Quick clay is a special kind of clay found in several locations in Norway, especially Trøndelag and eastern Norway. Engineering consultants Aas-Jakobsen in Trondheim commissioned NGI to take care of the geotechnical planning.

In order to stabilise the ground on which the new E6 is to be built at Klett, lime and cement are going to be mixed into more than 44,000 boreholes, each of which is up to 25 metres deep. The combined length of these lime cement piles will be in excess of 900 km, which is more than the distance between Oslo and Bodø in a beeline.

"Building on stabilised quick clay isn't particularly unusual. What is unusual is to do it on such a scale and with such extensive stabilising measures as we are employing here. Lime cement stabilisation has never previously been used on such a large scale in a road project in Norway," says Bjørn Kristian Bache, geotechnician at NGI Trondheim. 

Challenging project

Two large machines will add lime and cement under pressure, then whisk it up with the quick clay.  Then the mixture will be left to set for at least two months. This will secure the subsoil and prevent the quick clay being destabilised by external forces in the future.

A large area at Klett and a smaller area in Storlersbakken will have to be stabilised.  It is 200 metres down to solid ground on parts of the stretch. Without expert geotechnical planning and follow-up, the road project would not have been feasible.

"Just now we are about to raise a small river, the Søra, which runs through the construction area and flows into the Gaula. The river is being given a new, erosion-proof course, which will ensure that there will be no landslides as a result of it eroding the clay slopes. The measure is one of many designed to secure the stability of the area against quick clay slides," Bjørn Kristian Bache explains.

Huge quantities of clay have to be moved, and NGI's experts will be checking on the stabilisation and foundation work as the project progresses. Therefore, Bjørn Kristian and his colleagues are going to be busy for quite some time to come.

The stabilisation work will continue until autumn 2017 when construction of the motorway can begin in earnest.
 

Perspektivskisse fremtidig Klettkryss

This is what the intersection of the E6 and E39 at Klett will look like, including 14-metre cuttings.  (Illustration: Aas-Jakobsen Trondheim)

 

SOME FACTS:

  • Quick clay is a special type of clay that occurs in Norway, Sweden, Finland, Russia, Canada and Alaska below the marine limit (maximum sea level after the last ice age).
  • If quick clay is subjected to stress or agitation as a result of natural or human forces, the lattice structure of the clay can collapse and become liquid. This can lead to massive quick clay slides.
  • Large quick clay deposits of considerable depth make the construction work extra challenging at the Klett Interchange on Trondheim's southern limits, where the E39 from Orkanger joins the E6.
  • The construction work began in April 2016. The lime cement stabilisation work will take until autumn 2017.
  • At total of 44,000 boreholes are being filled with lime and cement in order to stabilise the ground. Each hole is up 25 m deep and has a diameter of 60 cm. Together, the boreholes cover an area of 37,500 square metres.
  • Around 2 million cubic metres of earth will have to be moved before the road project is completed.
  • Peab is the main contractor. Aas-Jakobsen Trondheim is the engineering consultant. NGI has been acting as the geotechnical engineering consultant with responsibility for geotechnical planning.
  • During construction, NGI is providing geotechnical consultancy services, inspection and follow-up in respect of the construction work.
  • NGI carried out extensive field work beforehand, including taking samples and surveying the ground conditions.
  • The total budget for the project is NOK 2.5 billion.

See also ARTICLE on ADRESSA.NO, including video interview with the construction managers at the Norwegian Public Roads Administration and footage shot by drone.