The Løvstakken Tunnel will one day connect the Fyllingsdalen district with Kristianborg in the Årstad district. For this purpose, two parallel tunnel bores of around three kilometers length are being driven straight through the mountain: a double-track light rail tunnel for the Bybanen and a safety tunnel that will also serve as a pedestrian and cyclist passageway – soon to be the longest of its kind in Europe. 

In addition, two caverns of 200 meters in length have been excavated the west side, in Fyllingsdalen. These will be used as an underground depot and maintenance facility for Bybanen trams. The two caverns will have a direct connection to the rail tunnel. The tunnels and caverns are being created through conventional blasting, with approximately 500,000 cubic meters of excavated material to be removed in total. The project is being executed entirely by means of BIM. Both portal construction sites feature state-of-the-art water treatment facilities from Alwatec, while the use of electric machinery and vehicles as well as a mud press help to minimize CO2 emissions.

In February 2019, the first blasting operations took place in Fyllingsdalen. Extensive work was also carried out on the portal there, including a cut-and-cover tunnel of around 70 meters length, numerous retaining wall structures and traffic diversions. The installation site with the portal is in a densely populated area, with one of Bergen’s largest and most popular shopping centers located just 50 meters away. 

In mid-2019, the team unexpectedly encountered an aquiferous zone. In some places, up to 1,000 liters per minute shot out of the boreholes. As a result, the additional pre-injections required made operations that much more difficult. To minimize delays, it was decided to start driving work from the eastern side in Kristiansborg. This portal is also located in the middle of a residential and commercial area, and even lies partially under the E39 highway. Due to the difficult geology, excavation started there using 3*10 m pipe umbrellas.

The rock conditions continue to pose a major challenge for the teams. Water inflow remains a problem on both sides, with the aquiferous layers currently showing signs of coming to an end, even though this is difficult to predict and could change quickly. Systematic pre-injections are used to displace the water before driving operations, while post-injections are applied where necessary for further sealing.

The global COVID-19 pandemic has also necessitated planning adjustments, since regulations have changed several times, and because import of foreign workers in principle was stopped for some time. Through proactive testing of the teams under the supervision of a medical officer, the risks of infection and adverse effects on the construction site have been kept to a minimum.

The tunnels are currently around two thirds complete, and driving is progressing steadily on both sides. In the connecting tunnel between the caverns and the rail tunnel, Renesco has already been engaged in waterproofing the interior work since November 2020. The operations of the various Marti Group companies involved are scheduled for completion in spring 2022. 

Marti Tunnel AG
Seedorffeldstrasse 21
CH-3302 Moosseedorf
+41 31 388 75 10