ABSTRACT
Conventional tunnelling requires continuous adaptation of the excavation and support method to the actual ground conditions in order to get an economical and safe construction (Schubert et al., 2003). This observational approach requires among others the continuous collection of information on rock mass type, structure, and quality, as well as the system behaviour. Very important in this context are geometric properties of the rock mass and especially the discontinuity network as observed at every tunnel face and subsequently descriptive parameters which altogether supports to establish a plausible rock mass model.
