Nye Veier has begun using a new, cost-effective method for surveying the subsurface where roads and tunnels are to be built
Nye Veier [Norwegian government-owned company planning, constructing, operating and maintaining major national highways] is underway with five large road projects along the E6 highway in Trøndelag [, a county in Norway]. This is the first time that Nye Veier is using geoskanning in their preparatory work. By using a helicopter and a measurement frame hanging 35 metres under the helicopter that sends electromagnetic signals into the ground, it is possible to map both the thickness and type of sediments and rock in a completely new and more rational way than usual.
Drillings and soil samples are the traditional methods that are most commonly used for mapping ground conditions in Norwegian road building to date. Geoscanning, on the other hand, has been used in connection with mineral exploration, including in Norway.
The electromagnetic signals induce electrical currents in the subsurface that are measured by the instruments mounted on the hanging frame. The system can send signals as far as 300 to 400 meters deep. This information is crucial for mapping the extent of quick clay and the quality of rock units.
“We hope that we will save up to 30 percent of the ground investigation costs by using geoscanning,” reports Kari Charlotte Sellgren, technical lead for tunneling at Nye Veier, to Byggindustrien.
Mapping ground conditions
“Uncertain and unclear ground conditions is one of the costliest and most time-consuming aspects of building roads in Norway today. This is especially noticeable in road construction in Trøndelag, where there are large amounts of quick clay in some aeas . This also applies to ground conditions along many new road alignments where Nye Veier will build in the coming years. Significant savings and access to larger volumes of data are reasons why Nye Veier has increased the focus on geoscanning,” says Sellgren.
“We still depend on some drilling, though to a much lesser extent and with greater reliability than before,” says Sellgren
Using geoscanning nevertheless does not mean an end to all geotechnical drillings.
During the last weeks, Nord Helicopter (based in Ålesund) has flown the stretch from Kvithammar to Åsen where a tunnel more than seven kilometers long with two separate tunnel sections will be built through Forbordfjellet [name of a mountain]. Other segments between Ulsberg and Kvål have also been mapped.
“Along the planned road alignment between Kvithammar and Åsen, especially challenging ground conditions with large amounts of quick clay have been mapped, ” says Sellgren, referring to a 19-kilometer road segment.
After Pentecost, Nord Helikopter and the newly established company EMerald Geomodelling conducted similar measurements south of Trondheim. On the 24-kilometer-long stretch between Vindåsliene to Ulsberg, two locations where tunnels will be built were specifically investigated.
Once geoscanning has started, the ground for two upcoming tunnels and the extent of sediments in the last stretch, Kvål-Vindåsliene, will also be mapped. Planning is also in full swing here.
The newly established company EMerald Geomodelling, which has its origins at NGI (the Norwegian Geotechnical Institute), is behind the new technology and is responsible for interpreting the measurement results that the Danish company SkyTEM collects during the helicopter flights.
“We have developed a technology that makes it much easier than before to get an overview of what the ground conditions are, whether they are sediments or rock,” says Andi A. Pfaffhuber to Byggeindustrien. He was previously head of section for geosurveys at NGI and is currently CEO of EMerald Geomodelling. According to Pfaffhuber, the company is the only one in Norway, and one of the few worldwide, that can offer this technology.
Geophysical and geotechnical data is used to create 3D models of the subsurface. This may include the amount and condition of clay as well as other sediments and also the quality of the rocks through which tunnels are to be built. The use of 3D significantly facilitates work on the design of new roads.