Viaducs de la Barricade et des Bergères, Highway bridge network in Aix, France

The Barricade viaduct carries the A89 motorway over the Barricade stream valley, 80 m deep, near Aix and Merlines. Its prestressed concrete box girder, 19.56 m wide, was cast in 124 segments of 3.409 m using symmetrical cantilever construction with mobile formwork. Spans measure 60.861, 109.139, 150 and 100 m, and the deck rises at 1.1 % from west to east. The Bergères viaduct stands 200 m away.

The viaduct belongs to the first 40 km section of the A89 built between Ussel Ouest (exit 23) and Le Sancy (exit 25), parallel to the RN 89, with ASF as project owner. During earthworks for pier P3 in early October 1997, open subvertical fractures were found in the gneiss of the eastern slope, forcing the foundation shafts to be deepened below the tension-crack plane. The deck was cast in 124 segments of 3.409 m using pairs of movable formwork travelling symmetrically from each pier.

The Barricade viaduct carries the A89, the first major European-purpose motorway transverse link, on its 40 km Ussel Ouest–Le Sancy section. It stands in a type II ZNIEFF natural zone, and the Bergères viaduct lies 200 m away; the Chavanon viaduct, at the Limousin–Auvergne boundary, is 2 km west.

You can view these bridges from the valley below or while driving the A89, where they are best seen from the side. Walking access is not possible since this is an active motorway.

The longest span reaches about 150 meters and required specialized studies of the ground to account for rock fractures. These geological challenges led to adaptations in foundation design that stabilized the structure.