At the preliminary stage of a project, rock mass classification are cheap tools which ensure a rapid determination of the support requirements in a tunnel or in a gallery. These empirical classification come from a limited number of excavation cases and that's why they should be used with a lot of caution. In order to test the relevance of the Bieniawski and Barton classification and of the AFTES recommendations, EDF chose to apply them on existing sites.
Au stade des etudes preliminaires, les classifications de massif rocheux sont des outils economiqees qui permettent une determination rapide du soutenement à mettre en place dans un tunnel ou une galerie. Ces classifications empiriques sont issues d'un nombre limite de cas d' excavations et doivent donc être utilisees avec beaucoup de precautions: Afin de tester la pertinence des classifications de Barton et de Bieniawski, ainsi que celle des recommandations de l' AFTES, EDF a choisi de les appliquer sur des sites deJà existants.
Am Anfang eines Projektes sind die Klassifierungen von Felsmassiven wirtscraftliche Werkzeuge, die eine schnelle Bestimmung von der nötigen Aufstuetzung eines Tunnels oder einer Galerie ermöglichen. Diese empirischen Bestimmungen stammen aus einer geringen zahl von Aushöhlungsereignissen und deswegen sollen vorsichtig benuetzen warden. Um die, Triftigkeit der Barton's und Bieniawski's Klassifierungen, sowie der AFTES's Empfehlungen zu pruefen, wahlt EDF sie auf bestehende Anlage zu verwenden.
During the preliminary stage of an underground excavation project the use of the rock mass classifications can be of considerable benefit to estimate the support requirement. Nowadays, we use the classification of Bieniawski (Rock Mass Rating) or/and the tunneling Quality Index (Q) of Barton. Both are a multi-parameter classification which gives a value of the rock mass quality, by combining the rating assigned to the different parameters., The French method named the AFTES recommendations is not a classification since it refuses to combine all the parameters, Even if the classifications ensure that all the relevant information has been considered, they should be Used with considerable caution. In order to have an appreciation of the use, applicability and limitation of each classification, EDF decided to test these methods on different kinds of rock mass (sandstone and shale).
EDF chose to assess the rock mass rating (RMR system), the rock mass quality Q and the recommendations of the AFTES in the hydroelectric sites of Super-Bissorte (Maurienne) and Revin (Ardennes). The first one is excavated in sandstone at a depth of 230 m below surface. The second one is excavated in shale which is, characterized. by the high density of the schistosity plans (spacing of discontinuities < 60 mm).
Because of the heterogeneity of the rock mass, each gallery is divided into a number of structural regions and each region is classified Separately. Some zone reveal problems such as the presence of unclassifiable parameters, the difficulty of the principal family choice or the notion of the boundary between family set and erratic discontinuity.
