The Follo Line Project in Oslo is a revolution for tunnel-rich Norway. Previously, tunnels have mostly been built the traditional way with explosives. For the largest infrastructure project in the land of the fjords, tunnel boring machines have been used. Four large Double Shield TBMs (Ø 9,900 mm) have each excavated approx. 9.5 kilometers of tunnel for the new railway connection from Oslo to Ski.
In Norway, tunnels have previously been driven with explosives. Now we know that TBMs are an alternative, even in our extremely hard rock.
Anne Kathrine Kalager, Project Manager, Norway’s state railway company Bane NOR
Norway breaks new ground
Previously, tunnels in Norway have mostly been built with the traditional drill & blast method. Only in a few hydropower projects smaller tunnel boring machines were used. The best way to deal with the indigenous rock is by means of explosives, because tunnel boring machines would have a tough time with it – for a long time that was the prevailing opinion. The Follo Line Project brings movement into this tradition.
Using mechanized tunnelling technology, the unique large-scale project is creating the longest railway tunnel in Norway and eliminating a bottleneck in the transport network of the future. The new twin tube runs 20 kilometers from the municipality of Ski to the south of Oslo right into the center of the metropolis. With the new build on the route, travel time by rail will be shortened by about half.
Decisive advantages of the TBM solution
Tunnel boring machines provided decisive advantages in this project. To carry out the project as quickly as with mechanized tunnelling, for drill & blast a total of seven jobsites would have been needed in the metropolitan area, some of them difficult to access. Drill & blast tunnelling would have meant a huge burden on the traffic and the many residents living near the jobsites. In contrast, the TBM solution gets by with only one central point of attack. Two 900 meter long access tunnels connect the large Åsland jobsite on the surface with two underground caverns. From there, two machines each bored south and north respectively to create the two tunnel tubes. The caverns initially served as the assembly site for the four TBMs and were then used as logistical nodes for the drive.
High-tech tunnel boring machines for a fast advance
Double Shield TBMs are among the most technically sophisticated tunnel boring machines. They combine the functional principles of Gripper and Single Shield TBMs in one machine. In stable geological conditions, combining these methods permits the installation of concrete segments parallel to the drive, resulting in very high performance rates. The powerful technology is thus ideal for driving long tunnels in hard rock. For the Norwegian gneiss with up to 300 MPa Herrenknecht equipped the four big machines with 265 tonne, especially hardwearing cutterheads and 13 engines per TBM with 475 PS each.
I’ve never had to deal with such hard rock before. You can only handle that with teamwork.
Francesco Giampietro, TBM Manager Ghella
Less than a year after signing the contract, in March 2016 Herrenknecht presented the first machine of the Double Shield quartet to the customer for factory acceptance in Schwanau. There were only 19 months between the signing of the contract and the fourth and last machine beginning operations in Oslo.
The jobsite team assembled the machines in Norway in gigantic caverns that had been excavated by the construction companies. The starting shot for the first machine was given in early September 2016 in the presence of the Norwegian Prime Minister Erna Solberg and the Minister of Transport Ketil Solvik-Olsen. The fourth Double Shield took up its employment in November 2016 – four months ahead of schedule. That means that with the extensive support from the Herrenknecht team four large-diameter machines were installed on the jobsite ready to excavate in only 6 months.
On average, seven Herrenknecht specialists were on site every day to assist the TBM manager and his people with incidental maintenance and repairs, but also to support the advance. Up to 50 refurbishment experts at the Herrenknecht headquarters worked on the professional rebuilding of the disc cutters. The advance stands and falls with the quality of the excavation tools. The cutter discs are pressed against the extremely abrasive rock with up to 32 tonnes of pressure on 70 concentric tracks. During the entire project, about 3,000 disc cutters had to be changed on each machine.
The outstanding performance and teamwork of the excavation crews and Herrenknecht manifested in best performances of over 158 meters per week and up to 36 meters per day.
On September 11, 2018 the first two Herrenknecht TBMs reached their final goal after about 2 years of tunnelling through tough Norwegian gneiss. Via live stream around 25,000 viewers around the world watched the almost simultaneous breakthroughs of the two Herrenknecht sister machines "Queen Eufemia" and "Queen Ellisiv" in Oslo. The final double breakthrough of the two TBMs "Anna" and "Magda" on February 26, 2019 in the Norwegian city of Ski marked the finish line for tunnelling of the two approximately 20 kilometer long tunnel tubes for the railway project Follo Line. Tunnelling for the biggest infrastructure project of the country was thus finished.
After the planned commissioning of the railway line in late 2021 express trains will be driving through the two new tubes at up to 250 kilometers per hour. Travel time between Oslo and Ski 20 kilometer further to the south will shorten from 22 to 11 minutes. For the Norwegian capital with its 600,000 inhabitants and the region around Ski, which expects population growth of 30 percent by 2025, the Follo Line is a lifeline of the future.
|Column 0||Column 1|
|Tunnelling Length||37,270 m|
|Contractor||AG JV (Acciona-Ghella Joint Venture)
4x Double Shield TBM:
Diameter: 9,900 mm
Lining method: Segmental lining
Cutterhead power: 4,550 kW
Torque: 11,115 kNm