Instrumenting the Bergås tunnel on the E6 motorway

Work on the new Bergåstunnel on the E6 Helgeland motorway could resume just after Easter. Work was halted just before Christmas. The reason was undiscovered loose material 600 metres inside the tunnel.

The Bergås tunnel in Grane municipality will be two kilometres long. The work was stopped 600 metres inside the mountain. The tunnel is part of the 10.5 kilometre E6 project from Svenningelv to Lien. It is scheduled to open in autumn 2025.

It was a big surprise when work had to be stopped just before Christmas in December 2022.

- Ground surveys prior to the start of the work did not reveal the soil. They showed poor quality rock in six different zones. The third turned out to consist of moraine masses," says project manager Bård Nyland of the Norwegian Public Roads Administration.

- "We're using our experience from the Kronstadt tunnel in Bergen. There, too, the challenges posed by loose soils were considerable. We moved the instrumentation as the work progressed. Now we're going to do the same in the Bergås tunnel," says COO Atle Gerhardsen of Cautus Geo.

Tromsø office

Håvard Hind manages the Tromsø office of Cautus Geo. It is he who is leading the work of setting up the monitoring inside the tunnel.

- We are installing deformation hoses (SAAV) of just over 30 metres in boreholes along the tunnel roof (suspension) of the planned tunnel. This provides automatic and continuous monitoring. We produce a 3D model of the borehole every ten minutes and can establish alerts if defined threshold values are exceeded," says Hind.

- "We're installing more than SAA and will be moving the instrumentation into the mountain as the work progresses, after it resumes over Easter," says Hind.

LNS with turnkey contract

The construction company LNS (Leonhard Nilsen & Sønner AS) has been awarded the turnkey contract for the E6 Helgeland motorway, which is currently under construction. The turnkey contract is worth NOK 1.1 billion, excluding VAT.

- "Even though the work in the tunnel has been stopped while we establish the instrumentation and plan the further progress, which will provide a safe working environment and secure the progress of the tunnel work, work continues on the E6 section outside the tunnel," says project manager Bernt-Jøran Reinholtsen at LNS.

The section is a complex project, including several bridges.

- "In isolation, the Bergå tunnel will not delay progress. The tunnel work is not currently on a critical timeline," says Reinholtsen.

Important instrumentation

- The work must be carried out in a safe manner. "We need measuring instruments and other equipment to be able to react to any movements in the masses. Between now and Easter, we'll spend the time planning a safe implementation," says Nyland of the Norwegian Public Roads Administration.

The method to be used has been clarified together with the contracting company LNS. "We're doing it in the same way as for the Joberg tunnel in Hardanger. It was opened in 2017. In that case, 100 metres were built in loose masses," says Nyland.

Engineering geologist Bent Aagaard of Aagaard Geo Consulting has been engaged as an expert by LNS consultant Aas-Jakobsen Trondheim AS.

- Instrumentation from Cautus Geo provides instant results online. "We get measurements every half metre in a long and critical profile directly above the tunnel and can also set it up with alerts. That's exactly what we need in the Bergås tunnel," says Aagaard.

The main elements of the E6 Helgeland development package

• Construction and refurbishment totalling NOK 9.5 billion (2022 NOK)
• The route is approximately 260 kilometres long
• In total, approximately 142 kilometres of road are being built and improved
• After repairs, the E6 will be shortened by 6.2 kilometres
• Municipalities: Grane, Rana, Vefsn, Hemnes in Nordland