Bohren, Sprengen, Fräsen: Können die geologischen faktoren der gebirgslösung quantifiziert werden?

Is it possible to put numbers to geological parameters concerning excavatability? Are there only rock mechanical properties which really can be quantified? Is a classification system possible for excavation by drilling and blasting or cutting, including all necessary geological and geotechnical parameters? These questions arise when the behaviour of rock mass material has to be considered during underground excavation. Determining tunnel stability is a key issue during preliminary site investigation. In contrast, problems of excavatability have been mainly ignored. While the choice of an economic tunnelling method is admitted a certain priority in the planning stage, special investigations for rock fragmentation, e.g. drilling or cutting performance, rock mass blastability or tool wear, are carried out quite rarely. This contribution explores possibilities to quantify key parameters for rock mass excavatability in drilling, blasting and cutting by TBM and roadheaders. Although rock mechanical properties play a key role, geological parameters are rarely fully included in most projects. In some cases, the influence of geological features on rock fragmentation can be much higher than varying rock properties. Geological difficulties can have a high impact on the economics of an underground construction project, especially when the chosen excavation system turns out to be unsuitable for the conditions encountered. Thus it can be argued that the geological and petrological characteristics of the rock mass should be evaluated with the same degree of effort as that for the geotechnical prognosis. Furthermore, mechanical parameters are of limited value, if the rock mass is composed of anisotropic and inhomogenious material. Inhomogeneity and anisotropy obviously play a key role during the process of rock fragmantation.