Spatiotemporal infiltration characteristics in intact loess: In situ three-dimensional seepage

Water infiltration in loess is one of the most significant processes that can lead to geological disasters on the Loess Plateau in China. However, the spatiotemporal characteristics of infiltration in intact loess, particularly the heterogeneity of three-dimensional (3D) seepage and its relationship with soil properties, remain poorly understood. This study conducted field infiltration tests on a 3 m × 3 m loess column, instrumented with 48 moisture sensors to monitor 3D seepage and infiltration rates. Both horizontal and vertical infiltration behaviors were analyzed, alongside a detailed characterization of soil physical properties. The results demonstrated that the water infiltration process was significantly heterogeneous in intact loess, with wetting front velocities varying considerably across profiles and depths, despite relatively uniform physical properties. The infiltration process also exhibited pronounced anisotropy, with vertical wetting front velocities at least 10 times higher than those of the horizontal velocities. The in situ tests indicated that the physical properties were not the primary factors influencing infiltration. However, the microfeatures that facilitated the formation of preferential pathways exerted the most significant influence on the water infiltration process in thick unsaturated loess. Additionally, prior infiltration events negatively impacted subsequent infiltration in thick unsaturated loess. These findings enhance the understanding of loess infiltration dynamics, providing insights into unsaturated flow processes and their implications for geological stability in loess regions.