冻融循环对黄土渗透系数各向异性影响的试验研究

为了反映冻融循环作用对原状黄土渗透各向异性及原状、 重塑黄土渗透差异的影响， 以西安Q₃黄土为研究对象， 通过三轴固结渗透试验对比分析了冻融前后水平、 竖直向原状黄土及重塑黄土的渗透系数随初始含水率、 围压、 冻融循环次数变化的规律。结果表明： 未冻融时各级围压下竖直向原状黄土的渗透系数为2×10^-6 ~ 18×10^-6 cm?s^-1， 水平向原状黄土和重塑黄土的渗透系数为0 ~ 4×10^-6 cm?s^-1； 经历冻融循环后， 水平、 竖直向原状黄土及重塑黄土的渗透系数与初始含水率的关系曲线分别呈现逐渐上升、 抛物线形式与变化平缓的不同特征， 而三者的渗透系数均随冻融循环次数的增加呈现数量级增大的趋势； 原状黄土的竖直 - 水平渗透系数比（k_v /k_h ）由冻融前的4.38逐渐减小到0.90， 可见冻融循环作用在显著提高黄土渗透性能的同时， 可以强烈弱化其各向异性特征。通过建立围压、 渗透系数与土体孔隙率的相关关系可知， 原状、 重塑黄土的孔隙率与围压存在极强的负线性相关性， 渗透系数随围压的增大呈典型指数衰减特征， 渗透系数与孔隙率具有相似的变化趋势， 因此冻融循环过程中土体孔隙率的改变是导致其渗透性质变化的主要原因。

Investigation on the influence of freezing-thawing cycle on the permeability coefficient anisotropy of loess

In order to reflect the influence of freezing-thawing cycles on the permeability coefficient anisotropy of undisturbed loess and the permeability differences between undisturbed and remolded loess， Q₃ loess samples with obvious anisotropy were collected from Xi’an. Triaxial permeability tests were conducted to analyze the change law of permeability coefficient of horizontal and vertical undisturbed loess and remolded loess varying with initial water content， freezing-thawing cycles and cell pressure before and after freezing-thawing cycles. It can be obtained that before the freezing-thawing cycle， the vertical permeability coefficient of undisturbed loess is 2×10^-6 ~ 18×10^-6 cm?s^-1， while the horizontal permeability coefficient of undisturbed loess and the permeability coefficient of remolded loess is 0 ~ 4×10^-6 cm?s^-1. After the freezing-thawing cycles， the relationship curves between the permeability coefficient and the initial water content of the horizontal and the vertical undisturbed loess and remolded loess present different characteristics of gradual rise， parabola form and gentle change. However， with the increase of freezing-thawing cycles， the permeability coefficients of the horizontal and the vertical undisturbed loess and remolded loess shows an increasing trend of order of magnitude. Moreover， the ratio of vertical to horizontal permeability coefficient （k_v /k_h ） of undisturbed loess decreases from 4.38 to 0.90 gradually， which can be seen that the freezing-thawing cycles can not only improve the permeability of loess significantly， but also strongly weaken the anisotropy of loess. By comparing the correlation between cell pressure， permeability coefficient and porosity， the results show that there is a negative linear relationship between the porosity and cell pressure of the undisturbed and remolded loess. It can be explained that the change of porosity is the main reason for the change of loess permeabilityby an exponential rule of permeability coefficient and the cell pressure， as well as the similar variation curves of the permeability coefficient and porosity.