Picture of the construction pit for the new Losmasse tunnel in Trondheim, Norway.

Softsoil Tunnel in Trondheim

In 2013, NCC completed the construction of a tunnel project on the E6 expressway in Trondheim city center. The contract had a value of 554 MNOK.

Careful planning and good cooperation

NCC was awarded the project to construct a complicated tunnel in Trondheim city center. The project was conducted in close cooperation with the Norwegian Public Roads Administration, NCC's own advisors and the Norwegian Directorate of Public Roads applying an approach focused on successfully carrying out a project rather than solving conflicts. NCC held its own series of meeting on the theme of geotechnics to keep the focus of the project on implementation and quality.

Exciting project with challenging surroundings

NCC's contract was for a 500 m road with a 350 m concrete tunnel. The area had a high proportion of quicksand that had to be stabilized using extensive piling and lime cement stabilization methods before excavation work could begin. The concrete tunnel was built in a 20 m deep construction pit, through quicksand in a city area that included both protected buildings and high volumes of transit traffic on the road (E6 expressway), footpaths and railways. The construction pit was subject to particularly strict requirements on how rigid and watertight it was.

The obstacles of a constricted construction site, polluted soil and many phases of traffic diversions made this one of the most challenging road projects in Norway to date. The project was part of the E6 expressway Trondheim to Stjørdal, under which much of the transit traffic in Trondheim was to be routed down into tunnels beneath the city, thus improving the urban and living environment.

Intense focus on EHS

The project had an intense focus on environment, health and safety (EHS) work, since the construction pit was so constricted and many activities were taking place simultaneously. Safe work analyses and safety rounds were major focus areas of both developer and contractor.

Innovative Technology

NCC’s method proposals involve several elements not previously seen in Norway. These include:

  • Extensive use of lime cement stabilization, for example, limestone/cement cast as a “block” to ensure a sealed base for the pile pit. Lime cement mixed into the sand to obtain a soil consistency that could be excavated.
  • Drilled secant piles in the construction pit (first in the world) that provides extra rigidness and strength and significantly contributes to ensuring that water does not penetrate the border between quicksand and rock in the pile line.
  • Jet grouting as additional protection between the construction pit and the pile wall.
  • Low-heat concrete containing fly ash has been brought to a new level.

Civil engineering project of the year 2014

The softsoil tunnel was named “Civil Engineering Project of the Year 2014” and the jury’s citation was as follows: “The project serves as a prime example through its excellent organization and willingness to use new technical solutions in its implementation.”