Study On Anisotropic Permeability Of Loess Considering Density And Freezing-Thawing Effect

The strength, deformation and stability of loess are closely related with the moisture migration in loess. However, the loess moisture is changing with external factors. It is significant to research anisotropic permeability of loess on ascertaining the moisture migration. However, there are few studies on the anisotropic permeability of loess so far. This paper focus on investigating the influence of density and freezingthawing cycles on anisotropic permeability of loess.The saturated hydraulic conductivity of undisturbed loess considering the influence of density is measured by the instrument of unfirmed water head permeability test. It can be obtained that the saturated hydraulic conductivity in horizontal direction is 1.5~3.5 times as that in vertical direction.The saturated hydraulic conductivity decreases with the increase of density. However, the anisotropic permeability of undisturbed loess increases with the increase of density. The volumetric water content and matrix suction of undisturbed loess is measured by the pressure plate extractor. Further, the correlation function between the permeability coefficient and suction for unsaturated loess in vertical and horizontal directions is obtained by the soil-water characteristic curve based on the saturated hydraulic conductivity. The anisotropic permeability of undisturbed loess decreases with the matrix suction increase. The results of SEM indicate that the anisotropy of loess structure has an effect on the anisotropic permeability. In the condition of high saturation and low suction, loess microstructure has a significant impact on its permeability. The effect of loess microstructure on its permeability decreases with the matrix suction increase.The loess,which has the same density but a different initial moisture content,experiences freezing-thawing cycles in 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 freezingthawing cycles. The ratio of loess permeability decreases significantly with the increase of freeze-thaw cycles. The test results indicate that the anisotropy of loess structure has a significant effect on the anisotropic permeability. The results of SEM indicate that freezing-thawing changes the permeability of loess by changing its microstructure.