Thermo-Hydro-Mechanical Behavior of Argillaceous Geological Media

Argillaceous geological media, predominantly claystones and mudrocks, exhibit a tightly coupled interplay between thermal, hydraulic and mechanical processes that governs their performance in subsurface engineering applications. When subjected to heat—whether from radioactive decay, geothermal exploitation or sequestered fluids—these fine-grained formations undergo thermal expansion, pore-water pressure changes and volumetric deformation. Low intrinsic permeability and high specific surface area of clay minerals give rise to pronounced thermal pressurisation and delayed fluid transfer, while anisotropy imparted by bedding planes controls directional stiffness and fracture susceptibility. Swelling of clay phases upon re-saturation counteracts thermal contraction and may seal potential cracks, yet non-uniform temperature fields can induce shear localisation or tensile damage. Understanding the spatial and temporal evolution of temperature, saturation and stress is therefore essential for the design of deep geological repositories, enhanced geothermal systems, CO₂ storage sites and tunnelling projects. Recent advances in numerical modelling, laboratory experimentation and in situ monitoring have begun to unravel the complex feedbacks between heat propagation, fluid migration and mechanical response, informing strategies to mitigate thermal-mechanical damage and optimise barrier performance.

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Thermo-Hydro-Mechanical Behavior of Argillaceous Geological Media publication trend

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Technical terms

Thermo-hydro-mechanical coupling: Interaction among temperature changes, fluid flow and mechanical deformation in porous media.

Argillaceous media: Fine-grained sedimentary rocks rich in clay minerals and characterised by low permeability and high plasticity.

Thermal pressurisation: Increase in pore-water pressure resulting from heating under undrained conditions, potentially leading to mechanical weakening or fracturing.

Poroelasticity: Theory describing the elastic deformation of a fluid-saturated porous solid under coupled mechanical and pore-pressure loading.

Bentonite barrier: Engineered clay backfill used for its swelling and self-sealing properties in waste disposal and containment applications.

References

1. The relevance of two-phase flow in the thermo-hydro-mechanical evolution of clay formations exposed to high temperatures by heat-emitting waste. Applied Thermal Engineering (2025).
2. Modelling the Mont Terri HE-D experiment for the Thermal–Hydraulic–Mechanical response of a bedded argillaceous formation to heating. Environmental Earth Sciences (2017).
3. A study of thermal pressurization and potential for hydro-fracturing associated with nuclear waste disposal in argillaceous claystone. International Journal of Rock Mechanics and Mining Sciences (2020).