A great view on history. © HOCHTIEF CZ

The mega puzzle

Hardly any transportation route in Czechia attracts as much attention as the Negrelli Viaduct, one of the oldest transport engineering projects in the capital Prague. HOCHTIEF is currently reconstructing the technical heritage site. The trick here is to create something new while preserving the old—a real-life 3D puzzle.

wss/mmdb - assetID : 171532 Linda Černá Vydrová; ©HOCHTIEF CZ

Every detail counts if you want to preserve a historic structure and make it fit for the future. Nobody knows this better than Linda Cerná Vydrová. So stones pile up at the foot of the viaduct whose 87 arches make one think of similar structures in ancient Rome. Each of these stones bears a number, as this is the only way to bring together again what belongs together. Some of the arches are so badly damaged that they have to be disassembled . “When putting together the arches to the original form, we want to use reclaimed material to the maximum extent possible,” says Linda Cerná Vydrová, the specialist who is in charge of renewal of the bridge at HOCHTIEF in Czechia. Her goal for the 3D puzzle: “We want to do the reconstruction as efficiently and professionally as possible.”

The reconstruction is carried out on almost 1.5 kilometers and 3.3 kilometers of rails will be replaced. The superstructure including technology will be completely renewed. The foundation and subsoil have to be grouted, jet-grouted and micropiled . The teams will reconstruct 100 brick, sandstone or granite arches, eight of which cross the Vltava River. More than a dozen arches will have to be completely replaced.

Looking at the Negrelli Viaduct, Linda Cerná Vydrová is full of praise: “It is unbelievable how perfectly our ancestors designed the viaduct. When it was opened to traffic more than 160 years ago, the trains did not weigh more than a couple of dozens of tons, but with the current loads and density of traffic we can see that the viaduct has lasted in extremely good shape.”

“Reconstruction will improve the technical condition of the bridge structures and the outdated mechanical signaling system will be replaced by a modern electronic system. This will enhance traffic safety even more,” Linda Cerná Vydrová lines out some aspects of the project she manages. 160 years ago, the bridge led through open, undeveloped landscape—today, it is located centrally in the capital. The local residents will feel a significant improvement as well. Anti-vibration mats and up-to-date switches are to reduce noise when rail traffic will be resumed in 2020. In future, it is planned to use the arches for cultural and social events. “And the train passengers will undoubtedly appreciate the new superstructure, which will make their travels calmer and smoother,” Linda Cerná Vydrová describes the project’s benefits.

History of the Negrelli Viaduct
The viaduct was named after its designer, Austrian engineer Alois Negrelli. The first railway bridge over the Vltava River was built from 1846 to 1849 and opened to traffic on June 1, 1850. At that time, up to 3,000 workers were on the construction site. Once completed, the viaduct had 87 stone arches: 8 of granite and 79 of sandstone. It still connects the Masaryk railway station with the Prague district of Bubny on the opposite side of the Vltava River. In 1873, it was extended by an additional 351 meters and 26 arches (10 of stone and 16 of brick) and a branch was thus created. The Negrelli Viaduct is, after the well-known Charles Bridge, the second oldest bridge in Prague and until 1910 even was the longest bridge in Europe with its length of 1,110 meters.

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