Tunnel inspection: clearance measurement before route approval


Austrian Federal Railways (ÖBB)

Task definition

Control measurement prior to obtaining track approval


  • Recording with the SPACETEC TS3
  • Express assignment

The measurement task

The client was carrying out renovation work on an existing tunnel in the route network. This included maintenance work on the tunnel structure as well as redesigning the track bed.

The track axis was optimised due to the limited clearance conditions in the old tunnel structure. The adjusted track position aimed to resolve the problem of constrictions while ensuring a comfortable and smooth journey.

There are many parameters to consider when calculating the route a track should take. We use sophisticated software packages for this, and simulation tools help identify the impact of changes in advance.

Before resuming train services, it is still important to confirm that there are no constrictions which could hinder safe operation.


Seamless integration in the project schedule

The time available for the recording was planned in accordance with the schedule of the construction project. Control measurements can only be performed once all work which could affect clearance has been concluded. Machines and construction materials which could obstruct the view of the intrados of the tunnel must be removed from the tunnel. As the section of track had to be approved as quickly as possible after the completion of the work, measurements needed to be timed precisely between these processes.

The measurement results documented the condition upon completion of the work. The results also aimed to ensure that approval was only granted once it was determined that there were no critical constrictions in the tunnel. This means, the scan data had to be evaluated immediately after collection. The clearance space was evaluated so quickly that the results were available the next day even before rail services began running.

The green colours in the clearance profile map indicate that the minimum permissible distances between the vehicle profile and the tunnel profile have been observed.