The Norwegian Public Roads Administration (NPRA) has published the tender documents for core drilling in the Romsdalsfjord that will serve as preliminary surveys for the 15–16km long subsea tunnel between Vik and Otrøya in Møre og Romsdal county in Norway.‘The drilling operation is spectacular. 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 tunnel is part of the work on a ferry-free E39 road, and the aim is to provide a more predictable and efficient crossing of the Romsdalsfjord together with the large suspension bridge across Julsundet sound. The deadline for submitting tenders is January 30 2015, and interested contractors are invited to take part in an inspection starting from Molde (Norway) on January 14, 2015.
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‘We have great expectations of these surveys, which we believe will be both considerably less expensive and safer than drilling from a ship, as was done on the E39 Rogfast further south on the E39 road in Norway this summer. The island of Tautra means that we can have hopes of drilling very long bore holes and thereby be able to map the whole route of the tunnel. The drilling equipment that will be used must be very powerful and have advanced steering; such equipment may be found in the mining industry, for example in Australia,’ explains Johnsen.
A total of four holes will be drilled under the Romsdalsfjord, with lengths of between 1,500 m and 2,200m from three different drill sites. Two holes will be drilled from Tautra island, one from Otrøya island and one from Vike (see drawing).
Seismic surveys that have previously been carried out have found 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 surveys. Magnetic measurements from a helicopter are now being carried out to find out more about the ground conditions and where we the bore holes are to be drilled.
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.
At the same time, drill cores will be extracted for examination by experts in connection with the subsequent tunnel work. Laboratory tests will also be carried out to determine the rock quality. The quality of the rock determines what the excavated tunnel rock can be used for once construction starts.