The metro system in Sofia was to be expanded. The current Metro Line 1 was to be supplemented by an additional Line 2 in the form of a 17-kilometer section planned from the Obelya terminal via Nadejda, the central railway station and the National Art Gallery as far as the Hladilnika district. This involved underpassing railway tracks, a historic church and developed land along a 3.8-kilometer section from Nadejda Junction to Sveta Nedelia Square. At some points along the route, minimum overburden was a mere three meters. A sensitive undertaking which needed to be mastered without subsidence or elevations.
Herrenknecht supplied the EPB Shield as well as other additional equipment for a most efficient tunnelling process such as: multi-service vehicles for transporting the segments on the site, a tunnel belt conveyor system for transporting excavated material, 14 moulds for segment production as well as a guidance system for determining TBM positions and navigation during advance, including a ring sequence program.
Since the start of tunnelling, the teamwork of tunnelling specialists on site and Herrenknecht technology proved of value: more than 220 meters of new tunnel were built in one week. On August 29, 2011, the jobsite crew celebrated breakthrough after 3,770 tunnel meters.