In the last few decades a rapid development in almost all stages of geotechnical design for tunnels can be discerned. Analysis and computational methods are fields in which significant progress has been made. Nevertheless, regardless of the capabilities offered by the numerical tools, the results can still involve uncertainties when parameters are used directly without considering the actual failure mechanism of the rock mass in tunnelling. This work analyzes the procedure that treats tunnel behaviour type as fundamental information for the excavation and support measures. The research is based on the analysis of design and construction data from 62 non-urban tunnels of the Egnatia Highway in Northern Greece. Within this framework, one classification scheme and one detailed characterization scheme for assessing the rock mass behaviour in tunnelling are presented. The understanding of the failure mechanism enables the selection of the appropriate design parameters and the definition of the support philosophy. Support principles for every behaviour type are proposed.