Speaker: Yifan Xu

Date: Thursday 13th of February 2025, 1:15pm.

Abstract:

Variational gradient damage modeling, known nowadays as the variational phase field method, has been widely utilized in recent decades thanks to their efficiency in describing the transition from damage to fracture and predicting fracture nucleation and growth. In this work, we aim at proposing a phase field based Cohesive Zone Model (CZM) to simultaneously investigate the full coupling between gradient damage, poroelasticity and fluid flow phenomena in saturated porous media, as well as to well describe the damage zone that develops near the tip of quasi-brittle fractures. To this end, we mainly rely on the recent works of Zhang et al., 2024 (J. Mech. Phys. Solids, 187, 105614) and Wu, 2017 (J. Mech. Phys. Solids, 103, 72-99) in order to incorporate the cohesive zone effect in the corresponding incremental variational formulation of this fully coupled system. The proposed incremental variational approach consists in the minimization of a three-field incremental energy functional, which depends on the displacement and damage fields of the skeleton phase of the porous media as well as the pore fluid pressure. For numerical implementation, we adopt a semi-staggered optimization algorithm by making use of FEniCS platform and apply it to simulations of the KGD fracture problem and hydraulic fracturing problems involving multiple cracks for which corresponding analytical solution and/or numerical results are available. Taking advantage of this framework, this is finally applied to assess the feasibility and stability of an industrial radioactive waste repository in the Callovo-Oxfordian (COx) claystone formation, where the host rock presents significant cohesive characteristics. The numerical results are compared with the in-situ observations. Reliable predictions such as the extension of the excavation-induced damaged zone (EDZ) as well as pore pressure distribution are provided.