多孔介质界面对重非水相液体迁移过程影响的图像法研究

Investigation on the influence of porous media interface on DNAPL migration based on image methods

重非水相液体(dense nonaqueous phase liquid,DNAPL)污染土壤和地下水的问题已引起广泛关注,研究其在不同粒径多孔介质及其界面的运移特征形态是确定污染区域、修复治理土壤和地下水环境的前提。文章通过室内试验研究多孔介质界面对DNAPL运移与分布特性的影响。首先在二维砂槽上进行DNAPL污染物的入渗试验,试验过程中用数码相机拍照,将DNAPL扩散过程以图像的形式记录下来;然后用AutoCAD对图片进行处理,绘制出DNAPL迁移过程的锋面变化图。结果表明:DNAPL入渗过程中,迁移主要受到重力作用与毛细作用的控制,毛细作用力随着介质粒径的增大逐层减小,重力作用逐渐起主导作用使污染物入渗速度逐层增大;介质结构影响DNAPL的迁移形态,介质粒径逐层增大,DNAPL污染物的渗流面与指进扩散宽度逐层减小,扩散方式由面状变为指状;在不同粒径介质界面介质结构发生突变时,DNAPL迁移锋面线曲率也相应变大,此时DNAPL的迁移呈现“凸”型特征,另外,不同的界面横向扩散的滞留宽度不同,随着介质粒径的增大,界面的横向扩散宽度相对变短。

The problem of dense nonaqueous phase liquid(DNAPL) polluting soil and groundwater has attracted extensive attention. The study of the transport characteristics of porous media with different particle sizes and their interfaces is the premise for determining the pollution area and repairing the groundwater environment. The effects of porous media interface on the migration and distribution of heavy non-aqueous liquids (DNAPL) are investigated by laboratory experiments. DNAPL infiltration experiment is conducted in a 2-D sand tank and pictures are taken to record the diffusion process using the digital camera. The image is processed with AutoCAD to draw DNAPL migration and the infiltration frontal variation pictures in different times are obtained. The results show that during the process of DNAPL infiltration,the migration is mainly controlled by gravity and capillary action. The capillary force decreased with the increasing particle size of the media,and the gravity plays a leading role in increasing the infiltration rate of the pollutants. The medium structure affects the migration pattern of DNAPL.The particle size of the medium increases layer by layer,the percolation area and the diffusion width of the DNAPL contaminant decrease layer by layer,the diffusion mode changes from planar to finger.When the interface structure is abrupt,the curvature of the DNAPL migration front line is correspondingly larger.At this time,the migration pattern of DNAPL exhibits a “convex” shape.In addition,different interfaces have different retention widths for lateral diffusion.As the particle size of the medium increases,the lateral diffusion width of the interface becomes relatively short. The results are of important practical significance for the evaluation of DNAPL contamination and the restoration of contaminated sites.