This study presents a fully coupled thermo-hydro-mechanical (THM) constitutive model for clay rocks. The model is formulated within the elastic-viscoplasticity framework, which considers nonlinearity and softening after peak strength, anisotropy of stiffness and strength, as well as permeability variation due to damage. In addition, the mechanical properties are coupled with thermal phenomena and accumulated plastic strains. The adopted nonlocal and viscoplastic approaches enhance numerical efficiency and provide the possibility to simulate localization phenomena. The model is validated against experimental data from laboratory tests conducted on Callovo-Oxfordian (COx) claystone samples that are initially unsaturated and under suction. The tests include a thermal phase where the COx specimens are subjected to different temperature increases. A good agreement with experimental data is obtained. In addition, parametric analyses are carried out to investigate the influence of the hydraulic boundary conditions (B.C.) and post-failure behavior models on the THM behavior evolution. It is shown that different drainage conditions affect the thermally induced pore pressures that, in turn, influence the onset of softening. The constitutive model presented constitutes a promising approach for simulating the most important features of the THM behavior of clay rocks. It is a tool with a high potential for application to several relevant case studies, such as thermal fracturing analysis of nuclear waste disposal systems. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

We present a novel multiscale framework that integrates the single -point multiphase material point method (MPM) and the discrete element method (DEM) to model the complex freeze -thaw behavior of ice -bonded granular media. The proposed numerical framework is featured by (a) employing the continuum -based MPM to solve the macroscopic governing equations for granular systems involving thermo-hydro-mechanical (THM) coupling and phase transitions, and (b) using the grain -scale discontinuum-based DEM to capture the thermodynamically sensitive mechanical behaviors of ice -bonded granular media. The multiscale framework is constructed by attaching a DEM-based representative volume element (RVE) at each material point in MPM. This RVE serves as a live sample of each material point to track the state -dependent effective stress with respect to the local deformation and thermodynamic conditions like ice saturation, bridging the macroscopic phenomena and the underlying microstructural evolution. In particular, we implement a semiimplicit staggered integration scheme for the macroscale THM-coupled MPM to boost computational efficiency and enhance numerical stability. We also propose an innovative ice saturation -dependent bond contact to effectively reproduce the thermodynamically sensitive mechanical behaviors. The new multiscale framework is first benchmarked against analytical solutions for 1D non -isothermal consolidation problems. We then demonstrate its exceptional capability in simulating intricate freeze -thaw behavior of granular media through a boundary value problem involving cyclic freeze -thaw actions. Further cross -scale analyses reveal its potential in capturing key loading- and state -dependent THM responses with explainable microstructural mechanisms during complex freezing and thawing loading conditions.

In the global warming trend, the permafrost area is decreasing. And the change of temperature seriously affects the safety and stability on Open-pit slope under the alternation of freezing and thawing. Based on FLAC(3D), the simplified algorithm of THM coupling with phase change is developed and upgraded again. The change law of failure area in one time freezing and thawing and various stability influence factors of the permafrost slope were discussed by yielding approach index. The results show that the frozen slope is local failure, from April to July is danger every year, and that the freezing temperature increment and the height of slope are still the main influence factors and that the water content, the times of freeze-thaw cycles and the temperature increment of surrounding boundary are severely affect the stability of the slope. And the research can be a significance reference for further understanding the slope stability under freeze-thaw cycles.