The improvement of the Strindheim tunnel starts in April

The monitoring has been strengthened, security measures are planned and the alternative for traffic flow is considered. The contract for the improvement is now being tendered.

On January 27 this year, Statens vegvesen (the Norwegian Public Roads Administration) informed the need for improvements to the tunnel, which runs from Nyhavna in Trondheim to Strindheim in the roundabout at the circus shopping, linked to irregularities for the rock protection and rock conditions.

Mobilized necessary resources

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 has lower strength and deforms more easily than other rocks. Inspections show that existing rock protection through bolting and spray concrete is not well -dimensioned for the rock conditions.

- All necessary resources are set to implement this process as quickly as possible as possible, while safeguarding the dialogue with affected parties. Both related to inspection results and the design of the security measures are used by third -party control via a consultant, says Johnny Skår, section manager for maintenance in the middle of Statens vegvesen.

The goal is a fast but also lasting securing of the tunnel.
The tunnel is safe for traffic

No movements have been recorded on the shaking or prism measurements that monitor the safety of the Strindheim tunnel since the reinforced follow-up regime was established. Some further cracks in the spray concrete have been observed via inspections, but these do not represent any further danger.

- We are confident that the repair measures that have been designed will provide a lasting and good securing of the Strindheim tunnel, while at the same time being assured by the current measurements that have been carried out. The tunnel is safe to keep open to traffic as the situation is now, but the new cracks in the spray concrete still show that it is appropriate to make the improvements by the Strindheim tunnel as soon as possible. We must avoid getting into a situation where we suddenly have to close the tunnel if the measurements change, Skår emphasizes.

Weekly inspections, prism and shaking measurements and a 3D scan of the problem areas mean that Statens vegvesen has a very good overview of both the condition and the challenges:

This is to be done

A competitive basis has now been highlighted, based on the projected repair measures.

 - We will be additional to the walls from both sides towards the cross -stroke with long bolts. The crossroads are the escape route between the two tunnel runs. This will strengthen the mountain in the soap zone. In addition, we set up spray concrete arches, where reinforcing bars are fastened with long bolts in the mountain in the outer concrete vault and then sprayed with concrete, Skår explains.

These will be permanent concrete arches that increase the strength of the tunnel profile. Over 40 such concrete arches have been described in the competitive basis. In order to implement the hedging measures, the inner vault of concrete elements must be dismantled before starting work on the concrete arches, and then remounting the concrete vault before the job is complete. This means that all work is done on the outside of the inner concrete vault, and thus is not visible afterwards.

Works with solutions for traffic flow

It has also worked continuously to look at how the traffic flow can be carried out as best as possible while the repair work is carried out. Regardless of the alternative, the traffic situation during the construction implementation will be challenging, Skår points out.

- The preferred option is that we close and work in one tunnel run at a time and run two -way traffic in the other. The tunnel and signage are basically not designed for this, so we work with solutions for this to be done in a traffic -safe way. In any case, this will provide a demanding traffic situation with queues and waiting times, so here we depend on those who have the opportunity to choose other modes of transport and transport routes during the construction period.

Both tracking analyzes and risk assessments related to traffic flow have been created.

- Based on the design and quantity calculations, a progress plan is worked on. We see that at the earliest we can get started in week 15 and there will be a lot of working hours in each race to be completed, as there are extensive measures to be implemented. We still aim to finish the improvements for the summer, says Skår.

A working group has been established with Trøndelag county council and Trondheim municipality to look at the challenges related to construction and traffic congestion, as the security measures touch them as road owners for any detour and related to work they themselves have planned. A meeting has also been held and dialogue has been established with the emergency services.

Statens vegvesen will return with more information when start -up, implementation and traffic flow are finally determined.

source: Statens vegvesen Pressemelding.