The Castielertobel Viaduct[note 1] (German: Castielertobel-Viadukt) was a single track railway bridge spanning the Castielertobelbach, and linking the municipalities of Castiel and Calfreisen, in the Canton of Graubünden, Switzerland.

The replacement is a single span steel construction designed to shorten by up to 1.5 metres (4 ft 11 in) over the predicted 100 year life of the bridge.

Due to the difficult geological conditions in the Schanfigg valley, a total of 18 tunnels and 40 bridges needed to be created between 1912 and 1914 for the privately built Arosa line.

However, the special site conditions dictated the inclusion of stampfbeton (unreinforced concrete compressed by stamping) in the cores of the stone pillars.

By contrast, a potential rock fall at the uphill portal of the Bärenfalle-Tunnel threatened to block passage through the tunnel just at the moment when transport of machinery to the Lüen power station was due to begin.

The site conditions soon proved to be very unfavourable to the completed viaduct, with the result that the 53-metre (174 ft) high main pillars slipped each year by about 6 millimetres (0.24 in) downstream towards the Plessur River.

During that work, the valley side abutment was underpinned by a bell-shaped concrete block, which was clad with Hunziker stones,[clarification needed] and reinforced with rails.

Additionally, a 7-tonne (6.9-long-ton; 7.7-short-ton) counterweight suspended from a wire rope provided a 50-tonne (49-long-ton; 55-short-ton) pulling effect on the pier heads, along the line of the railway formation towards Chur.