The Finnish Road Administration has invited tenders for the design and planning of the US$169M Vuosaari harbour tunnels in Helsinki. In total, three tunnels will be constructed, one highway tunnel and two railway tunnels.
Firstly the US$28.9M, 1.6km long Porvarinlahti twin tube highway tunnel with a cross section of 11.9m wide x 9m high. Secondly the 620m long single bore Labbacka railway tunnel, and finaly the 13.5km long Savio single bore railway tunnel. Both rail tunnels will feature a finished cross section of 6.6m wide x 9m high and combined will cost an estimated US$75.5M.
The quality of the rock along the tunnel alignments is generally good with relatively few fractures. Only minor short sections are characterised by worse rock quality, the length of these sections ranging from 10m to 100m. There is one major 250m long weak zone along the alignment of the Savio railway tunnel, with poor or very poor rock, although this may be longer depending on the final alignment option chosen. The rock type is granite or gneiss.
The excavation method will most likely be drill and blast. Other techniques are very seldom used or even considered in Finland due to the country’s geology.
Support will mostly consist of rockbolts with reinforced shotcrete used both for support and lining. In addition, drains will be installed to arrange proper water egress. An essential part of the construction conditions is that no permanent groundwater lowering will be tolerated.
Grouting; especially pre-grouting, will be needed for long sections to control the seepage of the groundwater into the tunnels. A thermal and moisture insulation with shotcrete lining will be provided for the whole highway tunnel. In the rail tunnels, sections close to the tunnel openings will be also insulated. Construction should start in 2004 and be completed in 2008.
The project will be co-financed by the Finnish state through the Ministry of Transport and Communications and the Port of Helsinki. No final decision has been made about the exact share of both financiers. The feasibility studies and the preliminary engineering have been carried out by a consortium of Sito Group, JP Transplan, and LT Counsultants. The preliminary engineering study was completed in April 2001.
