The GCT1 and SCT1 Tunnels on the Second Railway Track of the Divača-Koper Railway

 

Investor: DŽI, Direkcija za Železniško Infrastrukturo 

Phase: building permit obtainment, tender obtainment

Client: SŽ - Projektivno podjetje Ljubljana d. d. 

Issuing of proj.doc.: July 2011 

Project designer: dr. Vojkan Jovičić, BCE

Project leader: dr. Vojkan Jovičić, BCE

Project no.: ic 50/10-G/1 

Inv. value: 121.000.000 € 

Contract value: 770.000 € 

T1 Tunnel

T1 Tunnel

Project description

The existing Divača-Koper railway line runs on topographically very unfavourable terrain and represents a bottleneck in the Slovenian railway network due to its high inclinations. Studies have shown that the single-track, electrified Divača-Prešnica-Koper line will no longer be sufficient in the near future due to the increasing traffic of the port of Koper and have justified the need to build a second track from Divača to Koper.

The Divača-Koper line is part of the Pan-European Corridor V, which is fully included among the EU's priority transport projects. In April 2005, the Government of the Republic of Slovenia adopted the Regulation on the National Location Plan (hereinafter: NLP) for the second track of the railway line on the Divača-Koper section. The route of the new line is planned in such a way as to allow the connection of the Trieste-Divaca railway line.

The T1 and SCT1 tunnels are planned as part of the single-track railway link Divača-Koper on the section Divača - Črni Kal.

Tehnical features

The tunnel comprises the main tunnel tube GCT1 with a length of 6,726.8 m and the parallel service tunnel tube SCT1 with a length of 6,683.1 m. The two tunnel tubes are interconnected via thirteen crosspassages, with a total length of approximately 325 m. The design documentation covers approximately half of the tunnel, namely between the stations km 6+329.00 (limit of treatment) and km 9+679.3 m, including the southern portal of the tunnel. The total length to be treated is 6683.2 m, of which the GCT1 main tube is treated at a length 3363.1 m and the SCT1 service tube for 3320.1 m.

The geological conditions in the route of the main and service tubes are very similar. The lithology along both tubes is identical and the fault structures are identical in both tubes. The general orientation of the main structures runs quite transversely along the route, intersecting the two tubes in roughly the same locations. 77 % of the southern half of the tunnel passes through Karstified limestones of Upper Cretaceous and Palaeocene age, which are fractured, but tectonically largely undisturbed; they are intersected only by a more prominent fault here and there in the route of the tunnel. From km 9.0 onwards, the route passes into the flysch strata; there, the southern portal is located.

The area of potential karstification occurs in 90% of the tunnel route, where it passes through limestones. The T1 tunnel passes through an area of highly developed karst, where 177 karst caves have been registered. From the surveys carried out so far, it is known that the planned route of the second railway track in the area of the T1 tunnel (from the chainage at km 2+979 to the chainage at approximately km 9+679) will pass through hydrogeologically challenging territory, both in terms of the construction itself as well as the impact on the environment. Accordingly, the design solutions have been envisioned so that the tunnel is partially completely watertight or at least has no impact on the underground hydrogeological systems.

Participating designers and project organisations

  • SŽ-PP d.o.o. - lead partner

  • Lineal d.o.o. - access roads and preparatory works

  • Ponting d.o.o. - viaducts

  • Elea iC d.o.o. - tunnels

 
Construction, Underground structuresPetra Bukovinski