Geomechanical and coupled THM modelling

Geomechanical and coupled Thermo-Hydro-Mechanical (THM) modelling

The construction, operation and emplacement of radioactive waste in the underground repository will induce complex coupled thermal, hydrological, mechanical perturbation within and around these repositories.

• For instance, the underground excavation will lead to changes in the host rock surrounding the excavation, resulting in localized mechanical deformation, alteration in the stress distribution and changes in the water flow and hydraulic properties of the host rock.
• The heat generated by heat emitting radioactive waste will dissipate in all directions in the repository site and result in changes in temperature distribution in the surrounding host rock.
• This temperature variation will further modify the hydraulic properties of the host rock (increase the permeability for example) and compress the water due to the differential thermal dilation between water and host rock.
• Moreover, the temperature variation can also induce volume changes of the rock mass. Other processes, such as desaturation/resaturation, vaporaziation/condensation can occur as well.

All these thermo-hydro-mechanical processes are strongly coupled, interacting with each other in a complex manner in a radioactive waste disposal system. They also evolve in time and space as illustrated in the following figure referring to the supercontainer concept.

In addition to in-situ and laboratory experiments, numerical modelling is required for learning and understanding more about such complex perturbations caused by both the excavation operation and the heat generated by the radioactive waste. The computer codes for the numerical modelling should take into account the coupled THM mechanism.

Numerical modelling of the THM processes is intensively carried out in our research. The main applications are the following ones:

• Performance and Safety Assessment: modelling the future evolution of a site with emphasis on how this evolution affects the safety functions.
• Repository design: modelling the THM responses of the host rock, to optimize the concept of the engineered barriers.
• Interpretation of laboratory and in-situ experiments: comparison the experimental and modelling results to give support for the interpretation of the tests (OPHELIE mock-up test).
• Optimization of future in-situ experiments: predictive modelling to optimize the set-up of the in-situ experiments and the instrumentation for monitoring. The figures below show results of THM modelling of the PRACLAY heater test.

Contact: Li Xiang Ling