Monitoring the Opera Tunnel

The foundation work for a new school at Sørengautstikkeren in Bjørvika, Oslo, involves work in the ground close to the two runs of the Opera Tunnel from east to west. Cautus Geo is monitoring the ground conditions outside and has also instrumented inside the tunnels.

- Sheet piling is now underway for the new school. This will continue until March. Then there will be piling from May to November. Construction work will continue until school starts in the autumn of 2028," says project manager Tore Dahl of Oslobygg KF, the developer of the new school and multi-purpose hall.

Lots of instrumentation

Cautus Geo automatically and continuously monitors ground conditions. It will continue for five years. The instrumentation is extensive. In addition to deformation monitoring inside both tunnels, the ground outside is also monitored with pore pressure gauges and borehole extensometers.

- The instrumentation ensures automatic and continuous measurement and sends data in real time to Cautus Web. An alarm has been set up with SMS and e-mail notification if changes occur in the ground conditions outside the heavily trafficked Opera Tunnel. The same happens if changes are detected inside the tunnels," says Atle Gerhardsen, CEO of Cautus Geo.

Cautus Geo has also previously secured the Opera Tunnel, including when the museum extension was built in 2019.

Control during construction

- The purpose is to monitor and control any movements in the tunnel in connection with the construction work. "We've installed two automatic settlement profiles inside the tunnels, one in the eastbound and one in the westbound direction. Each of the profiles mounted on the walls is 216 metres long," says operations manager Sigmund Brekke Langelid of Cautus Geo.

- It's all about safety. "We'll be working right next to the tunnel. The distance is down to 3-5 metres. This means that work must be stopped if there are changes in the ground conditions and pore pressure that affect the tunnel. Then we have to find out what we can do to avoid settlements," says Dahl.

School and new meeting place

Bjørvika school and multi-purpose hall, totalling 15,000 square metres, will be a new meeting place. It will link the Sørenga area with Gamlebyen and Grønland. The building is dense, but inviting.

- The school will create a sense of community and be a good place for everyone. It will have a multi-purpose hall and will also be a playground for everyone involved in non-organised activities. The roof will be an open space in line with the Opera Roof and Økern Portal.

- The Norwegian Public Roads Administration has set requirements for monitoring. If limit values are breached, an alarm is sent to the Norwegian Public Roads Administration, the contractor and us as the developer," says Dahl.

Instrumentation

• SAA deformation cables measure movements in both runs of the Opera Tunnel with high accuracy.
• Pore pressure gauges and borehole extensometers have been established in the ground outside the tunnels.
• Automatic logging system manages data capture from an extensive sensor network inside and outside the tunnel.
• Cautus Web continuously analyses recorded data and sends notifications if set limit values are breached.