On Monday, 7 April 2025, a report was broadcast in the Second Morning Chronicle on Val 202, in which Damir Josipovič, a member of the Project Council for Civil Oversight of the implementation of the Divača–Koper second railway track project, stated that karst features along the route of the second track were being backfilled, thereby preventing water flow.
Below we publish the full appeal by Dr Mitja Prelovšek from the Karst Research Institute, addressed to Mr Josipovič. Mr Josipovič did not respond to Dr Prelovšek’s appeal, in which he was asked to substantiate his claims with evidence.
Dear Sir,
In recent days, you have publicly expressed concern regarding the backfilling of water caves along the 2TDK route and the resulting practical obstruction of water flow. Your statements, also due to the transparency and public attention you achieve as a member of the Project Council for Civil Oversight, are concerning, as such practices should not occur. In order to prevent precisely the issues you are warning about, several measures were adopted and implemented for the construction of 2TDK, including:
development of cave-bridging measures during the construction planning phase,
hydrological monitoring, in addition to mandatory monitoring, including supplementary monitoring (the Beka–Ocizla cave system),
securing financial resources for cave-bridging measures,
anticipating multi-day work stoppages upon the discovery, exploration, and bridging of caves, including temporary relocation of worksites,
signing of the Protocol on Procedures in the Event of Cave Discoveries,
mandatory notification of karst supervision authorities by contractors regarding every discovered cave,
regular weekly karst supervision of all construction sites, particularly excavation faces in tunnels T1 and T2,
speleological exploration and surveying of caves, including karstological assessment of the cave’s hydrological function,
preparation of hydrological bridging plans coordinated between karstologists, designers, and geotechnical engineers (e.g. deepening excavations to the water flow level, installation of piping connections, creation of channels along the outer side of the concrete lining),
implementation of hydrotechnical measures during cave bridging,
supervision of cave-bridging implementation by karst oversight authorities.
Backfilling as a final cave-bridging measure was carried out only exceptionally, since the general environmental protection objective was the preservation of all cave sections outside the excavation zone, while even within excavation areas measures were implemented to protect cave inventory and features. Cave backfilling was carried out only under the following conditions:
when no other practically feasible and safe method of bridging the cave was available,
when the backfilling had virtually no impact on water flow.
Already due to the first condition, a relatively small number of caves were backfilled, as such a measure represented an exception rather than the rule, even if the hydrological characteristics of the caves were entirely disregarded. In none of the 90 newly discovered caves did we encounter cave passages showing signs of prior backfilling before exploration, which demonstrates the diligence of excavation contractors in reporting cave discoveries and indicates a minimal possibility of undocumented water caves being backfilled. To my knowledge, neither the contracting authority, the investor, nor the contractors were involved in decision-making regarding hydrological cave bridging, nor did they attempt in any case to influence professionally agreed hydrological bridging methods — even when this resulted in undesirable delays and increased costs. Backfilling water caves would also create negative technical consequences for the tunnel itself, such as increased hydrostatic pressure, cracking of concrete linings, and warranty claims, and I therefore do not believe this would be in anyone’s interest.
In areas where the tunnel intersected with permanently or periodically water-bearing caves, the tunnel was constructed in a non-drained design despite all hydrotechnical measures, including reprofiling of the excavation profile whenever this later proved necessary. This prevented excessive inflow of water through the porous outer concrete lining into the tunnel drainage pipes, along with significant drainage of the aquifer and overloading of the tunnel water drainage capacity. The thicker concrete lining in non-drained sections ensured the tunnel’s long-term stability.
More extensive technical hydrological bridging measures were implemented in the following water caves, where (epi)phreatic water flows were identified, even if only occasional:
2TDK-080 (deepening of excavation to the level of the water flow within the cave, installation and concreting of a hydrological bypass pipe, separation of the preserved cave section with blind formwork),
2TDK-063 and 2TDK-065 (drilling a dense phalanx of forepoles sideways through the cave entrance below excavation level, installation of reinforcement mesh and geotextile to prevent backfill material from entering the cave, followed only then by continuation of excavation),
2TDK-024, 2TDK-041 and 2TDK-044 (cutting channels for hydrological bypasses along the outer concrete tunnel lining),
2TDK-042 (temporary bridging of the entrance with a reinforced concrete slab, stepwise excavation approach from both tunnel excavation directions, implementation of final bridging without backfilling).
For smaller quantities of water, limited to vadose rather than phreatic flow, additional pathways were preserved along the outer concrete lining in several caves (through preserved cave sections, carved channels, or piping installations).
To the best of my knowledge (inspection and exploration of more than 90% of the caves, preparation, coordination, and supervision of bridging measures for virtually all 90 newly discovered caves), the backfilling of water caves with obstruction of water flow did not occur. I am proud of this fact and mention it at practically every public lecture on the caves along the 2TDK route, of which there have been many in recent years (Klanec pri Kozini, Divača, Postojna, Ljubljana). However, I do not recall seeing you at any of them, which would have demonstrated a clear interest in the topic and would have made this explanation unnecessary.
Your media statements therefore surprise me, and as a representative of karst supervision I call upon you to provide me (and, with regard to cave bridging, also the other persons copied in this message) with a list of water caves where, to your knowledge, backfilling occurred, so that I may obtain information from other supervisory bodies and objectively inform the media about the methods used for hydrological cave bridging.