As repairs rumble on under the Thionville Beauregard viaduct across the French border, officials are ready to "close the structure within the hour" in the event of major traffic-related tremors.

Beneath the heavy flow of 80,000 daily motorists on the A31, a massive engineering operation is quietly unfolding. Without most drivers even noticing, workers are pouring a concrete sarcophagus around the abutment that supports the Beauregard viaduct.

At 50 years old, the viaduct's abutment, or in other words the “foot” of the bridge, has suffered significant rust damage over time. The new concrete casing is critical to preserving its stability.

Given the delicate state of the structure, the construction site is being monitored around the clock. “We are sensitive to any possible movements of the structure, which is monitored 24 hours a day”, explains Benjamin Collin, deputy head of the Interdepartmental Directorate of East Roads (DIR Est).

The corroded scales encircling the abutment wall are dotted with 250 automatic control points that constantly monitor the structure for movement. This is why motorists have been required to drive at 70 km/h on the Beauregard viaduct since May and why site managers are taking a step-by-step approach to the work. "We would rather everyone slow down both above and below than have to close the viaduct", says Benjamin Collin.

‘DIR Est will not take any risks’ 

This is the big risk: "The faster we drive, the more we will cause the bridge to vibrate", warns Sébastien Delbirani, head of the Engineering Structures Department at DIR Est. Increased vibrations on the bridge risks "aggravating the problem, and therefore runs the risk of having to close the bridge."

The head of the Engineering Structures Department at DIR Est is very clear: "Yes, there is a risk of having to close it. If the abutment presents a major risk that will compromise its structure and the structure of the bridge, the DIR East will take no risks and we will close the structure." Because, he says, "there is no room for improvisation on a structure like the Beauregard."

In practical terms, if the structure's automatic detection systems reach the alert level, "we will be able to close the structure within an hour of the alert", says Sébastien Delbirani. The closure scenario and procedure, which RTL Infos has been able to consult, are on the table and are being discussed with the Moselle Prefect.

‘The closure could last several months’

In the event of a closure, which is vital for traffic on the A31 and for cross-border commuters in the Moselle region, motorists travelling from Metz to Luxembourg will be directed to remain on the A30, then rejoin Thionville via interchange 43 before merging back onto the A31. The same applies in the opposite direction.

During this time, the bridge will be empty and experts from the DIR Est will be able to carry out various assessments; either to lift the alert if there is no danger, or to carry out immediate consolidation work before the situation worsens.

In the worst-case scenario, "the closure could last several months, or even longer, if the movements become too much of a risk, the structure of the bridge is compromised and truly represents an irreversible problem", explains Sébastien Delbirani.