St Petersburg's re-construction

On November 27th 2003, the international JV of Impregilo (Italy) and NCC (Sweden) successfully finished re-excavation of the second 800m long tube of Line 1 of the St. Petersburg Metro, Russia. The breakthrough of the 7.4m diameter Voest Alpine Polyshield TBM sees construction completed on one of the most technologically demanding sections of soft ground, segmentally lined twin tube metro tunnel ever undertaken.

The 800m long twin-tube section of Line 1 between Ploshchad Station and Lesnaya Station was originally opened in 1970 but persistent inflows of water and soil lead to the section's closure in 1995. To prevent a total collapse of the lining and further surface settlement the section was plugged with concrete bulkheads, filled with water and abandoned. To the consternation of some half million daily commuters, this has lead to a walk or bus replacement service on the journey from the city's north into the centre.

The US$178.5M re-construction contract was awarded to the JV in 1998, but economic uncertainties in the region delayed construction, and the TBM wasn't set off towards Muzhestva Station, from a launch shaft near Lesnaya Station, until early 2002.

The tunnels are situated at an average depth of 60m and cross the buried paleo-valley of the Neva River, filled with fine soils (glacial, fluvial, moraine) with inclusions of pebbles and boulders. With the groundwater level situated some 50m above the tunnel crown, contractors have battled 5-6 bar of pressure. The TBM has erected a segmental lining of five segments and a key in each 1.4m long x 350mm thick ring and modified grouting operations have been necessary to cope with the unique conditions. Special teams of trained divers have been used to carry out any maintenance of the cutterhead during downtime – under 4.8-5 bar pressure!

After slow but steady progress of around 5-6m per day, the first tube broke through in May 2003. The machine was then turned and set off back to the launch shaft at the end of August 2003. Following the breakthrough on the second tube in November 2003, the TBM is now being dismantled and the tunnels fitted out.

A trial run through the tunnels is expected in May 2004 with the line scheduled to re-open to the public in June 2004. The project has been undertaken for the Transport Committee of St Petersburg Administration with Italian consultant Geodata providing tunnel design to Russian standards and supplying technical assistance to the contractor during construction.