On the west coast of central Norway the Norwegian Public Roads Administration (NPRA) is carrying out a core drilling operation for a 15,5 km long subsea tunnel.

Seismic surveys that have previously been carried out shows weakness zones in the rock that the tunnel must be drilled through. There may also be smaller zones and cracks that are not identified by the previous surveys.

The purpose of the core drilling is to gain more detailed knowledge about these assumed weakness zones and more certainty in relation to identifying the rock surface before finally deciding the route of the tunnel.

“As far as we know, this is the longest core drilling hole that has ever been drilled in mainland Norway,” says project manager Harald Inge Johnsen.

The core drilling is preliminary surveys for a possible subsea tunnel under the Romsdalsfjord in an effort to meet the government’s ambition to make the Highway Coastal Route E39 ferry-free. The project also includes a 1960 m suspension bridge with a 1600 m span.

Earlier in March, The Norwegian Public Roads Administration signed a 60 million NOK contract with Entreprenørservice AS for pervasive core drilling along the entire route of the tunnel.

A total of four holes will be drilled with lengths between 1 500 m and 2 200 m from three different drill sites. Two holes will be drilled from the island Tautra, one from Vik and one from Otrøya.

The core drilling started at Otrøya on April 1 with equipment from subcontractor Asera Mining AB. Entreprenørservice shall drill the two holes from the island Tautra. Devico AS is responsible for the steering of the drilling. The drilling operation will continue for a year until March 2016.

“We have great expectations for the challenging drilling, which will identify weakness zones in the bedrock. Hopefully the island Tautra makes it possible to drill very long holes and thereby be able to map the whole route of the tunnel,” says Johnsen.

Image: NPRA