During routine 5-year inspection for Rv. 706 Strindheim tunnel, irregularities related to the rock protection and rock conditions were discovered.

Following discoveries of cracks and deformations in the rock and spray concrete, extensive special inspection, ongoing prism and shaking measurements and reinforced inspection regimen from the contractor and geologist with weekly checks were implemented. The price measurements measure movements with very high accuracy. The special inspection was recently completed.

The tunnel is safe for traffic

- After the first findings, it has worked intensively to map and monitor the condition. We emphasize that the tunnel is safe for traffic. However, Statens vegvesen (the Norwegian Public Roads Administration) wants to make the improvements as soon as possible so that this does not develop further. Safety comes first, says section manager for Maintenance in Central Norway Johnny Skår.

The special inspection has revealed that the rock protection through bolting and spray concrete is not sufficiently dimensioned for the rock conditions. Between the rock/rock protection and the tunnel run itself is prefabricated concrete vault. It is emphasized that no cracks have been found in the concrete elements of the tunnel vault. The rock conditions were mapped as demanding before the tunnel was built, but the surveys indicate that there is a larger element of soapstone than previously assumed.

- Kleberstein is challenging as this rock has lower strength and deforms lighter than other rocks. This makes it more challenging to stabilize the tunnel run with traditional methods such as spray concrete and bolting. The problem area is limited to about 50 meters in length in the soap zone, Skår points out.

The special inspection, the prism and shaking measurements and the reinforced weekly control regime mean that Statens vegvesen has a very good and continuous overview of the condition of the cracks and deformations.

- Limited findings have been made in both tunnel runs and in cross -connection 4. There is automatic notification associated with the shaking measurements, while the price measurements are read by manually according to established routine. Combined with weekly inspections, we now have a good overview of cracks and deformations and do not have tracked changes in significance after measurements and controls started, Skår emphasizes.

Works with planning repair measures

Parallel to the mapping work, preparatory work has been done on planning and planning of repair work in the form of extended hedging. A work has also been started on assessing and finding traffic solutions when these work is to be performed. Both related to inspection results and planning/design are used by third -party control via a consultant.

- The Strindheim tunnel is high -traffic with the traffic of an average of 23,500 vehicles a day, and the bypass options are poor. Construction implementation requires the closure of individual races and leads to a challenging traffic situation, says Skår.

All necessary resources are mobilized and the work on planning/design, contract process and traffic solutions are top priority. The goal is an efficient and time -limited implementation, where the traffic challenges are limited, while at the same time the hedging work gives a good and lasting result.

- The work will nevertheless start in the mid or late March, and will therefore not conflict with the Ski World Cup that ends on March 9, Skår emphasizes.

Statens vegvesen has informed Trøndelag county council and Trondheim municipality on the status of the Strindheim tunnel, and will also involve the emergency services. Given the challenges related to construction implementation, detour and impact on traffic flow, a working group of road owners will have a continuous and close cooperation in the future.

Statens vegvesen will return with information when design/planning is completed and you know more about the traffic consequences.

About the tunnel

The Strindheim tunnel goes from Nyhavna in Trondheim to Strindheim in the roundabout at the circus shopping. The tunnel was opened on June 24, 2014. It has a ÅDT of 23,500 (vehicle a day). The tunnel is a two -run tunnel that is 2.6 km long and has two lanes in each tunnel run. When the tunnel of the tunnel, detour is very challenging.

Foto: Erlend Karlsen/Statens vegvesen.

Source: Statens vegvesen press release.