Landslide Caused Damages in a Gallery

• Published in: Rock mechanics and rock engineering Vol. 49; no. 6; pp. 2301 - 2315
• Main Authors: Poisel, R., Mair am Tinkhof, K., Preh, A.
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01-06-2016; Springer Nature B.V
• Subjects: Civil Engineering; Cracks; Damage; Earth and Environmental Science; Earth Sciences; Galleries; Geophysics/Geodesy; Landslides; Landslides & mudslides; Mathematical models; Original Paper; Plate tectonics; Shotcrete; Slopes; Tunnels; Valleys; Landslide caused damages underground; Deep seated landslide; Tunnelling; Tunnel damages
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-015-0765-3

On October 5th, 2010, cracks were found in a gallery 1.8 m high and 1.4 m wide. The gallery is 100 years old, runs parallel to a valley flank and was excavated in a tectonically strongly stressed, weathered and slightly dipping sandwich of clayey shales, sandstones and marls. The cracks in the roof as well as in the invert ran parallel to the axis of the gallery. Monitoring showed that crack widths were increasing 1.5 mm per year, sidewall distances were increasing 3.5 mm per year, whereas the height of the gallery was decreasing 2.5 mm per year. After eliminating several possible causes of cracking, a landslide producing the damages had to be taken into consideration. Monitoring of the valley flank surface as well as inclinometer readings revealed that a landslide was occurring, loading the gallery lining. Most probably the landslide had been reactivated by excessive rainfall in 2009 as well as by works for the renewal of a weir in the valley bottom. As stabilization of the slope was not an option for several reasons, it was decided to replace the gallery by a new one deeper inside the slope, which will be ready for operation in 2017. Thus the old gallery has to be kept in operation till then and it was decided to reinforce the old gallery by a heavily reinforced shotcrete lining 10 cm thick. As slope displacements went on, cracks in the shotcrete lining developed with a completely different pattern: in the section where the gallery lies completely in the landslide shear zone no cracks formed until now due to heavy reinforcement, whereas in the transition sections stable ground–landslide and landslide–stable ground diagonal tension cracks in the roof due to shear by the landslide developed. Numerical models showed that cracking and spalling of the shotcrete lining would occur only after some centimetres of additional displacements of the slope, which hopefully will not occur before 2017.