The gallery excavation induced damaged zone (EDZ) is unavoidable. In the case of a geological disposal system for HLW, the change in the host rock properties in the EDZ may potentially be important with respect to the long-term evolution and the performance of that system. Predicting the extent of EDZ and the fractures’ network topology remains a challenge. This study aimed to simulate numerically the extension of this zone around the Connecting gallery (HADES URL, Mol, Belgium), in Boom clay through analyzing the evolution of strain localization in shear bands mode. To realistically model the involved phenomena, the concrete lining is considered on the gallery wall highlighting its impacts on the evolution of convergence and EDZ around the gallery. This paper focuses on analyzing the coupled hydro-mechanical behavior of Boom clay during and after excavation with respect to the evolution of localized shear bands around the gallery and the contact mechanism on the interface between the clay massive and the lining. To assess the reliability of the proposed approach, a discussion on some in-situ observations during the gallery’s construction is performed based on which a good agreement is found between the in-situ evidence and simulated results.