Study On The Diffusion Law Of Contaminants Under The Influence Of Semi-Boundary Conditions And Consolidation

China and the world are facing very serious soil pollution problems.As an economic and effective way,pollutant repository is often used to treat industrial and agricultural pollutants.Diffusion,as one of the important components in the migration of contaminant,dominates the migration process when the contaminated storage medium has low head and low hydraulic conductivity.The process of the diffusion of the contaminated is often accompanied by consolidation due to the overburden load and the capping layer load,which will inevitably affect the diffusion.Numerical simulation is very complicated when dealing with related problems,and it is particularly important to develop corresponding analytical solutions.Proposes a semi-diffusion boundary condition control method based on the boundary conditions required by the above-mentioned different engineering backgrounds.The influence of different consolidation theories on the diffusion of contaminant in the capping system is considered.The main research contents and result are as follows:(1)Based on the governing equation for the diffusion of contaminant in the contaminated medium,an analytical solution for the one-dimensional diffusion of contaminant concentration in a single contaminated soil layer under semi-diffusion boundary conditions is proposed.And further obtained the analytical solutions of the degree of diffusion and mass flux in the contaminated soil layer.The results obtained by using COMSOL numerical simulation and the existing analytical solution results are compared and verified with the analytical solution results in this paper.The sensitivity of related parameters is analyzed based on different semi-diffusion boundary combinations.The results show that different semi-diffusion boundary factor combinations have a great influence on the concentration of contaminant in the contaminated soil layer.The larger the semi-diffusion boundary factor,the lower the concentration of contaminant within the corresponding boundary,the degree and rate of diffusion will getting higher,he greater of diffusion flux at the boundary of the contaminated soil layer within a certain period of time,and the faster the flux decreases with the reduction of difference in contaminant concentration.(2)It further considers the diffusion law of contaminant in each layer of contaminated soil when there are differences in the properties and diffusion capacity of the soil layer due to layering.An analytical solution for one-dimensional diffusion of contaminant concentration in double-layer contaminated soil under semi-diffusion boundary conditions is proposed.And further obtained the analytical solution of the degree of diffusion and flux of each layer.The results obtained by using COMSOL numerical simulation are compared and verified with the analytical solution and the sensitivity of related parameters is analyzed.The results show that the contaminant concentration in each layer of contaminated soil not only decreases with the increase of the semi-diffusion boundary factor,but also with the increase of the difference between the upper and lower semi-diffusion boundary factors,the difference in the concentration distribution slope at the junction of the two contaminated soil layers also increases.It has obvious inflection point at the junction.The larger the semi-diffusion boundary factor,the faster the concentration of contaminant in the corresponding contaminated soil layer will decrease,the higher the degree and rate of diffusion that has occurred,the greater the diffusion flux at the boundary of the contaminated soil layer within a certain period of time,and the rate at which the mass flux will decrease faster.(3)A one-dimensional diffusion model of contaminant in the compressible contaminated sedimentary layer and its capping system under the influence of consolidation in disjointed rivers is proposed.Based on the theory of small deformation,large deformation,and nonlinear consolidation compression,the analytical solutions of one-dimensional diffusion in the contaminated sediments were obtained.Further consider the analytical solution of the one-dimensional diffusion of contaminant in the overlying capping layer due to the failure of the barrier layer.The results obtained by COMSOL numerical simulation and the existing analytical solution results was compared and verified with the analytical solution results of this paper.The results show that the concentration of contaminant in the sedimentary layer and capping layer changes significantly under the influence of consolidation,which is higher than the concentration without considering consolidation.The diffusion mass flux of contaminant under the influence of consolidation obtained by different consolidation theories has a certain degree of increase.Among them,the effect of the large deformation consolidation theory are the most obvious,and the effect of the small deformation and nonlinear theories are relatively similar.