The Semmering Base Railway Tunnel construction in the province of Styria, Austria is a challenging construction project with numerous unusual problems. This area is characterised by a large-scale fault zone and complex ground conditions. Numerous constraints aboveground, like high-pressure gas pipelines require monitoring and protection measures. The entire construction area is crossed by several gas pipelines with up to 63 bar operating pressure, which are driven over in the long term and passed under by all the underground works.
A distributed fibre optical measurement system for the full-coverage recording of strains in the gas pipelines was installed in collaboration with the Institute of Engineering Geodesy and Measurement Systems (IGMS) of TU Graz (igms.tugraz.at). With this arrangement, longitudinal strains along the entire lines, average strains and horizontal and vertical curvatures can be derived. The fibre optical sensor cables were applied directly to the gas pipes over the entire length of the facilities area of about 320 m in order to guarantee complete transmission of the strains in the line to the glass fibre.
In order to correct the temperature effect on the strain values, additional temperature sensor cables were laid. Altogether about 6.8 km of glass fibre cable were installed in the entire site area for monitoring. The strain measurements have been running since July 2016 with automatic evaluation and alarming. The results are compared automatically with the defined thresholds and if these are exceeded an alarm is activated.