ABSTRACT
Tunnel excavation with a tunnel boring machine (TBM) in conjunction with a watertight onepass lining consisting of reinforced precast concrete elements has proven to be an effective and economic tunnelling technique for long tunnels in shallow overburden. Within the last decade this method has been applied in the biggest tunnel projects such as the Channel Tunnel, the Boston Outfall Tunnel or the Great Belt Tunnel. Shielded tunnel boring machines have been used under soft ground conditions as well as under hard rock and mixed ground conditions.
For the application of this successful tunnelling technique under high overburden, e.g. for construction of transalpine tunnels, enormous rock stresses and water pressure have to be considered. By deformations the initial stress conditions are changed and arching effects are produced around the opening. Because of this so called “self bearing capacity of the rock mass”, the excavated cavity can be stabilised by the tunnel support. Since conventional segmental linings are stiff structures, which already allow almost no deformations, new developments must be performed to guarantee sufficient deformability and the stabilisation of the tunnel. Similar to the segmental lining, the tunnel boring machine has to be deformable to prevent from getting stuck. Waterproofing gaskets also have to be adopted to the changed conditions to provide a dry tunnel.
The international EUREKA project “CONTUN” aims at the development of such deformable TBM’s and linings together with a suitable sealing system. Austrian consulting company, D2-Consult is responsible for the co-ordination and the development of the deformable lining system, German TBM supplier Herrenknecht works for solutions for deformable tunnel boring machines, while German company Phoenix and Swiss company Dätwyler deal with development of new gasket types.
