This chapter presents a comprehensive field investigation and numerical analysis of the HM perturbations induced by excavation during the connecting gallery construction within the CLIPEX project. The formation of an excavation damaged zone (EDZ) and a hydraulic disturbed zone (HdZ) significantly influences the host rock’s long-term behavior in geological repositories. Through in-situ measurements of pore water pressure and displacements, along with coupled HM numerical simulations using parameters from experimental studies, this work quantitatively evaluates the evolution of EDZ under realistic excavation conditions. The comparison between field monitoring data and numerical results demonstrates the model’s capability to capture the key HM responses, including pore pressure recovery and displacement development. The results provide essential data for understanding HM-coupled processes in clay formations under excavation conditions, supporting the design and safety evaluation of geological repositories.