A novel numerical approach for the modelling of Thermo-Hydro-Mechanical (THM) processes in the vicinity of a Geological Disposal Facility (GDF) for the long-term storage of radioactive waste is presented. This work is based on a dual numerical code framework with a multiphase flow solver for thermo-hydraulic processes and a geo-mechanical solver for mechanical processes in fractured and fracturing rock masses. The method has a unique continuum-discontinuum configuration that allows each of the THM processes to be represented with the most suited formulation, thus improving the accuracy and complexity of the simulations. Thermal processes are implemented within the geo-mechanical solver using both an explicit and an implicit approach, the latter allowing the modelling of temperature over large time scales, an important feature in the context of geological disposal. Moreover, a novel thermal contact approach is presented to investigate the heat transfer between contacting solids and its application to heat transfer across fractures is discussed. Furthermore, a thermo-mechanical coupling formulation is derived in the geo-mechanical solver, enabling thermal expansion and thermally induced fracturing. Then, the THM coupling is finalised using a conservative projection method that enables information exchange between superimposed numerical meshes e.g. heat transfer between the thermo-hydraulic and the thermo-mechanical solvers. Both applications in porous media and with laminar flow are explored. Finally, the THM dual framework is applied to the modelling of thermal spalling occurring in the excavation walls of a deposition hole in a GDF. The potential of the method to offer new predictive capabilities and insights on unexplained experimental observations is demonstrated by considering the concurrence over time of THM factors influencing spalling, especially multi-phase flow in the continuum and explicitly represented fractures in the discontinuum.