Contaminant Transport Model Research Based On The Mixture Theory

Clay barriers, which are major components of landfills, have played a very important role in obstructing the contaminants of surrounding. And the design and construction of the landfill should be based on the mechanism and transport processes of contaminants in the clay barriers. Under the effect of multi-field (temperature, con-centration, seepage and deformation fields, etc.) and multi-scale structure of the clay, the interaction of contaminants and the clay barriers is complicated during the transport processes. Not only does the effect of outfield induce the transport process of contami-nant in Physical, chemical and biological aspects, but also change the inherent transport feature of the soil which will influence the contaminant transport properties. Hence, es-tablishing a multi-field coupling transport model to describe the contaminant transport process is needed. However, the conventional method is adopting the simple convec-tion-diffusion equation combining with source item which considering the chemical and biological process, to simulate the transport processes of contaminants in the clay barri-ers. The complex interaction between contaminants and the clay barriers can't be re-flected by this empirical method. However, the mixture theory, developing from sixties and seventies, is an apriori theory used to describe the complex interior interaction of the mixture and the behavior of mixture under the exogenic and environment function. The general constitutive relationship can be deduced through this theory. In this paper, the framework of multi-field coupling contaminant model was established based on the mixture theory. And the mathematical models simplified through the framework were calculated and analyzed. The study contained the following main parts.1. The soils of the barriers were considered as a mixture composed of the clay min-eral, the adsorptive fluids and bulk fluids. The thermo-hydro-chemo-mechanical con-taminant transport model was established on the mixture theory. The internal variables were induced in the model to consider the plastic response of the soils. The mass trans-fer effect between adsorptive fluid and bulk fluid, the phenomenon of coupling transport and the influence of the thermo-hydro-chemo-mechanical coupling effect on the inher-ent transport property can be considered in this model.2. The mixture theory of multicomponent micropolar porous media was constructed by considering the micropolar behavior of the soil material. The mass exchange in the mixture was not considered for simplifying. The general stress-strain constitutive rela- tionship, Darcy's law, Fick's law and Fourier's law of this micropolar mixture were ob-tained.3. The 1D contaminant transport mathematical model for the nonchemical reaction soils, considering the hydro-mechanical effect on the coefficients of seepage and diffu-sion, was established on the simplified framework. The mathematical model was non-dimensionalized and computed with the Crank-Nicolson finite difference method. Pa-rametric analysis was developed according to calculate the contaminant concentration distribution in the barriers under the different advection-consolidation number.4. The 3D contaminant transport mathematical model considering the hy-dro-mechanical effect on the coefficients of seepage and diffusion was established di-rectly toward the target of simulating the contaminant transport process existed circle defects in geomembrane. The stress-strain response of the soils was described with the ALPHA-SMP elastoplastic constitutive model. The computation of the model was real-ized by the secondary development of ABAQUS. The contaminant concentration dis-tribution under the different sizes of the defects was compared.5. A one-dimension mathematical hydro-chemo-mechanical contaminant transport model was established according to the theoretic framework. The influence on the in-herent transport nature under the hydro-chemo-mechanical coupling effect was consid-ered based on the change of macroscopic porous. The computation of the mathematical model was based on the coupling advection and diffusion flux.The parameter analysis about consolidation load, diffusion-consolidation coefficient, coupling deformable ef-fect, effective osmotic coefficient was progressed. The influence of the thermo-hydro-chemo-mechanical coupling effect on the inherent transport property was considered with the changing of macroscopic porous. The computation of the mathe-matical model was based on the coupling advection and diffusion flux. The parameter analysis about consolidation load, diffusion-consolidation coefficient, coupling de-formable effect, desorption effect and effective osmotic coefficient was progressed.6. A one-dimension mathematical thermo-hydro-chemo-mechanical contaminant transport model was established according to above thermo-hydro-chemo-mechanical theoretic framework. The influence of the thermo-hydro-chemo-mechanical coupling effect on the inherent transport property was considered with the changing of macro-scopic porous. The computation of the mathematical model was based on the coupling contaminant advection, diffusion and heat flux. The parameter analysis about heat-consolidation, thermo-chemical desorption effect, heat-osmotion and heat-diffusion coefficient was progressed.