Bridges over the Paudèze
The bridges over the Paudèze river, located in the cities of Pully and Bemont, allow motorway N09 to cross the valley formed by the river with the same name. The two structures, to traffic in 1974, were built using the balanced cantilever method. Each bridge has five spans with a maximum length of 104 m.
Many inspections and assessments showed the bad sates of the bridges. The decks have significant mid-span deflections and the box girders are heavily cracked. Important prestress losses were also measured. The deck slab cantilevers are in poor condition with spalled concrete and corroded steel reinforcement on all edges. Important levels of chloride contamination have been measured in the concrete of the abutments.
In addition, the strength of the deck is insufficient for static loading. Seismic action also creates unacceptable concentration of action effects in one pier.
Thus, the bridges must be completely rehabilitated and strengthened.
The deck slab is to be reinforced by supporting its cantilevers with struts, allowing to maintain existing steel reinforcement in the slab. The struts will be made of ultra-high-performance fiber reinforced concrete (UHPFRC) to minimise their weight. Concrete parapets are to be built on the cantilever edges. The increase in weight requires placing additional longitudinal prestressing cables and the reinforcement of girder webs with carbon fiber reinforced polymer strips. The damaged sections are to be cut out and repaired. The abutments are completely reconstructed. The waterproofing system, the overlay as well as all the service equipment will be completely replaced. Finally, the end piers are strengthened for seismic actions.
Around the foundations, the Paudèze valley has areas with active landslides. In these areas, the piers are built on foundation shafts stabilised with active anchoring and a drainage system. However, failure of some tiebacks has been observed; they are to be replaced. In addition, two retaining foundation shafts are to be constructed upstream from the piers located in the landslide area, to reduce horizontal pressures on the foundations. The observational method is used to ensure the monitoring of geotechnical interventions.Share