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Origin and history

The viaduct of Souzain, built between 1903 and 1905 under the direction of engineer Louis Harel de la Noë, was a mixed railway structure (rail and road) located between Saint-Brieuc and Plérin, Brittany. With a total length of 259 meters and a height of 32,60 meters, it crossed the Gouët valley. It consisted of three distinct parts: a reinforced concrete access structure, a 210-metre main viaduct with 23 masonry arches, and a 47-metre secondary structure. This project was part of the development of the rail network of the North Coasts to boost the local economy, which was marked by population decline and relative isolation.

The construction of the viaduct, led by teams led by Harel de la Noë, used innovative techniques for the time, such as reinforced concrete and counterfeit piles, significantly reducing costs. The materials, including local stones and cement imported from Dunkirk, were implemented by approximately 120 workers working under demanding conditions. Despite a fatal accident in 1904, the works were completed at the end of 1904, and the viaduct was inaugurated in June 1905. It became a symbol of technical progress, although its pioneering reinforced concrete design also caused its premature deterioration.

First used for rail transport, the viaduct was converted to exclusively road use in 1956 after the closure of the line. By the 1970s cracks had appeared on the piles, revealing the limitations of the knowledge of the period on reinforced concrete: lack of vibration and poor grain size. Despite attempts at restoration and an inscription to historical monuments in 1993, the viaduct, considered irreparable, was energized on 27 June 1995. Two batteries were preserved and are now exposed to Langueux and Saint-Ilan.

Souzain's viaduct illustrates both the technical audacity of its time and the challenges of preserving industrial heritage. Designed in a context of modernization of Breton infrastructure, it was a major witness of French engineering of the early twentieth century. Its destruction, despite its heritage inscription, raises questions about the management of aging works and the value given to technical heritage. The preserved remains today recall the legacy of Louis Harel de la Noë, pioneer of reinforced concrete art.

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