Abstract: As a kind of special soil, loess is widely distributed in seasonally frozen regions. The test samples are the undisturbed Q3 loess with obvious anisotropy from a building site in Xi’an city. The saturated hydraulic conductivity of undisturbed loess considering the influence of density is measured by triaxial permeability apparatus GDS. It can be obtained that the hydraulic conductivity in horizontal is higher than that in vertical. The saturated hydraulic conductivity decreases with the increase of density. However, the anisotropic permeability of undisturbed loess increases with the increase of density .The loess, which has the same density but a different initial moisture content, experiences freezing-thawing cycles in an closed system. The results show that the saturated hydraulic conductivity of the samples, which has experienced freezing-thawing cycles, increases with the initial moisture content increasing. However, the anisotropic permeability of loess experiencing freezing and thawing reduces with the initial moisture content increasing. The saturated hydraulic conductivity increases first, then reaches a steady state with increasing freezing-thawing cycles. However, the anisotropic permeability of undisturbed loess changes significantly with increasing freezing-thawing cycles. The ratio of loess permeability decreases significantly with the increase of freezing-thawing cycles. The test results indicate that the anisotropy of loess structure has a significant effect on the anisotropic permeability. Meanwhile, Freezing-thawing changes the permeability of loess by changing its microstructure.

Key words: undisturbed loess, permeability, anisotropy, dry density, freezing-thawing cycles, microstructure