Swedish national transport authority Trafikverket is removing a serious bottleneck in the rail network through the urban heart of Gothenburg with investment in the 8km long West Link project. Three-quarters of the entire rail link and its three stations will be underground in both rock excavation and major concrete box construction. The line will increase rail capacity is vital for the west coast city of Denmark as it is a key industrial port and transport hub for Scandinavia.
The West Link project emerged from a transport strategy developed by Trafikverket in cooperation with the city and regional authorities, and is funded 50:50 from national and local funding. The estimated SEK 20 billion project (in 2009 prices), about US$2.5 billion, is anticipated to be in service by 2026.
The West Link has a 6km long section in single tube, twin-track tunnel and three new underground stations at Centralen, adjacent to Gothenburg Central terminus, Haga and Korsvagen (Fig 1).
Located beside the Gota River, the geology along the alignment has a variable rockhead, with small infilled channels and a major reach of infill and soft marine clay at the northern end (Fig 2). The bedrock is gneiss with joint sets, some foliation and zones of weakness in the rock mass. Groundwater levels adjacent to the river are high.
As a consequence, the majority of the tunnel, approximately 4km, will be excavated through rock. The remainder, in the northern part, will be built as a large concrete box structure through infill and clay over a 2km stretch (Fig 3).
The West Link is designed to take full size trains for its entire length. Dimensions of the tunnels are:
The procurement and construction strategy splits the project into five main civil engineering packages: Olskroken, Centralen, Kvarnberget, Haga and Korsvagen. Trafikverket has awarded the Olskroken and Centralen Lots to date and prequalification for the next large tunnelling lots are due in by 30 September.
The Olskroken Lot, focusing on surface works at an existing central railway node, was awarded in 2015 to a JV of Peab, WSP and Infranord. It is a two-stage design-build partnering contract involving early contractor involvement (ECI). The contract sum is to be set at the end of Stage 1 design and planning, which is expected at the end of 2017. The construction Stage 2 will end in 2023-24 and may also include further ECI, subject to agreement.
The Centralen Lot for the station and adjacent tunnels was awarded to a JV of NCC, Cowi and Thyrens in 2015. Procurement is again a design-build/ECI two stage process with the contract sum to be set at the end of Stage 1 in December 2017 and with the Stage 2 construction anticipated in 2023-24.
The deep soft clay and bedrock of the Centralen Lot is seen as among the most demanding parts of the project. For the station alone, the works involve a cut-cover-cover excavation of about 400m long x 60m wide and to a depth of about 15m.
Various preparatory works are also underway including utility re-routing along the Olskroken-Residenset corridor. The SEK 150 million (US$17.5 million) contract is being performed by NCC and is due for completion in January 2017.
Ongoing procurement activities are most immediately focused on the upcoming prequalification deadline of 30 September for the Haga and Kvarnberget civil lots located in the middle of the project. Tender documents are to be issued to prequalified parties in November for submission of proposals by April 2017.
Trafikverket Project Director Bo Larsson told TunnelTalk there will be a maximum of five prequalified parties for the main contracts. Larsson confirmed that the excavation method for much of the rock tunnel is expected to be drill+blast and added that optimisation of the tunnel design is still underway.
Key civil works involved in the Haga package involve construction of 1,520m of main tunnel with 1,220m in rock and a 300m long section of concrete box tunnel for the station, plus 1,310m of the parallel service tunnel in rock, and construction of three entrances and three ventilation shafts.
Total excavated volumes of rock and soil at the Haga Lot are expected to be about 650,000m3 and 340,000m3, respectively.
Within the one contract lot, Trafikverket has separated the rock excavation as construction-only and the concrete box works as design-build.
Works for the relatively short Kvarnberget Lot, on a bend of the tunnel alignment and running closest to the river, features complex works through rock-soil interfaces.
Deadline for prequalification to the last main civil lot on the project, the Korsvagen Lot at the southern end of the project, is 15 December. Tender documents are to be issued to prequalified parties in February 2017 for submission of proposals by October 2017.
The Korsvagen contract package includes a total length of 3,240m in main tunnel, split 2,120m in rock and 1,020m in a concrete box structure for the station, plus a 2,540m long section of the parallel service tunnel in rock and three entrances and two ventilation shafts.
The total volumes of excavated materials in the Korsvagen Lot are 761,000m3 of rock and almost 400,000m3 of soil.
Like the Haga Lot, Trafikverket has separated the procurement method of the Korsvagen Lot to construction-only for the rock excavation and design-build for the concrete box works.