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Koralm Tunnel (KAT3) stabilized by pipe umbrella system with innovative squeezed connection

The Koralm Tunnel in Austria is the core part of the Baltic-Adriatic Corridor, a planned railway link between the cities of Gdansk in Poland and Ravenna in Italy. Once completed, the tunnel will have a length of 32.9 km and cross the Koralpe Massif at a depth of up to 1,200 m. The center distance between the two parallel, single-track tunnel tubes measures approx. 40 m, and the tubes are connected via crossways every 500 m.

12 km of the double-tube tunnel are advanced from the western portal in the Lavant Valley in Carinthia towards the East – the northern tube is primarily advanced by a Tunnel Boring Machine (TBM), and the southern tube is being excavated using the cyclical method.

First, the existing Paiersdorf exploratory tunnel has been widened over a length of 7.6 km. DSI Austria had already supplied high quality ground support products that stabilized advancement during the construction of the exploratory tunnel. The northern tube has been excavated using a TBM over a 2.6 km long section. At the western portal in Carinthia, which is located in alternating layers of claystone and sand stone, the northern tube only has a minimal cover.

Protection of tunnel advancement by 15 m long pipe umbrellas

For protecting the tunnel advancement, 15 m long, Type AT – 114 Pipe Umbrellas with a tube wall thickness of 6.3 mm are used in this area. DSI Austria supplied the AT-Pipe Umbrella System in individual lengths of 3 m together with hardened solid drill bits, an AT – 114 Starter Unit and additional system accessories. The pipe umbrella system was installed using conventional drilling equipment.

To connect individual tubes, DSI Austria's newly developed squeezed connection system is used instead of conventional threaded couplers. In this method, a tapered end is inserted into the already installed tube, and both tubes are force-fitted within a few seconds using a hydraulic jack. The squeezed connection is more robust than the conventional threaded coupling and permits a faster connection of the individual pipe umbrella tubes. Furthermore, the elastic load bearing capacity of the connection is approximately twice as high as that of the threaded coupling.

Other than the AT-Pipe Umbrella System, DSI Austria also supplied 25 mm Ø, 3, 4 and 6 m long SN Anchors with ultimate tensile loads of 260 kN including accessories. Additionally, R32-250 and R38-500 Ø, 2, 3, 4 and 6 m long DYWI® Drill Hollow Bars are used as self-drilling anchors to stabilize tunnel advancement. The ground support products produced and supplied by DSI Austria also include 51 x 3,2 mm Ø, 3 and 4 m long POWER SET Self-Drilling Anchors; 51 mm Ø self-drilling spiles; 38 x 4 mm Ø steel tube spiles and Types 50/20/30, 70/20/30 and 95/25/36 PANTEX Lattice Girders.


Sankt Andrä, Carinthia, Austria, Europe - Frauental an der Laßnitz, Styria, Austria (2022)

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