Ulriken TBM in turn for home stretch 22 Jun 2017

With the majority of boring completed, the first TBM-driven rail tunnel in Norway has less than 1km to go on the home stretch towards the city of Bergen. The news was explained to TunnelTalk during a visit to the project site last week as the city hosted the successful WTC 2017 conference.

TBM is well into its hard rock drive

Best progress rates achieved by crews of the Skanska Norge-Strabag JV crews and the 9.33m diameter hard rock Herrenknecht gripper TBM have included 37.5m on the best day and 168.7m in the best week and a weekly average of 138m in February, during calendar weeks seven to 11. Best monthly progress was 671.5m, said JV Project Manager Torbjørn Bakketun.

In mid-2016 and still early in the 6.9km long TBM drive the hard banded gneiss rock, geological conditions were found to be slightly tougher than expected. There were some weak zones, which slowed production, but further into the drive the machine met harder rock with lower mica content.

Nevertheless, during the early days and through the learning curve, planned stops and geological variability, the scheduled production rate of approximately 100m/week was better with advances of more than 110m in calendar weeks and a best week of 151m. The figures were beaten as the TBM advanced, and, as anticipated, the boring operation was approaching its late stages at the time of the WTC 2017 gathering, hosted by the Norwegian Tunnelling Society NFF (Norsk Forening for Fjellsprengningsteknikk), and the planned conference site visits.

Concrete slabs placed for rail tunnel track bed

Spoil removal from the mostly unlined tunnel is by conveyor out of the tunnel. Trucks are loaded for journeys of 4km-8km to different disposal sites.

The 7.7km long tunnel is being developed by the national rail authority Bane Nor (formerly Jernbaneverket) to eliminate a bottleneck in the rail capacity through the mountainous region into the coastal city Bergen. About 800m of the tunnel was developed by drill+blast, allowing the TBM to be walked-in and get underway in early 2016, to drive from Årna to Fløen near Bergen. As the TBM advances, concrete invert elements are being placed as the operating track foundation.

The rail upgrade project also involves later refurbishment of the existing and parrallel 53-year old tunnel, which will be linked to the new tunnel by 16 cross passages and cross-over tunnels, explained Katrine Erstad, Project Manager for Bane Nor. Future works also include building a new, twin-track bridge from the tunnel portals to replace the existing single-track bridge.

Video of spoil conveyor on TBM

Project leaders: Torbjørn Bakketun, Skanska/Strabag JV (left) and Katrine Erstad, Bane Nor (right)

Drill+blast adits were also excavated near Fløen for both the new tunnel and future rehabilitation work of the existing tunnel, said Erstad. As the TBM nears the end of its drive, the breakthrough space at Fløen is tight being adjacent to the existing tunnel and in a built-up area.

During the site visit, Erstad also highlighted future rail tunnel work in the Bergen area and programmed for the 2020s as part of the E16/Vossebanen combined project with the Norwegian roads authority Statens Vegvesen (NPRA). The rail element of the scheme, running inland from Årna along a steep valley, includes two tunnels of about 18.7km and 8km. “It is a big project,” said Erstad with significant road tunnels also included along the corridor of the joint project.