干密度及冻融循环对黄土渗透性的各向异性影响

黄土作为特殊土之一广泛分布于我国中西部季节性冻土地区，以具有明显各向异性的西安Q3原状黄土为研究对象，采用GDS三轴渗透仪测量不同干密度原状黄土竖直向及水平向渗透系数。结果表明，原状黄土水平向渗透系数大于竖直向渗透系数，水平向渗透系数和竖直向渗透系数均随干密度增大而减小；原状黄土渗透各向异性随干密度增大而增强。在封闭系统下用冻融循环箱对干密度相同而初始含水率不同的原状黄土进行冻融试验，结果表明冻融后试样水平向及竖直向渗透系数均随冻融时试样初始含水率的增大而增大；冻融后黄土渗透各向异性随冻融时试样初始含水率的增大而减弱。随着冻融次数增加，黄土水平向及竖直向渗透系数先增大然后趋于稳定；黄土渗透各向异性随冻融次数增加而显著改变，表现在黄土的水平向渗透系数与竖直向渗透系数比值随着冻融循环次数的增加而减小。最后通过观测黄土的微观结构分析了其对黄土渗透性的重要影响。

Influence of dry density and freezing-thawing cycles on anisotropic permeability of loess

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.