Bulgaria Metro receives TBM

A Herrenknecht TBM arrived in Sofia last month ready to start work on the city’s second Metro line. From April 2010, it will carve 3.8km of tunnel that will run beneath the historical Bulgarian city as part of a project overseen by contractor Dogus Insaat ve Ticaret A.S for Metropolitan EAD.

In parts, the minimum overburden is only 3m, meaning that as the 1,2500t EPBM worms its way under railway tracks, a historical church and a built-up area, special care must be taken to ensure that the bore is undertaken sensitively and without subsidence and heave. To meet these delicate requirements, Herrenknecht has adapted an EPB Shield to meet the geological conditions (silt, gravel, sand and clay) and extreme inner city constraints.

The 84m long EPBM has a maximum torque of 24,997kNm and a total thrust of 90,883kN. Its 9.36m shield holds eight double discs, 16 bucket lips, 13 rippers, 170 scrapers, one centre tip, one over cutter disc and one over cutter ripper. Its ring length is 1.5m.

Some of the larger parts of the machine will be transported via the Rhine, the Rhine-Main-Danube-Channel and the Danube, whilst the transport of the other segments will be managed by land. 

Upon completion, the 17km long route will run from the terminus Obelya via Nadejda station, the Central Railway Station and the National Palace of Culture up to the Hladilnika district. The 8.43m diameter tunnel will run through a partial section of the line from Nadejda Junction to Sveta Nedelia Square.