| Due to the complexity ? spatial variability and multiscale of porous media,the mechanism of contaminant transport and quantitative calculation in porous media is still an important research direction in the field of hydrogeology.On the basis of collecting and sorting out the domestic and foreign relevant research on the study of porous media,a long 200 cm,wide 10 cm,high 3cm organic glass body was designed,in which quartz sand with different size and quartz sand,white onyx and glass beads with different circular curvature were filled respectively,also brilliant blue was used as a tracer to simulate the water flow and solute transport behavior of porous media.The method of digital imaging and Matlab image processing technology were used to analyse image correction.A quantitative relationship between the concentration and the RGB image of the brilliant blue was also established to determine the solute concentration.We not only make the breakthrough curve of concentration versus time at a certain distance,but also make the breakthrough curve of concentration versus distance at a certain time,and then the analytical solution of ADE model was used to simulate the breakthrough curve respectively to get a better understanding of the temporal and spatial variation of pollutants.In addition,the quantitative relationship between the dispersion coefficient D and the velocity v under different conditions was studied in detail.We not only analyze the influence of the particle properties on the relationship,but also study the influence of the laboratory scale.The influence factors,rules of water flow and solute transport in porous media are summarized as follows:(1)A real time monitoring technique for the transport of porous media was developed,which had high accuracy,also the accuracy of the method was compared with the sampling method.Through the experiment,it was found that the correlation coefficient R2 was 0.9964,which showed that the method had high precision,and also solved the problem that the traditional sampling detection method often led to the problem that the quality of the pollutant was not conserved.(2)The relationship between the average velocity of groundwater and the hydraulic gradient was consistent with the traditional Darcy's law.Through the hydraulic experiment,we found that the velocity of v was linear with the hydraulic gradient J,also the value of linear correlation coefficient R2 was higher,and the correlation coefficient was greater than 0.99 under different experimental conditions.(3)Under different experimental conditions,the breakthrough curves of concentration of pollutants versus time and concentration versus distance were obtained,the advection-dispersion equation was established,and the analytical solution was obtained.It was found that although the overall accuracy of the breakthrough curve and the model fitting was good in the different simulated media under Darcy flow,the phenomenon of early arrival and tailing were both found,that was,the phenomenon of Non-Fickian,also this phenomenon was more obvious with increasing particle size and decreasing circular curvature.(4)The values of dispersion coefficient D decreased with increasing particle size?decreasing circular curvature ? increasing flow velocity or increasing migration distance.This showed that there was a certain scale effect in dispersion coefficient.(5)It was found that there was an obvious double logarithmic linear relationship between the dispersion coefficient D versus the flow velocity v,and the relationship could be expressed as D=?v?,also the index values of ? was in the range of 1.0358-1.2327 in this study,all was among 1.0-2.0.It approached to a value of 1.0 with decreasing particle size?increasing circular curvature or travel distance.It was shown that the value of ? was not only related to the properties of the particles,but also had a certain scale effect. |
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