The unique tunnel boring machine "Sofia" was officially set into operation at a ceremony attended by the Prime Minister of the Republic of Bulgaria Boyko Borissov, Minister of Transport, Information Technologies and Communications Aleksandar Tsvetkov and Sofia Mayor Yordanka Fandakova. The machine was manufactured in Germany especially for the Sofia underground extension project, financed by the European Regional Development Fund through OP Transport 2007-2013. The Prime Minister stressed that this is a project that may set an example for management to the other EU-financed projects. Sofia Mayor Yordanka Fandakova named the machine after Sofia City and it will be used in other future projects by the contractor-company, Dogus Insaat ve Ticaret A.S.

The automated tunnel boring machine (TBM) ensures the safest technology for tunnel excavation in the world. Parallel to this, it reduces traffic impediments. "Sofia" TBM is of the type of mechanized shield with counter-pressure and is specially designed for soft soils with high water content as the ones in Sofia.

After its acceptance at the plant of the Herrennknecht company, Sate of Baden-Wurttemberg, the machine was disassembled and transported by road and water, i.e. by trucks and river ships (the heavier parts weigh up to 130 tonnes). The transportation took two months. The first components arrived in Sofia in January 2010 and the last - in February 2010.

TBM was then assembled again at the site of the starting shaft by the Nadezhda overhead crossing, as the process took 2.5 months. The excavation of the tunnel from separate position I of the project, Nadezhda overhead crossing - Patriarch Evtimii Blvd. will last 15 months and will be completed by the end of July 2011.

The external diameter of the tunnel will be 9.4 m, which allows placing both tracks in it. The section, where the two-way tunnel will be located, beneath Marie Louisse Blvd. and Vitosha Blvd., is 3.8 km long. The average depth will be 15 m (minimum 9 m and maximum 23 m). Nine meters will be excavated per day on the average.

TBM is 85 m long and weighs 1,600 MT.

The machine costs 15 million EUR and has been purchased by the contractor of separate position I - Dogus Insaat ve Ticaret A.S.

The tunnel construction will be carried out by 35 workers per shift - 25 in the tunnel and 10 at the starting shaft. They will work continuously, on 3 shifts, 24 hours a day, 7 days a week as everyday life in the capital would not be disturbed.