Water-infiltration characteristics of Yunnan red clay under different density conditions

Rainwater infiltration has a significant impact on slope seepage and stability, with the soil compactness exerting strong over infiltration dynamics. To investigate the water ponding infiltration characteristics of red clay soil under different densities, constant-head ponding infiltration test was carried out using an independently designed one-dimensional apparatus on three groups of homogeneous red clay samples from Yongren County, Yunnan Province, with different densities (1.25, 1.35, 1.45 g/cm³). The results show that at the higher dry densities, he response time of sensors increased, the humidification process slowed, and the duration of rapid water content increase was extended by 25.8% and 83.7% respectively with the increase of dry density. The infiltration time curve of the soil column in the three groups showed a parabolic growth, with the vertical migration rate of the wetting front decreasing rapidly from a high initial value to 0.03～0.05 cm/min before stabilizing. By quantifying the morphology of the wetting front column during laterite water infiltration, it is concluded that at the same infiltration depth, the higher the density, the smaller the wetting front horizontal degree index, and the shallower the infiltration depth when the index is stable. The unsaturated permeability coefficient of laterite increases gradually with soil humidification, mainly ranging from 10⁻⁹ cm/s to 10⁻⁴ cm/s. When volumetric water content is below 18%, the permeability coefficient of the three laterite groups has a minor difference; when the volumetric water content is above 18%, permeability is strongly and inversely related to density. When the soil column is humidified to a stable state, the water saturation ranges from 88.2% to 94.9%, and the permeability coefficient of the soil is lower than that of the vacuum saturated sample. This study provides a theoretical basis for the cause analysis and treatment of geological hazards in laterite areas.