Monitoring unstable rock in a tunnel
Cautus Geo has fitted the Strindheim Tunnel with instruments for automatic and continuous monitoring. Any movements in the rock will be detected immediately.
Problem statement
A special inspection revealed cracks and unstable rock masses in an area of claystone in the Strindheim Tunnel in Trondheim in the spring of 2025. Deformations in the shotcrete and the rock led to the tunnel being closed and extensive repair work being carried out. The Norwegian Public Roads Administration implemented renewed rock stabilisation measures. New monitoring procedures and measures to secure areas of claystone were put in place.
Solution
Cautus Geo has fitted the rock with vertical and horizontal settlement and deformation tubes. Data is transmitted continuously to the Cautus Web analytics platform. An alarm system has been set up there to provide real-time alerts should any new movements occur. This is in addition to manual inspection routines.
The ten-year-old Strindheim Tunnel has two 2.5-kilometre-long tubes. In the spring of 2025, deformations were observed in the shotcrete. A special inspection also revealed deformations in a section of claystone.
The Norwegian Public Roads Administration dismantled the electrical installations, removed wall and ceiling elements, and surveyed the rock behind. Before reopening, the tunnels were secured with reinforced shotcrete arches, shotcrete and rock bolts. Rock was also blasted away to make room for the safety measures, and Cautus Geo fitted instruments to the weak sections for continuous and automatic monitoring.
Closed at night
Cautus Geo installed longitudinal and transverse settlement and deformation tubes behind the concrete in both tunnel tubes. During the work, the tunnel tube was closed and traffic was diverted to two-way traffic in the other tunnel tube. By the start of summer 2026, everything was in place.
Not only does this allow you to access the Cautus Web monitoring solution and view the status in real time, but it also triggers an automatic alarm notification if anything changes in the rock mass.
The monitoring equipment is installed directly on the rock face. Once the stabilisation measures have been completed, the Strindheim Tunnel should be stable. Should any new changes, in the form of movements, occur in the rock, these will be detected and reported in real time.
Customer
Norwegian Public Roads Administration
Year
2026 – Continuous and ongoing
Location
Trondheim
Application area
Technology
Visual inspections are required, but in many areas space is limited and access is difficult. This type of monitoring using instrumentation is a good measure that provides continuous monitoring.
Construction Manager Cecilie Hestås Hove at the Norwegian Public Roads Administration.
Contact person
Switchboard telephone +47 990 96 580 or e-mail salg@cautusgeo.com
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