Hydro-Mechanical-Chemical Coupled Model for Solute Transport Considering the Influence of Entrapped Bubbles

Clay soils, usually in an unsaturated state, are widely used as barrier materials in solid waste landfills. When the saturation of clay soils is high, the gas phase will be in the form of entrapped bubbles. The entrapped bubbles can directly affect the soil hydraulic behavior, which further affects solute transport in clay liner. Therefore, based on the stress balance, fluid mass conservation, and solute mass conservation equations, and combined with the relationship between pore water pressure and air pressure in unsaturated state, a coupled hydro-mechanical-chemical model has been put forward to study the influence of entrapped bubbles on solute transport process. Using the proposed model, a series of numerical calculations are carried out through the finite element simulation software COMSOL Multiphysics. The numerical results show that the increase of entrapped bubble content can enlarge soil deformation and slow down the rates of excess pore fluid pressure dissipation and solute transport. In particular, when the degree of saturation in air phase increases from 0 to 0.2, the difference of influence depth at the transport time 10 years reaches 28 cm, and the breakthrough time of solute is prolonged by 17.8 years.