Building on peatland with a lighter touch
Peatlands store carbon, regulate water and are home to species adapted to a highly specialised environment. When essential infrastructure has to cross a bog, research, careful design and long-term monitoring can reduce the environmental risk, both for nature and for the project itself.
Excavators spread sand over geotextile and geogrid at Kringelmomyra. Ground mats spread the load so the machines do not sink into the soft bog. ( Photo: NGI)
– Coming from Costa Rica, I feel the same sense of nature’s fragility and importance in Norway’s peatlands as I do in the rainforests back home. They have almost the same status, says Priscilla Paniagua, Lead Engineer at NGI’s office in Trondheim.
The comparison is apt. Peat builds up extremely slowly in waterlogged conditions. With little oxygen available, plant remains decompose slowly and the carbon stays locked in the ground. A bog is therefore both an ecosystem and a natural archive that has formed over a very long time.
– Peat grows by about one millimetre a year. If you’re standing on five metres of peat, you’re looking at 5,000 years. When the peat is dug out, the carbon store is removed from the site. How much of that carbon is eventually released depends on how the peat is handled, she says.
Half a metre of peat represents several hundred years of stored carbon. A bog also tells the story of how vegetation and landscape have changed over time. That is why the first choice is simple, Paniagua stresses:
– The starting point must be to avoid building on peatland. But sometimes the route has already been decided, or critical infrastructure has to go ahead. Then we need to know how to keep the impact to a minimum, she says.
Building on ground that is almost water
To a geotechnical engineer, peat is an unusual and challenging material. It holds large amounts of water, has low strength and can keep deforming long after a load has been applied.
– Peat is extremely water-rich and has low shear strength, which makes it difficult to handle and design for in the same way as ordinary soils, says Paniagua.
The traditional solution has often been to dig out the peat and replace it with stronger material. That can make construction easier, but it also removes the carbon store and destroys the bog’s hydrology and natural value.
At Kringelmomyra in Grane municipality, Helgeland, the Norwegian Public Roads Administration and its specialist partners chose a different approach for a new section of the E6: the road was built on top of the bog, leaving the peat in place. NGI designed the solution, led by Bjørn Kristian Fiskvik Bache. A geotextile and a reinforcing geogrid were laid directly on the ground, followed by gravel and rock placed in layers of around 75 centimetres. After each layer, the team waited before adding more:
– You put down a little material, wait, add a little more and wait again. That gives the bog and the ground beneath it time to gain strength, she explains.
This preloading went on for about two years before the road was completed. The aim was to compress the peat gradually to roughly half its thickness without the ground giving way. The method is often called a floating road, although the road does not literally float. It is carried by the combined action of compressed peat, geogrid and fill.
– At first the bog settles quickly. Then it slows down. That’s why we have to monitor it all the way, says Paniagua.
Fill is placed in layers on top of the geotextile and geogrid. After each layer, the team waits so the bog has time to settle and gain strength. ( Photo: NGI)
Monitoring groundwater and vegetation
But what actually happens to a bog when a road is built on top of it? Paniagua and colleagues from organisations including the Norwegian Institute for Nature Research (NINA) and the Norwegian Public Roads Administration have investigated exactly that at Kringelmomyra. The results were published in the scientific journal AIMS Geosciences in 2025.
The study combines geotechnical investigations with monitoring of groundwater and vegetation. The researchers found complex layering: several metres of peat over sand and thick layers of marine clay. In some areas there is also sensitive clay.
– The first measurements showed little impact on groundwater in parts of the bog. But there is a limitation: it is too early to know how the road will affect hydrogeology, vegetation and carbon storage in the long term. Carbon exchange at the site has not been measured either. Long-term monitoring is therefore essential, says Paniagua.
This is also at the heart of NGI’s role. At Kringelmomyra, the institute helped develop the method together with the design-and-build contractor, and is responsible for instrumentation and settlement monitoring along the route. NGI’s expertise was central throughout the project, from mapping peat thickness and the underlying soil layers to sampling and laboratory characterisation. NGI was responsible for designing the road solution and for following up settlement and groundwater levels both during and after construction.
– NGI can deliver the entire design, from site investigations and material characterisation to instrumentation and monitoring, says Paniagua.
Learning from roads already built
Further north, on the 82-kilometre Hålogalandsvegen road between Harstad and Sortland, a completely different approach is being tried. Here the route crosses peatland in several places, and the contractors Skanska and Vassbakk & Stol have tested whether a bog can be moved at all. Almost 11,000 cubic metres of peat were excavated from other parts of the project and transported to Torvmyra beside the road, where a new bog with the right water level was built.
In total, around 8,500 square metres of peatland have been restored or newly established in the project, according to Skanska. In the new bog, vegetation mats from the original bog have been laid back over the peat. The work won the Norwegian construction industry’s climate award, Byggenæringens klimapris, in 2025.
The project is being carried out with the Norwegian Public Roads Administration, while Sweco, NINA and NGI have provided research and specialist support. The new bog will be monitored with sensors for five years. NGI is responsible for the hydrogeological measurements, and its instrumentation department installed and operates the field equipment. Kristoffer Heian has led this work together with several NGI colleagues. NINA is carrying out the carbon measurements.
NGI became involved because Skanska had followed the Norwegian Public Roads Administration’s monitoring programme at Kringelmomyra.
– Skanska came to us and said they wanted to set up a similar monitoring programme. They also had to cross peatland, but they did it differently from the way we did it at Kringelmomyra, says Paniagua.
Along Hålogalandsvegen, the road also crosses three peatlands in different positions: one where it runs straight through the bog, one where it lies downstream and one where it lies upstream. This allows the researchers to compare how the road affects peatland in three different hydrogeological settings.
Another difference is how the data are collected.
– On Hålogalandsvegen everything is connected to a real-time system through NGI Live, so we can monitor the area continuously. At Kringelmomyra we have to take readings on site, which has drawbacks: we risk losing data, and we depend on there being no frost and on being able to reach the sensors, she says.
The Skanska project should not be seen as a general licence to move peatland. Avoiding the intervention is still the best option. In 2025, the Norwegian Environment Agency, on behalf of two ministries, sent a proposal to ban building on peatland out for public consultation. Almost 300 municipalities, organisations, businesses and individuals responded. In January 2026, the agency submitted its summary of the consultation to the ministries, recommending that the proposal be upheld.
Paniagua stresses that systematic monitoring can show which solutions actually work when an intervention cannot be avoided. At the same time, she emphasises that peatland must be understood as a unique, living system.
– When we build on peatland, we need to shift our perspective. It’s not just about keeping the road standing. We also need to understand what happens to the groundwater, the carbon and the surrounding nature, and what consequences such interventions have for the climate and the environment, she concludes.
References
Long, M., Paniagua, P., Grimstad, G., Sponås, E. B. A., Bjertness, E., & Ritter, S. (2023). Behaviour of 60-year-old trial embankments on peat. Engineering Geology, 323, Article 107226. https://doi.org/10.1016/j.enggeo.2023.107226
Paniagua, P., Bache, B. K. F., Stenger, S. R., Kyrkjeeide, M. O., Slettum, E. J., & Long, M. (2025). Characterization of the Kringelmomyra peatland: Geotechnical, hydrogeological, and ecological aspects. AIMS Geosciences, 11(3), 686–703. https://doi.org/10.3934/geosci.2025029
