The Päijänne Tunnel conveys raw water from Lake Päijänne to the Helsinki metropolitan area. At 120 km, it is one the world's longest continuous rock tunnels. The tunnel lies a depth of 30-100 meters below ground level. The cross section of the tunnel is 13.5-18 sq.m. The tunnel has been water filled since its completion in 1982.
The renovation work includes scaling, shotcreting (160 000 sq.m), bolting (10 000 bolts) and grouting. The renovation work also includes emptying of the tunnel section by pumping 1.1 million m3 of water. The work will be done via 10 access tunnels.
In connection with the renovation work four new access tunnels will be excavated using the drill and blast method. The combined length of the new tunnels is about 140 m and they will have a cross-section of about 21 sq.m.
The Päijänne tunnel is in its entirety situated in hard rock, mostly granite and gneiss.