Monitoring the deformation of a temporary top heading invert using Time Domain Reflectometry / Überwachung der Deformation einer temporären Kalottensohle mit Time Domain Reflectometry

For the objective evaluation of the structural safety of tunnel structures during the construction phase, continuous monitoring of all important structural elements (e.g. tunnel lining) and the tunnel face are of utmost importance. The temporary top heading invert, frequently used in sensitive areas of top heading drives, could not up to now be monitored with measuring equipment, because it is usually covered with infill to form a temporary haul road.
The application of a Time Domain Reflectometry (TDR) measurement system makes it possible for the first time to detect, localise and quantify failures in the shotcrete lining. The calibration of the TDR measurement system in laboratory tests and the experience gained through a practical trial in the Lainzer tunnel in Vienna have made it possible to determine the capabilities and limits of this measuring system and demonstrate its readiness for practical use.