An update of the “multiple graph” approach for the preliminary assessment of the excavation behaviour in rock tunnelling

The so-called “multiple graph” approach is a useful tool for the preliminary assessment of excavation behaviour in rock tunnelling, as well as to rationally select the pre-defined support section type at the tunnel face, during the construction phase. In a simplified but rational way the potential typical deformation phenomena (hazards) for tunnelling in rock are identified through the quantification, in a logical sequence, of fabric (1), strength (2), competency (3) and self-supporting capacity (4) of a rock mass. Based on this preliminary analysis, the tunnel design can consequently focus on the detected potential problems, implementing with the required detail the most adequate methods of analysis and calculations. In this paper, the fundamental bases of the method are summarized and some new considerations are presented.