The Grand Pont in Lausanne is not just any bridge. It is the main artery connecting the east of the Olympic city with the west. The square and the streets under the bridge lie in a valley filled in 1874, the former Valée du Flon. The second row of the bridge arches is hidden under the fill. So it was once a really big viaduct, not only in length but also in height.
The Gran Ponte is thus both the landmark and the most important east-west connection of the city. It was widened in 1891 with a steel framework, which was replaced by concrete bay windows in 1933. The latter deteriorated and no longer met the requirements of the standards. The rehabilitation of the Great Bridge was urgently needed and was carried out in 2022. As the structure is listed in the inventory of historical monuments, the rehabilitation project was accompanied by the monument protection offices of the city of Lausanne and the canton of Vaud.
It is a bridge with several masonry vaults on two levels with six vaults on the lower level and 19 vaults on the upper level. The structure has a total length of 172 m and a maximum height of 25 m above the River Flon. The project to rehabilitate the Great Bridge consists of demolishing the 1933 concrete bays and the carriageway slab and replacing them with a new slab of prestressed concrete placed over all 19 vaults. The new carriageway consists of a continuous, smooth slab supported on the existing masonry vaults and terminated with thin curbs made of an ultra-high performance fibre cement composite (CFUP). The thin CFUP kerbs terminating the carriageway slab ensure high durability: an important aspect of these parts of the structure, which are particularly sensitive because exposed to de-icing salt. The use of stainless steel fibres and stainless steel reinforcement can further increase the durability of the structure. As part of the 2022 works, the repair of the masonry of the vaults included the restoration of the soffits of the vaults and the plinths and the repair of the joints.
To carry out the repair work, the Great Bridge had to be closed for almost a year to allow the work to be carried out quickly and cost-effectively. For this purpose, diversion routes for cars were set up, as well as a special bus network for Lausanne Transport Company (TL) buses. For pedestrians, a temporary footbridge was installed over Rue Centrale to allow almost 13,000 people to pass between the two hills every day.
The modernisation of the Grand-Pont is a good example of a construction site that involves urban planning, structural, monument preservation and logistical aspects at the same time; a team effort that requires multiple skills.
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