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.