Integrated Experimental and Numerical Investigations on the Thermo-Hydro-Mechanical Behavior of Clays and Argillaceous Rocks: A Perspective

Over the past decade a coordinated research programme has been carried out to characterise, model and predict the coupled thermo-hydro-mechanical behaviour of clays and argillaceous rocks across laboratory, intermediate and field scales. The work spans high-precision triaxial tests on compacted bentonites and stiff claystones, multi-year heating experiments in underground research laboratories, and full three-dimensional finite-element simulations of repository cells, energy piles and climate-sensitive slopes. A family of critical-state based constitutive models is presented that unifies temperature-dependent elasto-plasticity, viscoplastic creep, suction hysteresis and structure degradation within a single thermodynamically consistent framework. The models are implemented in an implicit, fully coupled THM code and calibrated with a Bayesian workflow using sensor data from instrumented tunnels, boreholes and surface observatories. Key outcomes include: (i) explanation of anisotropic tunnel convergence driven by delayed thermo-swelling; (ii) quantification of permeability changes in excavationdamaged zones subjected to sustained heating; (iii) identification of critical suction thresholds for desiccation cracking and heterogeneous rebound in expansive strata; and (iv) demonstration of cyclic thermal effects on the shaft capacity of energy foundations. The resulting design charts and digital twins provide practical guidance for nuclear-waste repository layouts, geothermal retaining walls and slope-stability assessments under a warming climate. The paper synthesises these findings into a transferable modelling strategy that couples physics-based formulations with data-driven updating, setting the stage for next-generation THM analyses that incorporate chemical reactions, real-time monitoring and probabilistic performance evaluation.