This article explores how geomechanical classifications influence modelling outputs in underground excavation assessments. Through 3D modelling, this study examines stability variations during different design phases and their relationship to geological data. In the early stages, geomechanical classifications based on borehole data and continuous 3D models revealed unstable scenarios affecting costs and project efficiency. As geological studies progressed, models based in discontinuous approaches provided a more feasible scenario for tunnel and pillar behaviour. This paper presents the results and comparisons of these models, aiming to quantitatively determine the differences and the technical basis, that supports the discontinuous evaluation.