Micro-Mechanism and Permeability of Wetting of Unsaturated Loesses

In this study, the wetting mechanism of loess microstructures is deeply investigated from the perspective of unsaturated soil theory. The research methodology includes the prediction of the permeability coefficient of unsaturated soils using Van Genuchten model and Fredlund model, and variable head permeability test. The experimental results showed that the increase of percussive water content led to a significant decrease in the saturated permeability coefficient of the soil samples, which decreased by nearly 100 times when the percussive energy was elevated from 590.3 kJ/m3 to 2705.6 kJ/m3. With the increase of soil matrix suction, the permeability difference gradually decreases. In addition, the variation of the permeability coefficient of unsaturated soil was significantly affected by the percussive water content and percussive work of the soil samples. The microstructural analysis showed that wet subsidence resulted in significant changes in the pore characteristics and particle structure of loess, with the porosity decreasing from 0.374 to 0.296, the equivalent diameter decreasing to 4.028 μm, the pore morphology ratio increasing to 2.113, and the fractal dimension rising from 1.5021 to 1.5467, reflecting the increase in the pore complexity of the soil samples after wet subsidence deformation. The wetting mechanism of unsaturated loess is mainly affected by microstructure and intergranular suction, and the increase of moisture leads to the weakening of structural suction and sliding of soil particles, which in turn triggers the collapse of microstructure to form wetting. In summary, this study not only provides a new perspective for understanding and predicting the wet subsidence of loess, but also provides an important scientific basis and practical guidance for related applications in soil engineering and environmental science.