Brusio spiral viaduct, Brusio, Bernina district, Graubünden canton, Switzerland

Brusio spiral viaduct
Brusio spiral viaduct Viadotto elicoidale di Brusio The Bernina Express on the viaduct

The Brusio spiral viaduct (or Brusio circular viaduct; Italian: Viadotto elicoidale di Brusio, German: Kreisviadukt Brusio) is a single-track nine-arched stone spiral railway viaduct.
A signature structure of the World Heritage-listed Bernina railway, it is located near Brusio, in the Canton of Graubünden, Switzerland, and was built to limit the railway's gradient at that location within its specified maximum
  

 The viaduct was opened on 1 July 1908, upon the opening of the Tirano–Poschiavo section of the Bernina Railway

    

 A spiral viaduct was required immediately south of Brusio to limit the railway's grade to the required maximum of 7%, so the train would not slip on the way up, or be uncontrollable on the way down. Geological factors prevented the boring of the spiral tunnel that had originally been planned. Engineers therefore decided to construct on the valley floor a 360 degree curve with a 50 to 70 m (160 to 230 ft) radius, and the viaduct forms part of that curve                                                                     



The spiral viaduct is 110 metres (360 ft) long, has a horizontal radius of curvature of 70 metres (230 ft), a longitudinal slope of 7%, and is made up of nine spans, each 10 metres (33 ft) in length.

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