LNAPLs迁移的数值模拟和土壤介电性质的变化分析

Numerical simulation of LNAPLs migration and analysis on variation of soil dielectric properties

包气带是地面以下潜水面以上的地带,由非饱和多孔介质构成.LNAPLs泄漏到土壤中后会对包气带和地下水造成严重污染.为了准确探测出LNAPLs的迁移范围,有必要对其迁移规律及迁移对土壤介电常数的影响进行研究.本文从扩散方程出发,采用数值模拟研究了LNAPLs泄露速率对其在包气带中迁移的影响,分析了LNAPLs迁移过程中土壤相对介电常数的变化特征.研究结果表明,LNAPLs在土体中的迁移范围受到渗漏速率的影响:对于均匀渗漏,渗漏速率越大,迁移范围越大;对于非均匀渗漏,单位时问内渗漏量一定时,LNAPLs在土体中的扩散范围短期内受到渗漏速率非均匀性的影响,但长期内并不受此影响.LNAPLs的泄露会使区域中土壤相对介电常数发生变化:在毛细水带以上的非饱和区域,相对介电常数变化较小,但由于LNAPLs的扩散,驱使土壤中残余水向两侧迁移,进而形成明显的"山形";在毛细水带,相对介电常数随LNAPLs量的变化而明显变化,并有明显的横向变化趋势.

The vadose zone, constituted by the unsaturated porous media, is the part of Earth between the land surface and the top of the phreatic zone. LNAPLs can pollute the vadose zone and the groundwater after it leaking into soil. In order to detect the position where the LNAPLs migrates to accurately, it is necessary to research the LNAPLs migration mechanism and to analyze its influences to soil relative dielectric constant. Based on the diffusion equation, this paper uses numerical simulation method to study the influence of leakage rate on LNAPLs migration in vadose zone. At the same time, we analyze the variation characteristics of relative dielectric constant in the process of migration. The results show that, the scope of the migration of LNAPLs in soil is affected by the leakage rate： for uniform leakage, the faster the leakage rate, the wider the diffusion rang; for non-uniform leakage, in the case of a certain amount of total leakage in per unit time, it is obvious that the diffusion rang are affected by the non-uniform leak rate in short term while it is unobvious in long term. Because of LNAPLs＇ leakage, the soil relative dielectric constant will change： in the unsaturated area above the capillary water zone, the relative dielectric constant is influenced a little, but because of the diffusion of LNAPLs, the residual water in soil is pushed to both sides of the area, thereby forming a clear‘mountain’; it is apparent near the capillary water zone, besides there will be a visibly lateral variation trend as time goes on.