The crossings of karst features in the Lokev (T1) and Beka (T2) tunnels, as well as on the section of open alignment from Divača to the first tunnel, have been fully completed.
Along the Second Track route, some karst caves of such a large scale were encountered that they had to be bridged with special structures. These are underground bridges (arch structures) that will not be visible during railway operation, as they are located beneath the tunnel tube, but are essential for the stability of the railway line.
The bridging structures were required at caves 2TDK-066 and 2TDK-080 in both the main and service tubes. The longest underground bridge measured 46 metres, and all bridges were constructed in 6-kilometre-long tunnels more than 100 metres below the surface. A more complex bridging structure was also built over cave 2TDK-076 in the Lokev tunnel (T1).
Along the Second Track route between Divača and Koper, a further seven karst features were encountered in the tunnels that required bridges longer than 15 metres. Solutions for spans of up to 15 metres were included in the design documentation, while all spans longer than 15 metres required special solutions that had not been foreseen in advance.
Open section
In the so-called open section of the route, which runs in a cut, a sinkhole had to be bridged. The bridging structure over the sinkhole was designed as a reinforced concrete prestressed slab with a 31-metre span, built under both tracks. At the sinkhole location, slope reinforcement of the excavation was also carried out over a length of approximately 30 metres.
On the open section, ground improvements were also required at nine locations, as investigations showed that the soil was not sufficiently stable in certain areas. Reinforced concrete slabs up to 15 metres long were used.
