pores and an increase in small and micro pores.

Key words: loess soil column, vibrational action, infiltration characteristics, microscopic evolution, unsaturated permeability coefficients