ABSTRACT
Line 4 is a new, under construction, line of the Athens Metro. The bedrock of Athens is the Athens Schist, a slightly metamorphosed, intensely deformed, heterogeneous meta-sedimentary succession. The complexity of the ground conditions imposed significant challenges when these needed to be quantified for the realization of the Baseline Statements in the framework of the Geotechnical Baseline Report (GBR) that was prepared for the first time by ATTIKO METRO S.A. in 2018. No data in literature or case studies were found regarding such engineering geological conditions and GBR. Common tunnelling concepts such as mixed ground conditions had to be defined in a quantitative manner. An innovative approach was implemented that included (a) qualitative/semi-quantitative description of typical engineering geological behaviour with respect to TBM tunnelling, (b) quantification and definition of what constitutes mixed ground conditions and (c) dimensioning of karstic voids with respect to introduced sectors at the TBM excavation profile.
