Hard rock challenge for Norway’s largest TBM 20 Oct 2016

The largest TBM ever procured for a Norwegian tunnel project is delivering solid progress to bring hard rock tunnelling to almost 50% completion on the New Ulriken project near Bergen – host city for WTC 2017 in June next year.

2.7km of the New Ulriken Tunnel is now completed

Following contract award in May 2014, the JV contractor of Skanska Norge and Strabag is driving a 9.33m diameter Herrenknecht hard rock gripper TBM through a predominant geology of gneiss. Final breakthrough is expected soon after WTC delegates get the opportunity to visit the landmark project as part of the site visit program of WTC2017.

Hans-Egil Larsen, Head Project Manager for the client, the national rail administration Jernbaneverket, told TunnelTalk that tunnelling on the NOK1.3 billion (US$220 million) underground excavation contract is progressing well and that the contractor JV is meeting all challenges presented thus far.

The New Ulriken project will see the addition of a 7.8km long parallel rail tunnel to the existing 52-year old tube that takes the line into Bergen. Jernbaneverket, supported by its design team of Norconsult and Basler & Hofmann, is making the major investment to boost capacity and improve both safety and network access into the important port city on the country’s west coast.

Two weeks ago, Jernbaneverket launched the last main phase of procurement for the New Ulriken project, briefing interested contractors on the M&E, track, signalling, station upgrade and surface works packages needed to complete construction of the new tunnel and also to refurbish the existing tube. Jernbaneverket puts the estimated total cost of the additional works at US$180 million, with tender documents for many of the packages due to be issued in Q1-2017.

New Ulriken parallel tunnel alignment

The new alignment was originally planned as drill+blast, but in 2012 the rail authority decided it would consider contractor proposals for what would be its first-ever use of TBM excavation. At the same time it was also considering the possibility of using TBM technology for another of the country’s largest underground projects – the high-speed Follo Line between Oslo and Ski – on which the first of four Herrenknecht TBMs launched last month (September).

The new rail tunnel is approximately 7,800m long, and runs from near Fløen to just short of Årna. It will be linked to the existing tunnel by 16 cross passages and cross-over tunnels. Geology along the majority of the bored section of the tunnel is through a mixture of granitic and banded gneiss – with 800m of drill+blast excavation required in addition to the 7,000m of TBM tunnelling.

The contractor JV turned to Herrenknecht to supply a 5,600kW machine capable of delivering a total thrust force of 27MN and a torque of 10MNn (breakout is 16MNn). The cutterhead is equipped with 62 x 19in discs, and can achieve a rotation speed of up to 6.4rpm. The mechanised tunnel system is set up for probe drilling, injection, bolting and shotcrete application, with the lining of the bored hard rock tunnel formed by PE-foam boards and a slab track system.

To execute the main tunnel contract the contractor JV elected to launch from the opposite side of the mountain, heading back towards Bergen from the narrow valley on the Årna Station side. In the Årna valley, the JV contractor has completed extensive drill+blast, as well as surface drilling works, to cut into the hillsides and construct the new concrete portal structure. The assembly area for the TBM sits between the portal and the station.

Drill+blast works make up 800m of the 7,800m alignment

After being shipped in pieces to Bergen harbour and transported to site by road, machine assembly began in the third quarter of last year (2015). By November the TBM had been stepped through the portal and along the section of tunnel that had been opened by drill+blast, and beyond the crossover tunnel zone, ahead of machine launch in the early part of this year (2016).

By the end of February the TBM had advanced approximately 200m. From April the TBM moved ahead of the general average schedule rate, and by the end of May had advanced a total of 1,200m through granitic gneiss.

In early June, Larsen, along with the JV contractor’s Head Project Manager, Torbjørn Bakketun gave an update on progress at the TBM Applications Conference.

Early performance data reported 50m/week advance rates from February, ramping up to 80m/week from early April. From this point the scheduled production rate is approximately 100m/week, but shortly before the conference the TBM had already achieved a number of weekly advances of more than 110m, and a best of 151m.

Briefing TunnelTalk in August with a further update on progress, Larsen said the TBM had been progressing ahead of schedule but that progress had been slowed as a result of encountering harder rock, which had been expected during the first 3,000m of the alignment. The production rate achieved since June had been approximately 80m/week, he said.

Assembly of the 9.33m gripper TBM in late 2015

This was primarily due to harder rock with a lower mica content, explained Larsen, but other factors such as planned maintenance and the summer vacation period contributed. Overall excavation progress, however, remains ahead of schedule, and by the end of September the Skanska/Strabag JV had advanced the TBM through almost 2,700m.

Progress has also been slowed as a result of a number of encounters with weak zones, but the expectation is that progress will be rise once the machine passes out of the granitic and into the banded gneiss that constitutes most of the remainder of the TBM drive.

TBM breakthrough is tentatively predicted in August 2017, said Larsen, who added that all main drill+blast work on the project is finished but that work on the cross passages has yet to start.

Upgrade works to the existing rail tunnel, which was opened in 1964, are scheduled for 2021-22 as one of the final tasks in the overall scheme.

The existing tunnel has cross sections of 25m²-30m², and is 7.8km long with patches of uncovered PE-foam as water and frost proofing. The scope of the works also includes breakthrough for two pre-excavation crossover tunnels linking to the new rail tube near the Årna end, and breakthrough for an access tunnel at the Fløen end.

As with all other completion works on the project, the final scheduling of the upgrade works on the existing rail tunnel depends on parliamentary decision, said the client.