In Paris, career collapses have worried the authorities since… Louis XVI.
It was he who created, in 1777, a service responsible for listing and mapping old quarries, monitoring and consolidating the voids located under the public domain.
Even today, some 770 hectares of void still remain under the streets of the capital.
Parisians are therefore not immune.
As proof, at the end of June 2020, a 10-meter fontis formed in the cellar of a building on rue Manin, in the 19th arrondissement of Paris, making the building unstable.
“After the building was evacuated, a security perimeter was decided and we installed props,” explains Dominique Boussugue, building pathologist.
For 15 years, this expert has campaigned for the systematic carrying out of a diagnosis of the state of the structure of any building constructed above a quarry.
"The first extractions date back to Antiquity"
And there are many. "The first extractions date from Antiquity, and the first underground from the 12th century," specifies Marc Hannoyer, of the General Institute of Careers in Paris. Limestone has been used in the construction of many monuments, such as Notre-Dame. Gypsum is present in the Paris region in exceptional quantity and quality, which makes the Paris region the first in France for the production of plaster. To the cavities dug by human hands are added those that were created naturally, especially in the north of Paris.
If the quarries of the capital are mapped, the possible consequences on the built surface are not sufficiently taken into account, in the eyes of Dominique Boussugue.
“My last letter on the subject to the Minister of Housing
(Editor's note: in July 2020)
remained unanswered.
As for the letter sent to the president, in 2018, I received feedback telling me that my mail will be transferred to different ministries [Ecological Transition and Housing].
" Then nothing.
The impact of global warming
Vera Matovic, architect and elected to the regional council of the Order of Architects of Ile-de-France, is not so alarmist.
“At the quarry service, everything is very well listed using detailed maps, which provides a large and exhaustive database on the nature of the land.
When we act as an architect, whether it is for a rehabilitation or a new construction, we first take into account the nature of the land.
It is not impossible to build on a quarry area, but on the other hand, it is not possible to build by weakening them.
We must, in these cases, fill them and it is very costly.
"
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Only, the real state of a career is evolutionary. “When we conduct surveys, it is a photograph at an instant T,” explains the architect. And it is impossible to photograph everything on the whole of a parcel, and therefore to list all the layers, of all the places of the ground. We are also on shifting lands. “In particular with the runoff of rainwater, floods and droughts which weaken the soil.
To better understand the evolution of the structure of quarries over time, particularly in the face of the succession of brutal climatic events, the National Institute for the Industrial Environment and Risks has set up an underground laboratory in Château-Landon, in the Seine. -and-Marne. Researchers are there, among other things, experimenting with “submersion with sudden flooding, to monitor in real time and understand the evolution of underground instability”, confides Xavier Daupley, head of the Geotechnical Risks Unit linked to the operation of the sub -ground. The first results tend to demonstrate, here too, a significant impact of global warming.
