The foundation of the piers of a bridge in the Rhône was a particularly difficult challenge due to the currents and rapidly variable water levels, even in summer.

The choice of the suspension bridge reduced the construction to a single central pier, which also limited the disruption to navigation.

One of Seguin’s advantages in his business is the presence, near the site, of lime from Monsieur de La Farge (today the Lafarge group), in Le Teil (Ardèche), which has the very rare property of being hydraulic, that is to say allowing concretes that set and harden under water.

This use was actually known for a long time in the Rhône valley, as a regional know-how. Seguin then uses this property on a large scale, pouring concrete masses between submerged formworks.

They form the “sole” of the foundations and they are surrounded by large blocks of rock to limit the scouring effects of the current.

The reinforced concrete.

In the construction of his first Rhône bridge, Seguin faced considerable and often new, challenges.

With his collaborators, he was on the lookout for any innovative idea that could strengthen the quality of his work.

To ensure the stability of the three gantries supporting the cables, which he feared would crack under the repeated tension of the cables, he included large vertical iron rods within the concrete of the « straight legs », which he wedged at their ends by sealed stones.

These metal bars can be stressed in tension while the concrete resists through its compressive qualities. It is “reinforced concrete”, almost 25 years before the first patent was filed on this material !

But this is a “manufacturing secret” that only the site archives reveal, and not the printed texts of the time.