At the large infrastructure projects of the Austrian Federal Railways OeBB in the Alpine region geotechnical structures with different characteristics are encountered. Especially fault zones associated with high overburden are a great challenge during tunnelling, often resulting in large deformation of the rock-support system. On the other hand support for tunnels in swelling ground has to be designed to an expected swelling pressure during the life time of a tunnel. The goal is to apply robust, reliable and durable monitoring systems for observing such geotechnical structures during a service life of the tunnels of 150 years. The benefit is to early detect unfavourable tendencies of the system behaviour and the planning of measures in terms of predictive maintenance accordingly in due time. Finally this ensures high availability of the tunnels during operation. The paper presents the implementation of long-term monitoring via the projects Koralm Tunnel, Granitztal Tunnel and the Semmering Base Tunnel.
Fault zones associated with high overburden are a great challenge during tunnelling and often result in large deformations of the rock-support system. On the other hand the potential of swelling ground is another problem. Although the support is designed due to the expected ground pressure uncertainties in terms of the further development of loads acting on the tunnel during its operation and lifetime still remains. This is where the strategy of the Austrian Federal Railways OeBB starts to apply long-term observation of a tunnel in selected sections in weak rocks or fault zones. The main goal is to identify unfavourable tendencies in the displacement characteristic as well as the development of stresses in the tunnel lining. Based on the respective geotechnical situation targeted measures in the sense of predictive maintenance can be planned in due time. This ensures to reduce operational restrictions to a minimum and the highest possible tunnel availability. In order to achieve this ambitious goal, appropriate monitoring concepts and methods for the observation of the inner lining are already developed and implemented. In the following aspects of long-term monitoring are outlined via the projects Koralm Tunnel (KAT), Granitztal Tunnel (GTT) and the Semmering Base Tunnel (SBT). Successful long-term monitoring installations required the involvement of all stakeholders at an early stage. During the planning phase, the position of the monitoring equipment has to be aligned with the location of other tunnel infrastructure like conductor rails, handrails, emergency lights etc. Otherwise, measurements may not be possible, e.g. levelling staff cannot be setup due to handrail, or sensors may be destroyed for instances by drillings for the conductor rail mounting. Furthermore, a close collaboration with the tunnel design engineer can utilize synergies, like using communication cables also for the transfer of sensing data. During the construction, an ongoing coordination with the construction company is required to minimize interference of sensor installations with the construction process and to guarantee a high sensor survival rate.
