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August 2020

Keeping the World’s 6th Longest Tunnel Construction Project On Track

The Koralm Tunnel, the sixth-longest railway tunnel in the world, forms a 32.9 km long section of the new 130 km long Koralm Railway, which on completion will connect the Austrian cities of Graz and Klagenfurt in the southeast of the country.

Click here to jump to the testimonial statement.


The new railway line will comprise 47 km of tunnels, have over 100 bridges and 23 modern railway stations and stops along the route. The project is being hailed as one of the most important transport infrastructure projects currently underway in Europe. The construction of the project is due to be completed by 2023 with the route being fully operational by 2025.

The Koralmtunnel KAT3 construction lot recently broke through completing the last of Koralm Tunnel drives in St. Paul im Lavanttal, Carinthia, Austria. A Herrenknecht 9.94 m diameter Multi-mode TBM was used. This type of machine has the capacity to operate in both EBP and open modes to cope with changing ground conditions along the drive. This particular length of tunnelling work covered the final 10.474 km of the tunnel and included a curve with a minimum radius of 3,000 m. The drive commenced in October 2015 and was recently finish on the 17th of June 2020.

The multi-mode design of the TBM was necessary because for about the first 4 km of the drive the TBM drove through sedimentary rocks of the Neogene period and through the Laventtal main fault zone in EPB mode. In June 2018, after two months of conversion work, the TBM started driving the remaining 6 km (approximately) in the open hard rock mode.

The construction site is owned and managed by major infrastructure contractor PORR which has had a long-term relationship with both Herrenknecht and VMT in connection with other tunnelling projects.

To support tunnelling, VMT supplied the necessary navigation and other site management systems including TUnIS Navigation TBMLaser system alongside TUnIS Navigation Office software, VMT’s  TUnIS Ring Sequencing system, SLuM Ultra (VMT’s Automatic Tailskin Clearance Measurement System) and VMT’s RCMS (Ring Convergence Measurement System). The VMT systems were purchased as part of the TBM contract and mainly installed during the machine build. The RCMS system was installed later during the course of 2019.

VMT engineers also provided on-site training for project staff during the course of the project as well as the purchasing of spare parts when required for the navigation system.

The site team also worked with the VMT team to site test various other VMT products which included the new central box LDT.connect and the ELS3G target unit.



Testimonial Statement from Joachim Geißbauer, site manager for KAT3



“Koralm Tunnel Construction Stage KAT3: 10,500 m through most difficult geology

The task

The Koralm railway is part of the new southern railway line. The heart of this new line is the approximately 33 km long Koralm tunnel which connects the two provinces of Carinthia and Styria.

The Koralm tunnel is being built in three construction stages. The third and last construction stage KAT3 extends over a length of around 12 km and will be driven in the north tunnel, for the most part with a tunnel boring machine. The Koralm tunnel crosses the massive Koralpe mountain range with a maximum overburden of about 1,200 m. The two tunnels run with a centre distance of around 40 m and are connected to each other every 500 m by cross-sections. Due to the project length at the KAT3 construction stage of about 11 km, it was necessary to efficiently connect and evaluate the data from segment production, the tunnelling (TBM data) and the surveying work as well as the results of the geological and geotechnical monitoring.

With the support of VMT GmbH and its products, the machine and survey data could be collected and merged.

Furthermore, in geologically challenging areas, the RCMS convergence measurement system was able to produce a condensed record of the ring convergences, which was also linked to the existing survey data from the tunnelling.

Project advantages

  • Thanks to good cooperation between an experienced customer and experienced service experts from VMT, the challenging drive was masterfully executed through to the final breakthrough
  • Due to the long construction period of about 5 years, it was periodically necessary to overhaul the systems used or to adapt them to changing specifications. The employees of VMT GmbH always completed this task to the utmost satisfaction
  • Thanks to VMT’s service support, all the client’s key requirements were met and the tunnelling work was completed successfully”


At a Glance Fact Sheet:

Project Name or Designation/Timescale Koralmtunnel KAT3
Location St. Paul im Lavanttal, Austria
Project requirement
Rail tunnel
Technique LDT – EPB/Hard Rock Multi-mode TBM
Diameter/Length/Bend Radius D= 9.940 mm, L= 10,474 m, R=3,000 m
VMT System utilised TUnIS Navigation TBMLaser

TUnIS Navigation Office

TUnIS Ring Sequencing

SLuM Ultra


Challenges The long duration of the project – extending over 5 years – required periodic overhaul and maintenance of the VMT systems and adaptation to changing project specifications.