A new landmark for Aarau

In the Swiss town of Aarau, a 70-year-old bridge is giving way to the "Pont Neuf" - the new building stands out for its unusual architecture and elaborate exposed concrete surface and is of great importance to the town, the canton and the local population. Implenia Construction Manager Dominik Sieber looks back on the project.

The Pont Neuf project

Traffic rolls over the new chain bridge, pedestrians also cross it - the new construction with the project title "Pont Neuf" bridges the Aare and connects Aarau's old town with the Scheibenschachen district, from where neighboring communities such as Erlinsbach and Küttigen are reached via main roads. After two years of construction, the new Aare bridge was opened to single-lane traffic in September, and the second lane was also open to traffic from the end of October.

This article by Petra Stocker appeared in its original form on the blog of the Swiss Association of Master Builders.

The bridge is open, but the construction project is not yet complete. By summer 2023, construction foreman Dominik Sieber and the team from ARGE Kettenbrücke (Implenia, Rothpletz, Lienhard + Cie AG, Meier + Jäggi AG) will dismantle the auxiliary bridge they built in 2019. There, they will also build further retaining walls along the Aare and finally turn their attention to the environmental work. A bike path under the bridge along the Aare is also still to follow. "There is still a lot to do," says Dominik Sieber.

The bridge in numbers:

6500 cubic concrete
1400 t of reinforcing steel
visible formwork 6000^m2
then again about 5000^{m2 of} normal formwork
connections: Screw reinforcements 1200 sleeves

falsework (underneath) approx. 1300 t steel
900 m bored piles
length 120 m, width 17 m (parapet to parapet), lane width 9 m
2 lanes
2 sidewalks

The auxiliary bridge allowed traffic to be diverted while the ARGE team dismantled the existing bridge, built in 1949. "The bridge was showing signs of age," says Dominik Sieber, explaining the reason for the new construction. The construction foreman is responsible for concrete construction and deputy site manager. "I often do the operational work outside, also coordinate the subcontractors and partly also the hydraulic engineering work," he describes his job.

"I like the rather shirt-sleeved culture on the construction site."

Dominik Sieber

Sieber arrived at his current profession in a roundabout way. After graduating from high school and studying civil engineering at the ETH, he worked for five years in a planning office. Then he moved to the construction site. "I like the rather "shirt-sleeved" culture on the construction site," Sieber explains. In the engineering office, he dealt primarily with academics; on the construction site, on the other hand, you encounter the whole society, from the subcontractor to the client. This was also the case with the "Pont Neuf" project. At peak times, 20 people from ARGE were on the site, including many bricklayers and formworkers, foremen and road builders. In addition, there were various subcontractors.

The name of the bridge is based on the famous model in Paris. There are also visual similarities. "This one is more modern and curved, but still a massive structure," says Dominik Sieber. The new bridge is expected to last 100 years. Certain parts will certainly need to be replaced by then. "But one builds bridges today with foresight. In such a way that you can easily get to the relevant places and replace the 'wearing parts'."

A bridge with color

The Chain Bridge has its own "look" and stands out: Nothing on the bridge is vertical, everything is round or crooked. The exposed concrete was colored at the factory in a friendly yellow-brown-gray shade and given a board structure, making the surface resemble rustic wood. This effect was achieved using a special formwork method. "It was quite complex," says Dominik Sieber. The concreting process of the colored concrete was standard, but a greater challenge was to color a cosmetic mortar for closing the binding points so that it had the same color as the concrete.

Although the bridge crosses the Aare, the construction workers sometimes got a little wet. "In order to dismantle the old bridge piers and build new ones, you use so-called sheet pile boxes made of steel profiles - they are like an inverted bathtub," Dominik Sieber explains the construction process. The water was pumped out, allowing the construction workers to work in the dry. "At peak times, however, we had to pump out up to 40,000 liters per minute," recalls the construction foreman.

Although the bridge crosses the Aare River, the construction workers sometimes got a little wet: to demolish the old bridge piers and build new ones, they use so-called sheet pile boxes made of steel sections - they are like an inverted bathtub.

Construction site with audience

Dominik Sieber is satisfied with the result. "It has become really beautiful," he says. The construction site is located in the middle of the city and is therefore under direct observation by the public. During the construction phase, the auxiliary bridge was the ideal visitor balcony for the construction site," says Dominik Sieber. "During the Corona period, it was a popular vantage point for walkers."

"During the Corona period, the auxiliary bridge was the ideal visitor balcony for the construction site and a popular vantage point for walkers."

Dominik Sieber

The population also seems to be satisfied with the structure. "The vast majority of feedback is very positive." Dominik Sieber is sure that the auxiliary bridge contributed to the acceptance of the new bridge construction site: "Thanks to it, there was no traffic chaos."

The construction foreman first rode over the bridge on his bicycle. A special moment. Then, when the public was allowed to drive on the bridge for the first time, he observed people's reactions. "I often saw joy in their faces," he says. Some people took out their cell phones and filmed the ride.

A bridge that connects

A bridge is always a connection between two places and therefore very valuable for the public. That makes him proud, says Dominik Sieber. He knows that this bridge will outlive him, a structure that will remain - and shape the region, far beyond the city limits.