Investigation into microscopic mechanisms of anisotropic saturated permeability of undisturbed Q₂ loess

The anisotropic permeability of loess is an important engineering property. To explore the microscopic mechanisms of anisotropic saturated permeability of undisturbed loess, a series of laboratory tests, including constant-head saturated permeability test, particle size analysis, and scanning electron microscope imaging, were carried out for twelve Q₂ loess samples. The results show that with increasing burial depth, the saturated permeability decreases. Increasing the hydraulic gradient leads to an increase in permeability without changing the anisotropy of permeability. The spatial variability of the vertical permeability is more obvious than that in the horizontal direction. In addition, the permeability is negatively correlated with the clay particle content, and the uniformity coefficient of the particles. The area of the pores is the dominant factor controlling the permeability, especially the extra-large pores. Moreover, the direction and morphology of pores also affect the permeability of undisturbed loess. These findings are helpful for better understanding the water infiltration process in undisturbed loess and for investigating the stability of loess slopes.