Koralm Tunnel – giant Cutterhead, precise Bolting

One of the world’s longest tunnels is being produced: the Koralm Tunnel in the south-east of Austria will link Styria and Kärnten and reduce the travel time between Graz and Klagenfurt from 3 hours to one. The roughly 33 km long core section of the Koralm Railway is due to be completed in 2022. Then the tunnel penetrating the Koralpe will become an integrated part of the high-speed rail link, connecting Poland, the Czech Republic, Slovakia, Austria and Italy with each other. After work is finished as scheduled in 2016, it will be one of the world’s longest rail tunnels: only the Chunnel and the Gotthard Base Tunnel will actually be longer.

An 180 m long tunnelling machine is eating its way through the rock. 80 individual bits in the roughly 100 t heavy cutterhead cater for a daily rate of advance of between 25 and 30 m, on more than 240 days per year. The service specialists exclusively use Hytorc hydraulic wrenches to ensure that the gigantic tunnel boring machine can operate perfectly.

A special team belonging to the Kat2 JV – consisting of Strabag AG and Jäger Bau GmbH – is responsible for maintenance. This maintenance shift must for instance change the bits on a regular basis. On average a bit is changed after a 5 m round of advance. According to foreman Walter Pacher nothing is more suitable for this purpose than Hytorc hydraulic wrenches. These tools were first used to set up the site after firms responsible for assembly brought them along with them and they served the purpose really well. In the interim Hytorc tools have become standard for erecting the site on the basis of the good experience made with them.

Wrenches such as the Hytorc Avanti are applied. This multifunctional torque tensioner is compact and ideal for classical calibrated, torque controlled bolting of standard nuts with reaction arm, inline-rails or special arms. If so desired the tool can also function without reaction arms and counteracting wrench with the aid of a Hytorc DISC.

The Aker Wirth GmbH estimates 45 minutes for changing the bits it produces. The Koralm project’s ambitious team in some cases accomplished the job in 20 minutes thanks to these clever tools – without violating the corresponding regulations. Pacher went on to say that “our rough working environment calls for stable, durable as well as handy tools”, adding “furthermore, the work has to be accomplished quickly and safely extremely precisely for torque. The Hytorc tools fulfil these requirements reliably”. Work at the cutterhead must be carried out with particular precision as any contamination while assembling a bit can result in the individual bit coming loose so that the whole machine consequently comes to a standstill. However Hytorc hydraulic wrenches are in use elsewhere as well: In fact, all major bolting connections on the cutter are assembled hydraulically”, says Goliasch, a mechanical engineer, who is responsible for all the machines, installations and tools functioning perfectly in the team.

The Koralm Tunnel is designed for speeds of up to 250 km/h. The tunnel will be built over a distance of some 12 km in keeping with the “New Austrian Tunnelling Method”, which has been customary since it was introduced during the 1950s, which takes advantage of the rock’s ability to sustain itself. The sections driven by tunnel boring machines will be secured by more than 17,000 concrete rings, each weighing around 47 t. The tunnel’s internal radius amounts to just under 4.4 m after it has been lined. Never before have drives of such a length been produced with this diameter anywhere in the world. The best achieved so far was 12 km. In the case of the Koralm project, the 2 bores will amount to 14 and 17 km respectively.


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