Coupled thermo-hydro-mechanical anisotropy characteristics of clay-based on the ATLAS III in situ heating test

Boom clay, as a study case for the potential geological disposal of high-level and long-lived radioactive waste in Belgium, can be considered as a transversely isotropic geomaterial. This paper presents a coupled thermo-hydro-mechanical (THM) elasto-plastic damage model which is based on the Drucker-Prager cap model. The model is able to reflect thermal effect on the strength, elastic modulus and permeability of Boom clay. The developed model was implemented in ABAQUS finite element code through subroutine USDFLD. Three dimensional numerical simulation analysis was conducted of the ATLAS III in-situ heating tests at the HADES underground research facility to validate the proposed constitutive model. The results of the numerical simulation are compared with in situ measurements in which the coupled THM properties of Boom clay were analyzed. It indicates that the model can reasonably depict the main features of coupled THM anisotropy behaviors of temperature and pore water pressure. Remarkably anisotropic characteristics were found on temperature and pore water pressure changes of Boom clay with thermal load. The pore pressure in the horizontal plan shows temporary decrease and then increase after increasing power, and temporary increase and then decrease after decreasing power. The pore pressure in the vertical plan shows immediate increase after increasing power and immediate decrease after decreasing power. This study shows that the anisotropic coupled THM elasto-plastic damage model can accurately reproduce the temperature and pore water pressure changes during the heating test. The results of this study can provide valuable information for the design and operation of similar engineering/in situ tests