Many and long known reasons

“We only shed light on these issues when tragedy strikes,” lamented Mélissa Menet, Martine Aubri’s chief of staff, after two buildings collapsed in Lille on November 12, killing the 45-year-old doctor. . Since that day, the city’s health inspectors have been inundated with calls and reports of disturbances in the buildings have multiplied. But there is nothing new under the sun. The probable causes of the tragedy are perhaps the same that caused the cracks in the buildings of Vieux-Lille. Reasons we discover today but didn’t belong yesterday.

Since the tragedy, hardly a day has gone by without firefighters and city services evacuating buildings after reports of cracks in the facade or basement. Interventions responding to the precautionary principle applied to the letter in the face of a growing concern movement. Nevertheless, the pathologies at the origin of these disorders have not been revealed recently. “There are three recurring things for Lille, starting with the fact that the city was built entirely on clay soils without much succession or elevation,” explains Eric Tahon, a technical construction expert at the metropolis of Lille.

Relatively unstable underground

“The whole center of Lille was built on the old bed of the River Deûle, filled in, drained, canalized,” adds Jean-Yves Mereau, president of the old Lille Renaissance association. So, beneath our feet is a clay substratum resting on limestone upon which stacks of oak trees have been driven as foundations to support the buildings. “For almost fifty years, we have built underground parking lots and pumped water so that these parking lots are not flooded. In addition, there is the effect of lowering the water table, “he continues. A “famous” event that needs to be added is the event of drought that compacts the clay. Then we get a combination that results in the sinking of buildings.

However, the soil’s composition is not the only culprit. “Since the 20th century, the buildings of Vieux-Lille have been continuously modified to eventually become overused,” insists the construction expert. Where previously a single family was housed in the building, now one family is housed on each floor, increasing the load factor of the structure accordingly. “When you’re already fat, it’s not good for your knees. It’s the same for buildings,” adds Eric Tahon.

Nature does not like a vacuum

The common denominator between the collapse and the warnings that followed is the presence of shops on the ground floor. Jean-Yves Mereau notes: “Vieux-Lille also has a big problem, the fashion is to replace the load-bearing walls with beams and bring several houses together to make large commercial surfaces”. “These transformations, if they are not carried out according to the rules of art, reduce the structural points and destabilize the buildings”, confirms the expert.

The third most common cause of building pathology is lack of maintenance. Even as the president of the Renaissance du Lille ancien admits that the general condition of the building in Old Lille is “fairly good,” he also acknowledges its shortcomings. “The collapse of buildings left to decay by their owners, there are already some, rue des Arts or rue du Vieux-Faubourg,” he recalls. “The owners don’t do the job or they do it badly. Sometimes there is a lack of funds, especially for small condominiums. It even happens that we hide the problems behind plasterboards”, complains Eric Tahon.

Does the tragedy in Lille find its origin among these three causes? Our interlocutors are rightly cautious not to advance in this matter. This question can only be answered by the current forensic examination as part of the homicide investigation led by the Lille prosecutor’s office.

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