Innovative AT – Pipe Umbrella Systems used in Slovenia's Largest Construction Project, Tunnel T8

The second track between Divaca and Koper is one of Slovenia's most important infrastructure projects. Linking the seaport Koper and Divaca, the railway will have a total length of 27 km and includes eight tunnels and three bridges. The railroad will be part of the EUR TRANS European Transport Network (TEN-T) and will meet the growing demand on this essential route for Central Europe.

Slovenian authorities and the 2TDK and CPG consortium, a Slovenian-Turkish consortium consisting of Kolektor CPG (Slovenia), Yapi Merkezi Insaat, and Ozaltin Insaat, launched the project in May 2021. The consortium signed two contracts with EUR 628.3 million to construct the new tracks. In the first phase, the construction includes the rail line section from Divana to Črni Kal and the second section from Črni Kal to Koper.

The new line runs through geologically difficult terrain with an altitude difference of about 400 m. However, since the maximum gradient of 1.7% for rail traffic must not be exceeded, the route will pass through eight tunnels with a total length of 21 km and several bridges.

Starting from Koper, the consortium in charge started forepoling the southern tunnel T8. Designed as a double tube, the 3,808 m long T8 tunnel also includes the construction of cross passages and escape routes for the case of emergency evacuations.

DSI produced and supplied all the ground support equipment for this excavation, including drill steel, lattice girders, SN Anchors with 28 and 32mm, DSI Hollow Bar Anchors, 32/280, R32/400, as well as the AT – Pipe Umbrella System AT-114. Avesco AG provided several Sandvik Jumbos, type DT 922i, for mechanical excavation and blasting with pre-installed AT – Pipe Umbrella Automation Units with squeeze connection system developed and patented by DSI. The pipe umbrellas were installed with a range of 15m, whereas each 3m tube is force-fitted with the squeezed connection developed by DSI. In this method, the tapered end is inserted into the already installed tube, and both pipes are force-locked within a few seconds using a hydraulic press. Additionally, the supplied AT – Casing System strengthens the crown and improves the load-bearing capacity.

DSI is proud to produce and supply high-quality propping and forepoling equipment for this significant project in Slovenia. The completion and commissioning of this project are scheduled for 2026.


2TDK d.o.o, Ljubljana, Slovenia


Kolektor CPG (Slovenia), Yapi Merkezi Insaat, and Ozaltin Insaat

DSI Unit: 

DSI Underground Austria GmbH

DSI Underground Scope:

Production, supply, technical support

DSI Underground Products:

AT – 114 Pipe Umbrella System; DSI MAI® Pump; drill bits; lattice girders; SN Anchors ⌀28mm, ⌀32mm; DSI Hollow Bar System, 32/280, R32/400


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