Chillon Viaducts

Structural studies on the bridge bearing capacity showed that the main failure mode at Ultimate Limit State (ULS) is punching of wheel loads of heavy trucks through the 18 cm thin deck slab, though structural safety requirements currently can be fulfilled. Further investigations revealed that the concrete is prone to alkali aggregate reaction (AAR) due to its proximity to the Lake of Geneva. These assessments lead to the conclusion that the deck slab should expect a significant concrete strength reduction in the future, with an associated reduction in punching shear resistance. As the replacement of the waterproofing on the deck slabs was planned for 2014-2015, its combination with a strengthening intervention was investigated. Several options have been studied but none were fulfilling all the structure constraints: conventional concrete overlay was too thick with a lower durability, metallic structure was difficult to install because of the confined workspace of a box girder and did not offer a shield against environmental threats.

The final study has been decided to consolidate the viaduct by adding, on the previously hydro-jetted top surfaces of deck slabs, a 40 to 50 mm thin layer of Ultra High Performance Fibre Reinforced Concrete (UHPC) which is additionally reinforced by steel rebars, on the top surface of the deck slab.

This project is one of the biggest overlay project in the world right now, with industrial quantities of Ductal® cast per day (up to 80 m3), over several weeks (6 in 2014 and 5 in 2015) to reinforce a twin 2.1 km long highway viaduct on a 53000 m² deck slab. Exceptional execution methods developed for this project have demonstrated the efficiency of the reinforced UHPC strengthening solution. The strength of the established formula has reduced the risks during the construction, particularly the workability of UHPC with the summertime temperature. Combination of UHPC with rebars offers an efficient way to produce highly durable reinforced UHPC tensile membranes to reinforce existing structures.

This intervention also improved the overall structural capacity of the bridge which allowed the increase in traffic +10% in 3 years, over 50,000 vehicles per day.