A study of dispersion experiment and simulation of the cohesive layered soil in the transition zone of the Jianghan Plain

In order to study the law of solute migration in the cohesive stratified soil in the transitional zone of the Jianghan Plain-Dabie Mountain area, the conservative anion Br⁻ is taken as a tracer agent in the isothermal adsorption experiment. One-dimensional dispersion experiment and HYDRUS-1D software simulation inversion method are used, and the adsorption parameter, migration law and migration inversion dispersion parameter of Br⁻ in the cohesive stratified soil are examined. The results indicate that (1) both the Freundlich model and Langmuir model can well fit the adsorption experiment results, along with the increase of proportion of clay particle in the soil, and the saturation adsorption amount of the soil to Br^- increases. (2) Both the soil texture and structure in the stratified soil can influence the shape of the breakthrough curve, but the dispersion process in one-dimensional saturation earth pillar mainly depends on the proportion of clay particles in the water-bearing media system, and the increase of clay particles will produce resistance for solute transport. (3) The invert dispersion parameter through the HYDRUS-1D software construction model, R² is always larger than 0.991, and the fitting effect is good. The analysis results show that no matter soil component type or layer thickness and ordering in the stratified soil, the essence to influence dispersion function is by changing the average hole flow velocity of the soil, and the dispersion coefficient becomes smaller as the average hole flow velocity is smaller. (4) The silty clay dispersion coefficient in the experiment ranges from 0.005 to 0.048 cm²/d, far less than the sand dispersion coefficient 0.524 to 7.477 cm²/d in the under part, the difference value reaches two order of magnitudes, indicating that the thick layer clay soil is a control layer and will greatly resist solute transport of groundwater. The pollutant or organic matter in the upside water-bearing stratum is very hard to penetrate this layer and migrate downward, and this layer has very good sewage removal performance. The results are of great application value for groundwater environmental protection and water quality control in the transition zone of the Jianghan Plain.