Study On Underground Water Pollutants Migration Based On Large Strain Consolidation Theory

ABSTRACT:Natural clay is always used as waste yard or other impermeable foundation and is prone to large strain consolidation with overlying garbage and caprock. Therefore, in the study of migration and transformation law of pollutants in the clay liner, the consolidation deformation of the clay must be considered. Firstly, a multi-dimensional large strain consolidation model of saturated clay was improved based on the microscopic model of representative elementary volume (REV). Secondly, Lagrangian and Eulerian described multi-dimensional pollutant transport model and control equations were established based on solid-liquid two-phase pollutant mass conservation law. Finally, based on COMSOL Multi-physics software platform, coupling of clay large strain consolidation and pollutant migration was stimulated and analyzed under two-dimensional condition; ALE method was used while considering large strain of the model. The simulation results were validated to be consistent with the calculation results of one-dimensional coupling theory. The law of contaminant transport and transformation were investigated then under coupling of clay large strain consolidation and pollutant migration. The effect of effective diffusion coefficient, permeability, infiltration line height of the leachate, adsorption coefficient, surface pressure loads of the landfill clay and other factors on pollutant migration were analyzed. The vertical and horizontal deformations of which were compared with the theoretical results of clay small deformation consolidation and pollutant migration theory. The main conclusions are as follows:1. Eulerian and Lagrange description for large strain consolidation and pollutant migration coupling theory has been modified, nonlinear changes of the effective diffusion coefficient is taken into account, and considering of solute potential is added in soil-water potential equation. Finally both Eulerian described and Lagrange described pollutant migration control equations are derived.2. With increasing bottom pressure load of the landfill, effect of the effective diffusion coefficient on both sides and middle of the clay layer are similar on pollutant migration depth and magnitude. With increasing load of the clay layer, the difference between large and small strain theory increases. The pollutant migration depth of large deformation theory is greater than that of small strain theory, indicating that the ability of landfill seepage under large strain analysis is weaker than that under small strain analysis.3. When pressure is applied in the same direction with the direction of the initial Darcy flow lines of the clay layer, convection mechanism triggered by the pressure has a significant accelerating effect on pollutant migration and diffusion; while with different pressure direction with the initial Darcy flow lines, accelerating effect on pollutant migration is not obvious.4. In the design of impermeable layer of the landfill, if bottom pressure load of the landfill is great, the amplification effect of permeability on pollutant migration should be considered to determine an appropriate permeability index. The amplification effect can be ignored under small pressure load.5. Under high infiltration line of leachate, the pollutant migration depth in the middle of the clay layer will be greater than those of the two sides after years, which is more obvious under increasing landfill heaping.