The Engelberg Base Tunnel, completed in 1999, shows severe deformations and damages of the inner lining. They endanger the stability of the tunnel over a length of 180 metres in the west tunnel and 170 metres in the east tunnel. The damaged tunnel section is located in the layers of the unleached gypsum keuper. Amberg was commissioned with the object planning and the structural design for the necessary refurbishment.

The main challenge in the project is the anhydrite-bearing, swellable rock. An additional facing layer, the optimisation of the roadway slab and the installation of an intermediate slab will horizontally reinforce the heavily stressed sections. Thus, the concept of load transfer in the inner lining of the tunnel will be changed to ensure long-term strengthening.

The object planning and structural design implemented by Amberg took into account the construction work during ongoing operations with over 100,000 vehicles per day.
In addition to the structural reinforcement, an operational upgrade will also be implemented. This includes the conversion of an operating building, the laying of cable runs, tunnel ventilation and the drainage of the structure.

The combination of all the refurbishment measures required a simultaneous, closely interlocking execution of the construction process. Amberg implemented this planning in a very short period of less than eight months. On completion of the project, both tunnel tubes will be state-of-the-art in accordance with the guidelines for the equipment and operation of road tunnels (RABT).

Learn more about the work on the Engelberg Base Tunnel in the article "Engelberg Base Tunnel: Refurbishing the Inner Lining by Completely Changing Load Transference in Swelling Rock – Preliminary Test, Structural and Operational Optimisations".

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