The second railway line, Divača–Koper, runs through one of the most geologically challenging areas in Slovenia. A new video illustrates the scale of the project and provides an insight into the technical challenges and the engineering solutions that have made construction possible under complex karst conditions.
Tunnel construction under exceptional geological conditions
The 27-kilometre-long Divača–Koper double-track line is one of Slovenia’s most significant infrastructure projects. More than 37 kilometres of tunnel bore, spread across seven tunnels, run through a tectonically complex karst region featuring underground caves, shafts and water-bearing passages.
Unexpected challenges in the karst
Despite extensive preliminary geological surveys, many karst formations could only be identified whilst the tunnel was being driven. A total of 93 karst formations were documented. Whilst most of these could be secured using relatively simple measures, cave systems 66 and 80 presented the project team with particular challenges.
Bespoke engineering solutions for karst terrain
Working alongside the teams from Vienna and Salzburg, ELEA iC developed bespoke technical solutions for these areas. At the heart of the project are four underground reinforced concrete arch structures that span the caves and provide a permanently secure foundation for future rail operations.
With a span of 45 metres, the largest of these underground bridges is also one of the most technically challenging structures in the entire project. It was built around 250 metres below the surface in karst terrain containing numerous cavities and water-bearing passages. The construction of this structure alone took around three months.
Digital planning as a foundation
The design of the structures was based on detailed 3D models of the tunnels, supporting structures and geological strata. During tunnel excavation, these models were continuously updated with newly acquired data. This enabled the engineering teams to adapt the supporting structures precisely to the actual geological conditions.
An optical sensor system is used for the long-term monitoring of the structures; it continuously monitors the structures during operation and thus makes an important contribution to tunnel safety.
Technical insights into the project
This major project demonstrates how modern engineering, digital planning methods and close collaboration between various specialist disciplines enable innovative solutions to complex geological challenges. The video provides an insight into the technical aspects of the project and illustrates the scale of the structures, as well as the particular challenges involved in tunnelling through karst terrain.
