Twin TBMs from Herrenknecht achieved an historic double breakthrough after boring through some of the hardest rock in the world near the city centre of Oslo while working on the Follo Line Project.

About 25,000 viewers worldwide watched the simultaneous breakthrough on September 11, 2018. Client Bane NOR and the Acciona-Ghella contracting JV are using four Herrenknecht TBMs and in the course of the project, approximately 4,250 cutter changes will be needed on each machine as they excavate the hard granite rock of Norway. “I have never had to deal with such hard rock before. You can only handle that with teamwork,” said Francesco Giampietro, long-time TBM Manager with Ghella.

The project, which is expected to finish in 2021, marked an advance of mechanised tunnelling technology in a country where conventional tunnelling traditionally dominates. Anne Kathrine Kalager, Project Manager at Bane NOR, is certain that " in the future, TBMs will be a realistic alternative in large projects, even in our extreme hard rock.” Since late 2016 the TBMs, with diameters of 9.9m each, have been boring their way through tough gneiss over a total length of around 36km. Tunnel boring represents the majority of the long twin tube tunnel at some 18.5km of a total 20km tunnel on the 22km of new rail line intrastructure.

Four TBMs are employed on the 20km Follo Line railway

Before the final breakthrough of the last two of the four machines, a total of four million cubic metres of rock has to make way. To master the mission, double shield TBMs are being used. These combine the functional principles of gripper and single shield TBMs in one machine. In stable geologies, combining these methods permits the installation of concrete segments simultaneously with boring advance.

The best performance of the TBMs under these extreme conditions is 19 rings or about 34m/day. But not only was the drive faster than expected, factory acceptance of the first TBM took place in March 2016, 11 months after confirming the order. There were 19 months between contract signing and the beginning of work of the fourth and last of the machines in Oslo in November 2016. Up to 30 Herrenknecht service experts were on site to assemble the machines.

TBMs bored through hard granite bedrock

"Teamwork makes it possible", Francesco Giampietro, Ghella TBM Manager

“We were four months ahead of the official schedule with the TBM launch,” said Fernando Vara, Project Director of the Acciona Ghella JV. During the drive, up to 40 refurbishment experts took care of the professional reprocessing of the disc cutters.

The linchpin of the drive is of the quality as the cutting tools. The disc cutters which are made of special steel, 19in in diameter and each weighing up to 372kg, are pressed against the extremely abrasive rock with up to 32 tonne of pressure on 70 circular tracks. The geological conditions result in high wear requiring a high number of cutter changes.

Expected to finish in 2021 the Follo Line Project is currently the largest infrastructure undertaking in Norway. The high-speed line will connect Oslo with Ski to the south. Before trains can travel, the two other machines must continue boring through extremely hard rock. The final breakthrough of these two TBMs heading towards Ski is expected in Spring 2019. Until then, the TBMs are boring their way through some of the hardest rock types in the world, with rock strengths of up to 300 MPa.

In a rare event, two double-shielded TBMs achieved simultaneous breakthroughs to complete their 9km drives through hard granite rock for the twin tube Follo Line railway project in Norway. In a live broadcast on 11 September, TunnelTalk readers tuned in from around the world to join the celebrations as the machines advanced their last meters and emerged into a mountain hall cavern close to Oslo city center.

Twin TBMs achieve simultaneous breakthrough

The two TBMs are twins of four Herrenknecht machines working on the project for the construction JV of Acciona/Ghella which is advancing the twin tubes of the 20km long bored TBM tunnel section of the project for Bane Nor from a central adit and working job site. The two TBMs progressing southwards in the opposite direction launched after the first two northbound machines and are expected to complete their 9km long drives in September next year (2019).

With TBM advance through the exceptionally hard Norwegian granite, rings of a one-pass precast segmental lining are erected.

The new twin-tube high-speed railway line between Norway’s capital city Oslo and the regional city of Ski, will increase capacity and reduce current travel time by 50%. It is the largest infrastructure project in Norway to date and forms an important part of the intercity rail network development by Bane NOR, the Norwegian National Railway Administration.

Great celebrations for the twin TBM crews after racing to their simultaneous breakthroughs

TBM excavation with installation of the gasketed watertight segmental lining as they progress, provides major environmental benefits with conveyor belts transporting the excavated material from the tunnels to be reused as part of the construction foundations for a new residential area surrounding the central working site.

From the breakthrough cavern of the north-bound TBM drives, complex drill+blast excavation takes the underground line through the Ekeberg Hill and into underground platforms at Oslo’s central railway station. At the south end, the TBM drives with terminate at a portal ramp where the rail lines will surface for the approach to a new station at Ski.

The breakthrough on Tuesday (11 September 2018) is a significant achievement for the tunnelling industry in Norway and will influence design and construction of several new rail lines that also require long distance tunnels through the mountains of Norway.

Two TBMs are racing towards breakthrough in Norway. The machines are a pair of the four TBMs working on the twin tube Follo Line railway project, which are now within meters of an underground breakthrough cavern close to Oslo city center. The TBMs are racing side by side in parallel drives towards breakthrough celebrations on Tuesday of next week, 11 September, starting at 11am Norwegian time.

Which of the two hard rock TBM Queens will be the first to breakthrough? They broke through at the same time!

The machines will breakthrough into a cavern in the mountain near Oslo to end their 9km long northward drives. Two TBMs progressing southwards in the opposite direction from the mid-point working access adit will have the same length and will complete the longest rail tunnel to date in the Nordic countries.

With guests and tunnel workers ringside, the breakthrough, or twin breakthrough, next Tuesday, will be the first for the 20km long hard-rock, segmentally-lined tunnel on the new Follo Line, running from Norway’s capital to the city of Ski. The final breakthroughs for the TBMs heading southward are scheduled for Spring 2019. To this point two-thirds of the Follo Line Project is now complete.

The new double track rail line will reduce by 50% the current travel time between Oslo and Ski. It is the largest infrastructure project in Norway to date and forms an important part of the intercity rail network development by Bane NOR, the Norwegian National Railway Administration.

The two TBMs working towards Oslo are racing towards breakthrough

Bane NOR chose TBM excavation with installation of a precast concrete segmental lining for the main 20km long tunnel on the project and construction consortium JV Acciona Ghella selected four 9.96m diameter TBMs manufactured by Herrenknecht in Germany for the task. Operation of the four 9.96m diameter TBMs is managed from the one centrally located job site with each pair of TBMs progressing in opposite directions towards the tunnel portals. Excavation started in early September 2016 with launch of the two northward TBMs, which are now competing to reach their breakthrough close to Oslo‘s Central Station and ahead of schedule.

TBM excavation with installation of the gasketed watertight segmental lining as they progress provides major environmental benefits compared to drill+blast excavation from several access points. Conveyor belts transporting the excavated material from the tunnels to be reused as part of the construction foundations for a new residential area surrounding the site, results in a reduced number of vehicles and traffic movements on public roads and an associated reduction in pollution. The mechanized excavation method and its precast concrete lining offers a model for future railway projects in Norway.

Factory acceptance of the last of the four TBMs at the Herrenknecht factory in Germany

The four TBMs are working through extremely hard rock formed by several glacial periods and it is the two machines heading north towards Oslo that are heading towards their breakthroughs next week. Dubbed Queen Eufemia and Queen Ellisiv, the two machines are named after courageous women with historic links to Oslo and to the Medieval Park near the mountain hall breakthrough cavern.

Ellisiv was Queen of Norway from 1046 and was married to King Harald Hardråde. She was a Russian princess. Harald forced his nephew, King Magnus, to divide the kingdom between them, and when Magnus died shortly after, Harald became sole king of Norway and Denmark. Eufemia was Queen of Norway from 1299 and married King Håkon Magnusson in St Mary's Church in Oslo. The ruins of St Mary's can be seen today in the Medieval Park, beneath which the new Follo Line railway will run in a covered subsurvace superstructure.

The race has been on between the two hard rock TBM queens for two years since their launch in September 2016 and on Tuesday next week, the winner will be revealed when the first breakthrough is recorded.