New coupled Thermo-Hydro-Mechanical-Chemical formulations with consideration of swelling and dissolution

This thesis fundamentally extends the new theory, Mixture-Coupling Theory (MCT), to develop a new Thermo-Hydro-Mechanical-Chemical model by including swelling (e.g., hydration) and dissolution in soils/rocks, with the engineering application focusing on nuclear waste disposal.

The Mixture-Coupling Theory is based on non-equilibrium thermodynamics and continuum mechanics. This thesis firstly builds an advanced Hydro-Mechanical (HM) coupled model by incorporating the swelling and dissolution influence. The model is then extended to unsaturated conditions. Afterwards, the unsaturated Hydro- Mechanical-Chemical (HMC) model is developed, and finally, a new coupled Thermo- Hydro-Mechanical-Chemical (THMC) formulation with consideration of swelling and dissolution is derived. All the numerical simulations in this thesis are for demonstration purpose with application in the field of nuclear waste disposal.

Deep geological disposal is a major approach to treat high-level nuclear waste, in which the nuclear waste is isolated in the deep geological rock formation at a depth of hundreds of meters or several kilometres below the surface. The waste is kept away from the biosphere by a multi-barrier system consisting of artificial barriers (bentonite, concrete, et al.) and the natural surrounding rock. The swelling of backfill bentonite and clay-rich rock, and the chemically induced reaction (e.g., dissolution) have a significant influence on the integrity and stability of the engineered barriers and significantly affect the THMC process.

The new coupled Thermo-Hydro-Mechanical-Chemical (THMC) model with consideration of swelling and dissolution achieves a deeper understanding of the rock/clay behaviour of the multi-barrier system and provides a more realistic prediction for nuclear waste disposal safety assessment.