Drivers on section 8 of the A89 motorway cross the Sioule Valley on a viaduct 991 m long and 150 m above the river.
The Sioule Viaduct has 8 spans of different lengths: 49 m, 98 m, 157.50 m, 192.5 m, 192.5 m, 150.50 m, 98 m and 52.5 m.
The deck is a single-box girder bridge with 19.5 m wide twin webs, built using the successive corbelling method on a form traveler.
Three balanced cantilevers with 2 x 25 segments are 190 m long and of variable height (10 m on piers and 5.5 m at mid-span). They are embedded into three large double-shafted piers (P3, P4 and P5), respectively 82 m, 120 and 135 m high.
The four balanced cantilevers of the side spans (1-2 and 7-8) are of constant height (5.5 m) and have a maximum length of 120 m. The single-shafted lateral piers bear the deck by sliding bearing systems and have transversal seismic stops.
The viaduct is built on wide shafts: four 5 m shafts for the large piers and a single 7 m shaft for piers 2 and 6. The smallest piers (1 and 7) are on shallow-strip foundations. The piers are set in B50 concrete and the deck is built in B70 G silica fume concrete.
The 31T15 cables of external prestressing were injected with petroleum wax to allow them to be removed.
Throughout construction, the environment and the preservation of the Sioule Valley were primary concerns for the contractor and contractor assistant.