Today marks exactly 20 years since the opening of Slovenia's longest viaduct, Črni Kal, on the A1 motorway corridor between Koper and Šentilj, Slovenia. This also finally established a direct highway connection between Ljubljana and Koper.The Črni Kal viaduct is the largest and longest bridge structure in Slovenia. With five steps in a horizontal radius of 800 meters, it spans the Osapska Valley, with the highway descending from an elevation of 420 meters over the Karst Edge down to the coast.
The viaduct is characterized by its extraordinary length of 1,065 meters and a height exceeding 100 meters, extreme weather conditions, especially strong bora and southerly winds, construction in a geologically sensitive area, and the impact of the project on the landscape.
The substructure of the viaduct consists of two abutments and eleven piers, five of which are double piers, while the remaining six are tall single piers that split into a Y-shape at the top. The maximum height of the piers reaches 95 meters. The piers are deeply founded on wells up to 24 meters deep.
In planning the placement of the viaduct into the environment, various options were explored to adapt the engineering structure to the natural surroundings – both the arrangement of the piers and the proportions between the height of the piers and the spans of the superstructure harmonize with the various landscape conditions.
The arrangement of the middle, tallest piers, which are aligned with the natural relief’s terraces, significantly contributes to the harmonious appearance of the viaduct. With a consistent concept of landscape integration, structural solutions, and construction technologies, the viaduct recreates the natural closure of the valley and has become a new spatial feature that changes, yet complements, the landscape.
The authors of the first-prize-winning design competition, dr.h.c. Marjan Pipenbaher, MSCE and prof. Janez Koželj, MSArch, received numerous national and international awards in the fields of engineering and architecture. Main designer: dr.h.c. Marjan Pipenbaher, MSCE.
Project details:
Črni Kal Viaduct
