This thesis is of the cumulative form, i.e. four peer-reviewed journal publications documenting the research are presented here (see appendices D through G). The sections leading up to the journal publications aim to provide a framework and context for the reader, in which the aforementioned journal publications should be seen: Eyes set on this goal, the thesis starts out by introducing the context of deep geological disposal of heat generating nuclear waste in argillaceous host rock formations, the particularities of argillites as host rock as well as the modelling concept including the theory of porous media. Next, a derivation and discussion of the principal partial differential equations governing the conservation of mass, energy and momentum as well as of constitutive laws is provided. A discussion and conclusion are presented in order to finalise the framing of this thesis. The research questions in this thesis have three focus points: First, the validity (and limits of validity) of the given thermo-hydro-mechanical conceptual modelling approaches and associated assumptions is explored. Second, the numerical implementations are thoroughly tested and demonstrated. Third, the system behaviour of deep geological repositories in argillaceous host rocks is investigated.:List of Figures IV List of Tables IV 1 Introduction p. 1 2 Research questions p.2 3 Disposal in argillaceous host rock p.4 3.1 Formation and properties of relevant argillites p.4 3.2 Barrier integrity p.5 3.3 Physical processes in deep geological radioactive waste disposal p.6 3.3.1 Thermal processes p.7 3.3.2 Hydraulicandaeraulicprocessesp.8 3.3.3 Mechanical processes p.8 3.3.4 Chemicalandbiologicalprocessesp.10 3.4 Process couplings p.10 3.4.1 Thermo-mechanical coupling p.10 3.4.2 Hydro-mechanical coupling p.11 3.4.3 Thermo-hydraulic coupling p.12 3.4.4 Aero-hydraulic coupling p.13 4 Modelling approach p.13 4.1 Concept of porous media p.13 4.2 Process equations p.15 4.2.1 Capillary pressure p.15 4.2.2 Component mass balance p.16 4.2.3 Solid mass balance p.19 4.2.4 Hydraulic constitutive laws p.22 4.2.5 Momentum balance p.29 4.2.6 Energy balance p.32 4.3 Numerical solution of process equations p.35 5 Summary of results p.36 6 Conclusion and outlook p.46 References p.47 Appendix A: Further peer reviewed publications p. 60 Appendix B:Technical reports p. 61 Appendix C: Conference contributions p. 62 Appendix D: Pitz et al. (2023a) p. 67 Appendix E: Pitz et al. (2023b) p. 88 Appendix F: Pitz et al. (2024a) p. 113 Appendix G: Pitz et al. (2024b) p.128