A coupled thermo-hydro-mechanical-chemical (THMC) formulation is presented. The formulation combines a THM approach already existing and operational with the equations of reactive transport in a fully coupled manner. The reactive transport equations are set in the context of an unsaturated deformable porous medium with several chemical species dissolved in the liquid phase but also present in the solid phase. Chemical reactions considered in the formulation include: i) homogeneous reactions: aqueous complex formation, acid/base and oxidationlreduction, and ii) heterogeneous reactions: dissolution/precipitation of minerals and cation exchange. Local equilibrium is assumed for all the chemical reactions except for dissolutionlprecipitation of minerals where kinetics can also be considered. Two examples of application are described. The fust one addresses the issue of scale formation around boreholes when oil production is stimulated by waterflooding. In the second one, the THMC behaviour of a bentonite engineered barrier is analyzed in the context of a large scale in situ heating test.