Suomenlinna tunnel, Helsinki

YIT realised the renovation of the tunnel providing municipal engineering to the island district of Suomenlinna in Helsinki with an alliance model.

Suomenlinnan tunnelihanke / Suomenlinna tunnel project
Suomenlinnan tunnelihanke / Suomenlinna tunnel project

The renovation of the tunnel ensured that municipal engineering will continue to function in the sea fortress Suomenlinna without issues in the future. The renovation project ensured the safety of the maintenance staff, decreased the tunnel’s maintenance costs and extended the tunnel’s lifecycle.

The tunnel brings district heating, electricity, water, plumbing as well as telecommunications and TV connections to the island of Suomenlinna. In addition, the tunnel is intended for the use of emergency vehicles.

The rock was compacted and reinforced to avoid seepage water and improve safety. The technical building systems maintaining the tunnel’s own operations and underdrainage were completely renewed. In addition, the project included centralising the municipal engineering systems located in the tunnel, which improved the safety of emergency vehicles in the tunnel. The budget of the renovation was EUR 7 million.

Suomenlinna sea fortress is a UNESCO World Heritage Site loved by visitors but also one of the districts of Helsinki. Approximately 800 residents live on the island, 400–500 people work there, depending on the season, and approximately a million people visit it every year.

In the project, Pöyry was responsible for the planning and YIT for the construction. In the alliance model, the parties to the project were mutually responsible for the planning and implementation, sharing the risks and benefits related to the project.

rock construction

the alliance model


Project name
Suomenlinna tunnel
The Governing Body of Suomenlinna
Project status
Business segment