KAT2 Koralm tunnel

Underground Mining Traffic tunnel construction

twin-tube railway tunnel

Project data

ÖBB Infrastruktur AG
Building Method
continuous drive
Burst volume
ca. 4 Mio. m³
Order sum
570.0 million EUR (as part of a consortium)
Period of implementation
January 2011 - January 2019
Diameter / Cross-section
77 m²

Sekretariat Untertagebau
+43 5556 7181-817

The Koralm tunnel forms the central section of the twin-track high-speed "Koralmbahn Graz - Klagenfurt" railway line and connects the federal states of Styria and Carinthia. It is located on the Pontebbana axis, which, as the main link between the Baltic and Adriatic Seas, represents a central project of Austrian infrastructure development.

The 32.8-km tunnel is divided into three stages, of which construction lot KAT2, at approximately 19 km in length, is the longest section. The two single-track main tubes (excavation area of approx. 82 m²) are connected by cross-passages at intervals of 500 m. The construction of an emergency stopping area of over 900 m in length in the central part of the tunnel also forms part of the construction contract.

A further special feature of the KAT2 lot that needs to be mentioned is access to the two tunnel tubes. This will be accomplished by means of a 60-m-deep shaft to be built specifically for the implementation of the underground work. It is estimated that the planned construction measures will take 8 years. After the first construction phase in 2011/2012, during which the two tubes of the shaft were excavated in both directions (to Graz/East and to Klagenfurt/West) using cyclic excavation methods (northern tube 2.2 km/southern tube 2.8 km), the mechanical excavation work using tunnel boring machines for the remaining stretch (northern tube 15.6 km/southern tube 17.1 km) commenced. On 29.01.2013, tunnel sponsor Ms Margit Fischer switched on the first tunnel boring machine for the main construction lot KAT2. Until 2016, two 10-m double-shield TBMs will excavate 17.1 km and 15.6 km respectively of the two parallel tunnel tubes at the heart of the approx. 33-km Koralm tunnel. The completion of the structural measures is scheduled for 2019.


After more than 17 km of tunnelling, the breakthrough successfully took place at around noon on 14 August 2018, 1,200 metres below ground level in the southern tube of the Koralm tunnel. The project has thus far taken 15 years; now, just under six kilometres remain to be excavated in the northern tube.


Tunnel boring machine Mole 1 has covered exactly 17,127 metres from its starting point in Leibenfeld in Styria. According to the ÖBB, this represents a world record for a TBM. The second Styrian boring machine in the northern tube completed its work back in February. The TBM known as Kora, which set out from Carinthia in 2015, has just under six kilometres to go. In total, around 800 people are working on the construction of the sixth-longest railway tunnel in the world.


The target date for the overall commissioning of the Koralm railway is December 2025. It will then be possible to get from Graz Klagenfurt in around 45 minutes. (APA)

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