GAS-WATER TWO-PHASE DIFFUSION MODEL FOR UNSATURATED LAYERED COVER SYSTEMS

A one-dimensional diffusion model of gas is developed to investigate landfill gas transport in unsaturated layered cover systems. Coupled processes of gas diffusion in the unsaturated cover and transient water transport in the media were considered. The mathematical model was solved by using the finite element analysis software COMSOL Multiphysics 4.3. The results obtained by the proposed model agree well with those obtained by the experimental methods. It is shown that the variation of water content has great influence on landfill gas transport in a 1-meter-thickness unsaturated landfill cover soil. For the 1-meter-thcikness unsaturated cover soil, the relative gas concentrations for the case assuming coupled transport was approximately 8 times smaller than those assuming steady transport at the time range of 20 d to 100 d. It is indicated that the water content is of great importance when predicting the unsteady gas migration in unsaturated landfill cover systems.