A Multiscale Numerical Method for Studying Resaturation Phenomena in the COx Claystone Damaged Zone

Abstract

In the context of the planned deep geological disposal of nuclear waste in the Callovo‐Oxfordian claystone (COx) in France, this research focuses on the long‐term behavior of the host rock damaged during tunnel excavation. A general multiscale numerical methodology is developed and applied as a first step toward analyzing the hydro‐mechanical response of a representative damaged zone surrounding the excavated drifts during resaturation, while accounting for swelling phenomena. A nonlinear viscoelastic‐viscoplastic numerical model incorporating irreversible creep mechanisms is employed to describe the clayey rock at the material scale. The evaluation of the damaged matrix behavior is conducted using 3D representative elementary volumes (REVs) of the fractured host rock, consisting of the clay matrix containing dispersed penny‐shaped cracks. A multiscale numerical technique based on a modified Finite Element squared (FE2) method is then used to simulate the response of a macroscopic gallery region, which is discretized into zones sharing similar crack density parameters estimated from experimental data. This approach is intended to provide a first‐order assessment of the damaged zone response, and constitutes an initial contribution toward a more comprehensive multiscale modeling framework.