Spalling along the Bedretto adit, showing (left) a close-up of the spall notch tip, and right,
full sidewall spalling along the tunnel (Huber 2004).
Project Framework and Goals
The Furka-Oberalp railway line presents the only year-round east west connection in the Swiss Alps. It serves to link the resort areas of Valais, Central Switzerland, with those in the Grisons, as well as efficient local transportation. Construction of the Furka (Base) Tunnel began in 1972 and was completed in 1982. To help speed up the construction time in the region of the difficult geological and hydrogeological conditions, an access adit was constructed from the Bedretto Valley. This adit was also an optional rail link to the south that was never established. The adit starts in the south passing through a large toppling landslide mass and intersects the the Rotondo Granite until it meets the Furka Tunnel after a total length of 5.2 km. Significant spalling during construction was observed in the Rotondo Granite and this spalling activity continues to this day (Figure 1).
It is hypothesized that the continued spalling and micro-cracking activity is driven by fluctuations in the relative humidity, which goes from ambient to nearly 100% with each passing train. Such fluctuations could create conditions for a phenomena known as stress corrosion which can occur at crack tips and causes continued crack growth with time. A monitoring system, including a weather station, acoustic emissions sensors, crack moisture sensors, and crack meters will be installed in the summer of 2017 (participation optional, but encouraged). Experiments to control the relative humidity conditions throughout the summer and continued monitoring throughout the rest of the year will be conducted. This thesis will include analysis of the monitoring data and numerical modelling in order to back-analyze the validity of the hypothesis.
Supervisors: Matthew Perras (matthew.perras@erdw.ethz.ch), Kerry Leith
Recent Comments