Rantatunneli is a project of moving highway 12 into a tunnel in the city of Tampere. The excavation work was finished in the summer 2015. The tunnel will be operational in 2017. The twin tunnel will be the longest highway tunnel in Finland with the length of 2.3 kilometres. The project included in-situ stress measurement campaigns, stability analyses and rock displacement monitoring during the excavation phase. The stress measurements were conducted with hydraulic fracturing method. In this paper, the test results and their analysis are presented. Comparison of the predicted and the observed displacement behaviour of the rock mass are discussed.
The city of Tampere, which is the third largest city in Finland, is located on an isthmus between two lakes and thus space is limited. Tampere is also a national traffic nexus as it houses key rail and road connections including three national highways and Helsinki-Oulu railway. All these have originally run through the city center, but two highways have so far been partially rerouted to a ring road running south of the central isthmus. The Rantatunneli project aims to transfer the third highway, national Highway 12, into a tunnel under the city centre. After completion, the tunnel will free up the land on central Tampere northern areas for urban development. The excavated rock is used to fill in the water body for a new park in the future Ranta-Tampella district.
Rantatunneli is built as 2.3 km long twin tunnel which will be the longest highway tunnel in Finland. The tunnel starts from Santalahti in west and ends at Naistenlahti in east. A short concrete tunnel section is built at Santalahti. The tunnel passes under Tammerkoski rapids at midway, and houses a space reservation for a possible underground junction. The span of a single tunnel is 13... 15 m and height 9,2 m (Figures 1 and 2). The thickness of rock cover varies from 8 to 27 m (Figure 3). The total excavated volume for the two tunnel tubes is 650.000 m3. The project was realised as an Alliance scheme between the key organisations, and the design work started in July 2012. An overall cost target was set in mutual understanding. The construction works started in autumn 2013 with excavation of the access tunnels. Tunnel excavations were finished by Midsummer 2015. The construction work is currently in progress, and the tunnel is scheduled to open to traffic in November 2016, few months ahead of schedule. The work will continue after this with construction of a new multilevel junction at Santalahti, landscaping and finishing works. The project is to be completed in 2017.
