The refurbishment strategy of the Seelisberg Tunnel

The 9.25 km long, twin-tube Seelisberg Road Tunnel was constructed between 1972 and 1980. The construction of its middle section posed critical problems. Damages on the tunnel segments and failures of the lateral bearings of the intermediate slab elements appeared in a short delay of time. Several series of extensive investigations and multiple series of measurements followed over the years. The investigations concluded that the damages were directly related to movements of the tunnel segments, since the excavation method had created a considerably larger profile, resulting in insufficient bedding of the concrete segments. Several immediate campaigns of interventions were taken to secure the slab and finally the voids behind the tunnel segments were filled, as a provisional safety measure. Parallel to these ongoing works, an overall project of refurbishment for the whole tunnel, including a replacement of segments in the middle section was developed. This project was thoroughly scrutinized by the Federal Roads Office and refused. The report concluded that filling the voids behind the segments had resolved the major static deficits. The new orientation for the refurbishment actions became the evaluation of each construction component. The most urgent tasks will be executed from 2013 to 2015.