The permeability of unsaturated loess is an important part of its properties. The research on loess permeability in different directions is particularly important to determine the range of loess collapse and the study of loess landslides caused by the infiltration of water in the loess. So

the anisotropic permeability and mechanism of Q3 loess are studied. The test samples are the undisturbed Q3 loess with obvious anisotropy from a building site in Xi’an city. The matrix suctions at different volumetric water contents and in different directions are measured with tensiometer. The saturated hydraulic conductivity is measured by falling head permeability test. The results show

while tensiometer is inserted vertically and paralleling with soil layer into samples

that the suctions are very close as the volumetric water content is between 0.23 and 0.41; and the saturated hydraulic conductivity in vertical direction is 4.02 times as that in horizontal direction. Further

the correlation function between the hydraulic conductivity and suction for unsaturated loess in vertical and horizontal directions is obtained by the soil-water characteristic curve based on the measured suctions. It can be obtained that the hydraulic conductivity reduces/increases with the matrix suction increases/reduces in both directions of the loess. The hydraulic conductivity in vertical is generally higher than that in horizontal. The difference of hydraulic conductivity between vertical and horizontal directions reduces with the matrix suction increases when matrix suction is less than 57 kPa. Structure observation shows that the anisotropy of loess structure has a significant effect on the anisotropic permeability.