Karst phenomena have been discovered not only during tunnel construction but also along the surface section of the second-track route. Between Divača and the Lokev Tunnel (T1), the route runs through an open cut, where a sinkhole was recently encountered during excavation work. Due to geological characteristics and stability requirements, a bridge approximately 35 meters long will be needed to safely cross this underground sinkhole.
The need for an additional bridge over the karst formation stems from previous studies, which included geological surveys. These surveys showed that the ground in this section does not have sufficient bearing capacity; therefore, to ensure the stability and safety of the second-track route, it will be necessary to construct another bridge structure.
The pre-excavation in Divača, where a sinkhole was discovered, is part of an open route approximately two kilometers long. Excavations were carried out using blasting and breaking up larger rocks, as the area has a limestone substrate. The preliminary excavation is being carried out at a width that allows for the construction of both the left and right tracks. Preliminary geological surveys were conducted in the area of the right track, where work is now continuing on the preparation of the detailed design documentation (PZI), which will serve as the basis for the bridge’s construction. Surveys have not yet been conducted on the left track; once the results are available, a suitable solution for overcoming the karst phenomenon will also need to be found there.
93 karst features discovered along the second-track route
To date, 92 karst features have been discovered along the second-track route; 5 of them required more complex bridge structures. The longest underground bridge measured 46 meters in length, and all bridges were constructed more than 100 meters underground in 6-kilometer-long tunnels, which complicated the logistics of the project.
Along the route of the second track between Divača and Koper, seven additional karst features were encountered that required bridges longer than 15 meters. Solutions for spans up to 15 meters were included in the project documentation, while all spans longer than 15 meters required special solutions that had not been anticipated in advance.
