Final design for Helsinki tunnels

The final design phase is under way on the US$270M Vuosaari harbour tunnels project in Helsinki, Finland. Three tunnels will be built, the construction tenders for which should be invited next summer.

The project includes the 1.6km long Porvarinlahti twin-tube road tunnel, the 620m long Labbacka single-bore rail tunnel, and the 13.5km long Savio single-bore rail tunnel (see diagram).

Consultant JP Suoraplan (part of the Jaakko Pöyry Group) is carrying out the final design for the client – a group led by the Finnish Road Administration, along with the Port of Helsinki and the Finnish Rail Administration.

The rail tunnels are being built to carry freight to Vuosaari harbour. Only one train will use the tunnels at a time, because the frequency of traffic is very low – about 20 trains a day. "We are not considering a second tunnel in the future," Kari Surjonen, JP Suoraplan lead designer told T&TI.

The rail tunnels will be 6.6m wide and 9m high, and extensive studies have been carried out to ensure that the alignment will be through the most solid rock possible. Construction will be by drill and blast.

Three access tunnels connecting to the Savio rail tunnel will be used to transport the blasted rock to the harbour, where it will be used for construction. The ventilation shafts will be bored from below.

Kari Surjonen said that despite extensive geotechnical analyses, there will some very demanding sections. "There will be weakness zones, high ground water levels and pressures," he told T&TI. "We think that in the weak zones, we will need rapid reaction; we will need immediate reinforcement after each blast. And we have also recommended the use of heavy support structures during the construction."

The 1.6km long Porvarinlahti twin-tube road tunnel is bored under a lake with only 7m of overburden. Its wide profile (15m wide and 9m high) could be problematic, but Surjonen is confident: "The rock quality is quite good at this point. It will not be a very bad situation, but we will have to take it very carefully," he said.

The consultants are also discussing design aspects with local manufacturers, such as Sandvik Tamrock, to factor in the limitations of tunnelling machinery.

The Vuosaari Harbour project will help transport the one third of Finland's foreign trade that passes through Helsinki's harbours. Construction should start next year, and be completed in 2008.

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Vuosaari harbour tunnels