active layer during rainfall infiltration. Researchers proposed a coupled hydro-mechanical framework for assessing rainfall-induced instability in unsaturated slopes [14; 15]. Their solution can easily be integrated into analyses of natural and man-made slopes and earthen structures subject to infiltration at a regional scale. [PERSON] et al., [PERSON] et al. and [PERSON] evaluated soil water redistribution and hysteresis via experiments [16; 17; 18; 19]. Studies have shown that due to highly nonlinear soil-water characteristics and soil permeability, the infiltration boundary is complex, the initial conditions vary, and the transient process of infiltration is complicated; in addition, the hysteresis of soil-water interactions further adds to the complexity of conducting experiments on the response of soil during the infiltration process [20; 21]. Their tests showed that moisture migration plays an important controlling role in the shear strength of soil, thus affecting slope stability. In the warm season, the active layer slowly melts, the water starts to infiltrate into the slope or soil, the soil moisture content slowly increases and approaches a saturation state, the matric suction gradually decreases to zero, especially for matric suction near the surface, and the pore pressure decreases. This significant change could lead to a decrease in bond strength between the soil particles and a change in structure, thus reducing the shear strength and generating landslides.  
There are many factors involved in slope stability, such as melt, rainfall duration and intensity, spatial and temporal changes of vegetation, saturation, slope, infiltration rate, soil moisture content, groundwater level, and the soil-water characteristic curve (SWCC) [16; 17; 22]. However, these parameters have strong spatial variability. Due to the high cost of field infiltration tests, the complexity of the process, and the complex correlation between rainfall and runoff, these parameters are usually difficult to accurately obtain directly from field infiltration experiments, and they often rely on the establishment of a fuzzy association relationship between rainfall and runoff. Therefore, the soil column vertical infiltration test is an important method for reproducing the rainfall infiltration process on a slope surface. The rainfall infiltration process and mechanism are affected by the initial moisture content, soil water retention, porosity, and evaporation rate [16]. To understand soil infiltration behavior under different rainfall intensities and durations, the initial state, infiltration rate, matric suction and moisture content of soil are extremely important variables when studying the infiltration responses of unsaturated soil slopes [22; 23].  
Vertical infiltration tests were conducted indoors on three silt columns. Rainfall simulations were performed on soils with different densities and surface hydraulic heads. Real-time continuous measurements of wetting front displacement, volumetric moisture content, infiltration rate, and infiltration were performed, and the impact of rainfall on the infiltration process was assessed by analyzing moisture profiles, total hydraulic head profiles, the SWCC, and the hydraulic conductivity function (HCF).