In open excavation sites, desiccation cracking can occur due to variations in temperature and relative air humidity. This phenomenon is particularly significant in the context of radioactive waste disposal, as cracks can impact both structural integrity and radionuclide migration. At the Mont Terri Rock Laboratory in Switzerland, situated within an Opalinus Clay formation, similar desiccation cracks have been observed in the Cyclic Deformation (CD-A) experiment. This experiment involves measurements such as water content, suction, crack propagation, and deformation, which are analyzed and interpreted using hydro-mechanical numerical models. Our approach uses a hydro-mechanical model that employs a macroscopic poromechanic methodology and incorporates the Richards assumption for partial saturation. In this study, we focus on the hydro-mechanical behavior of the open twin niche within the CD-A experiment at the Mont Terri Rock Laboratory, especially during periods of desaturation, such as the winter season, characterized by a decrease in relative air humidity (RH) and an increase of desiccation cracks. Utilizing a combination of field-acquired material parameters and data from existing literature, the proposed model assesses the unsaturated hydro-mechanical response. This includes deducing fracture parameters that are crucial for understanding the crack development process. We compare the model’s predictions and observed in-situ crack formation, paying particular attention to how these cracks correlate with changes in RH [1]. Furthermore, the study explores the impact of enhanced permeability on crack propagation, offering insights into the relationship between environmental conditions and local changes in geological formations. This comparative analysis not only enhances our understanding of crack development but also aids in predicting and mitigating potential risks associated with radioactive waste disposal.