Optimized solutions in the construction of a new cut-and-cover culvert on the Vestfold Line delivered major gains for cost and climate
Despite the presence of quick clay in the ground and the need for lime-cement stabilization, Veidekke and geotechnical consultant Norges Geotekniske Institutt significantly reduced both costs and greenhouse gas emissions for a new tunnel project on the Vestfold Line. Veidekke will carry these lessons into future projects.
By optimizing lime-cement stabilization in the excavation pit and thereby reducing the use of binder, costs and greenhouse gas emissions were reduced by 40% and 36%, respectively. ( Photo: NGI)
Press release – Tuesday, 1 July 2025
“Throughout the project, our collaboration with NGI has been very strong. We worked closely together on the geotechnical measures and jointly developed solutions that saved the project both time and money,” says Einar Helgason, Design Manager for UDK 02 Drammen–Kobbervikdalen at Veidekke.
The client, Bane NOR, commissioned the construction of an 830-metre transition from the open section at Drammen Station to the Skoger Tunnel on the Drammen–Kobbervikdalen stretch of the new Vestfold Line. This was executed through a 540-metre excavation using a cut-and-cover solution and a 290-metre soft-ground tunnel. NGI served as geotechnical consultant for the first of these two components.
The culvert itself was constructed in an excavation approximately 12 to 20 metres deep. A combination of sheet pile walls and secant pile walls was used as support structures, with internal bracing, lime-cement stabilization, and a jet grout arch beneath the excavation base.
The area features challenging ground conditions, including zones of quick clay. In addition, construction had to minimize disruption to train traffic on the existing Vestfold Line. The work therefore had to be carried out in stages, which created opportunities to test whether the work could be performed in a more cost-efficient and environmentally friendly way.
Halved lime-cement usage
One key question was whether it would be possible to optimize lime-cement stabilization in the excavation pit, where quick clay overlays moraine deposits. Lime-cement stabilization between the sheet pile walls was selected to prevent base heave.
“In total, 5,590 lime-cement columns were installed. The work was carried out in several phases to maintain traffic on the existing Vestfold Line throughout the project. This also allowed us to optimize the stabilization process,” says Per-Anders Hermanrud, geotechnical advisor at NGI.
Based on experience and older standards, 100 kg of lime-cement per cubic metre was initially considered necessary to achieve the required strength and stiffness.
“When we tested the first columns in the field, we found that we could reduce the binder content to 70 kg per cubic metre. We therefore installed 3,200 columns with this mix,” says Hermanrud.
Because the construction progressed in stages, it was possible to test whether the binder content could be reduced even further. After approximately eight months of curing, samples were taken from the lime-cement columns in the field through collaboration between Veidekke’s excavation teams and NGI’s geotechnical specialists. The samples were then tested in NGI’s laboratories. The tests showed that both strength and elasticity remained high—well above the design requirements.
“For the remaining 2,390 columns, the binder content was therefore further reduced to just 50 kg per cubic metre,” says Hermanrud.
Testing paid off
NGI estimates that if all columns had been constructed with 100 kg per cubic metre, the binder cost alone would have exceeded NOK 2.5 million. Instead, the final cost amounted to just over NOK 1.6 million, including sampling and testing.
“The result was a 36% reduction in binder costs compared to relying solely on experience-based values without testing,” says Hermanrud.
Optimizing binder use also has clear climate benefits. If all columns had used 100 kg per cubic metre, emissions from binder production alone would have reached 744 tonnes of CO₂ equivalents—equivalent to 465 return flights between Oslo and New York.
“In reality, emissions from binder production were reduced to 449 tonnes of CO₂ equivalents. Without testing and relying only on experience-based values, emissions would have been 40% higher,” says Hermanrud.
Strong collaboration
Both Veidekke and NGI describe the collaboration as highly successful, based on trust and strong professional expertise on both sides.
“There was a high level of openness and constructive discussions around solution choices. Both parties were able to utilize their expertise, and together we arrived at practical, cost-effective solutions,” says Helgason.
“For us at NGI, this is an excellent example of how we would like our projects to be carried out. We had an exceptionally good collaboration with Veidekke, which resulted in strong solutions and was highly motivating to be part of,” says Magnus Rømoen, NGI’s Project Manager.
The collaboration included dedicated biweekly meetings throughout the project, focusing on construction geotechnics and practical, implementable solutions grounded in theory.
“At Veidekke, we were receptive to input and willing to invest in testing in order to realize the benefits. Adjustments were made that had a positive impact on both progress and cost,” says Helgason.
He adds that for Veidekke as a contractor, the main motivation for innovation was to save time—and thereby money.
“But it is a clear advantage when the benefits can also be measured in environmental terms.”
Helgason believes the project demonstrates the value of close collaboration between contractor and consultant from an early project stage.
“Together, we can leverage expertise across organizations.”
Work in the excavation had to be carried out in stages, allowing testing in NGI’s laboratories to assess whether the binder content in the columns could be reduced. ( Photo: NGI)
