非饱和透明土优先流迁移规律分析

为实现土的非饱和优先流迁移可视化，设计立柱装置进行非饱和渗流试验，采用透明土与数字图像处理技术，建立归一化像素强度与透明土饱和度的关系，在此基础上，通过室内模型试验，研究优先流路径连通性与相邻优先流路径旋转角对非饱和土优先流迁移的影响。试验结果表明：基于图像灰度像素强度表征非饱和透明土饱和度方法是可行的；全连通优先流（O-O型）与上连通优先流（O-C型）剖面呈现T型，中心轴剖面饱和度与边缘差异明显，下连通优先流路径（C-O型）中土体油压与基质势不足以使流体进入优先流路径形成优先流，入渗趋势与均匀流一致，O-C型优先流的稳定入渗率和湿润锋推移速度分别为C-O型的1.5倍和1.4倍；相邻O-C型优先流之间区域形成新的优先流，土体达到较高饱和度，增长速率随旋转角的增加而减小，优先流转角为90?、60?、30?时稳定入渗速率分别为均匀流的1.5、1.3、1.2倍；流体受重力影响，转角小的优先流仅沿路径一侧水平渗透，但湿润锋推移速度分别为均匀流的1.3、1.4、1.5倍，相邻优先流相互作用减弱，难以形成新的优先流。

Analysis of preferential flow migration in unsaturated transparent soil

In order to realize the visualization of unsaturated preferential flow migration of soil, a column device was designed to carry out unsaturated seepage tests. The transparent soil and digital image processing technology were used to establish the relationship between the normalized pixel intensity and the saturation of transparent soil. On this basis, the effects of the connectivity of the preferential flow path and the rotation angle of the adjacent preferential flow path on the preferential flow migration in unsaturated soils were studied by conducting laboratory model tests. The results showed that it was feasible to characterize the saturation of unsaturated transparent soils based on the intensity of image gray pixels. The profile of fully connected preferential flow (O-O type) and upper connected preferential flow (O-C type) presented T-shape. The saturation of the central axis profile was obviously different from that of the central edge profile. In the lower connected preferential flow path (C-O type), the soil oil pressure and matrix potential could not make the fluid enter the preferential flow path to form the preferential flow, in which the change of infiltration was consistent with the uniform flow. The stable infiltration rate and the wetting front moving velocity of O-C preferential flow were 1.5 times and 1.4 times of those of the C-O type, respectively. A new preferential flow was formed in the area between adjacent O-C preferential flows. The soil in that area reached higher saturation and the growth rate of saturation decreased with the increase of rotation angle. When the preferential flow rotation angle was 90?, 60? and 30?, the stable infiltration rate was respectively 1.5 times, 1.3 times and 1.2 times that of the uniform flow. As the fluid was affected by gravity, the preferential flow with a small rotation angle only infiltrated horizontally along one side of the path. However, the moving velocity of the wetting front was 1.3 times, 1.4 times, and 1.5 times that of uniform flow, respectively. The interaction between adjacent preferential flows was weakened, so it was difficult to form the new preferential flow.