Coupled thermo/hydro/chemical/mechanical model for unsaturated soils - Numerical algorithm

This paper presents the implementation of a numerical algorithm for a new coupled thermal–hydraulic– chemical–mechanical model for unsaturated soil. A brief treatment of the theoretical development of the coupled model is presented first, with specific attention to the multi-component chemical transport theory and its cross couplings with other primary variables. The system of coupled equations is based on a mechanistic approach with conservation of mass or energy equations defining the flow behaviour and a stress–strain equilibrium equation defining the mechanical behaviour. The geochemical interactions are incorporated by linking a geochemical model with the system of coupled flow and deformation equations. Two coupling strategies, namely, sequential non-iterative and sequential iterative approaches are incorporated to link the multi-component chemical transport equation with geochemical interactions. The model’s ability is then demonstrated via a series of 1D examples, which consider complex coupling scenarios involving all the primary variables. Specifically, the effects of multi-component precipitation/dissolution and ion exchange reactions in a variable thermal–hydraulic–mechanical field are considered. The numerical efficiency of the model is also analysed based on these examples. It is concluded that the model not only provides a stable solution but is able to produce results that are qualitatively consistent with observed behaviour. Copyright q 2006 John Wiley & Sons, Ltd