均质与非均质土中水动力弥散规律研究

Study of Hydrodynamic Dispersion Laws in Homogeneous and Heterogeneous Soil

为探究均质与非均质土中溶质迁移扩散的一般性规律,通过室内柱试验对不同条件下的水动力弥散现象进行观察监测。并利用经典的对流扩散(ADE)模型拟合分析相应的溶质穿透曲线。结果表明:在均质土中溶质浓度对水动力弥散系数和穿透曲线的影响甚微;而溶质迁移流速对水动力弥散具有促进作用,流速越大,水动力弥散系数越大,穿透曲线完成时间越快;同一流速下,水动力弥散系数与砂土的平均粒径存在正相关关系,且平均粒径越大的砂土,受流速影响越大。此外,土壤中溶质迁移扩散时存在明显的尺度效应,一般迁移距离越远溶质水动力弥散系数越大。与均质土壤介质相比,层状土壤的非均质性及不同层状结构对水动力弥散作用更为显著。

To investigate the general laws of solute transport in homogeneous and heterogeneous soil, this study conducts column experiments in the laboratory to observe and monitor hydrodynamic dispersion under different conditions.The measured breakthrough curves of solute are fitted and analyzed by the classical advection-diffusion equation(ADE).The results reveal that the solute concentration has little effect on the hydrodynamic diffusion coefficient in homogeneous soil;however, the flow rate of solute transport can promote hydrodynamic diffusion, namely that a higher flow rate can lead to a larger hydrodynamic diffusion coefficient, and the breakthrough curves can be completed faster.There is a positive correlation between the hydrodynamic diffusion coefficient and the mean particle size of the sand at a certain flow rate.In addition, the scale effect is prominent in the solute transport process in soil;generally, the hydrodynamic diffusion coefficient increases with the traveling distance.Compared with the case of homogeneous soil, the heterogeneity and different layered structures of layered soil have a more significant influence on hydrodynamic dispersion.