With the drought, many inhabitants of communes in the Alpes-Maritimes have noticed cracks in their house walls.
The mayors then filed requests for natural disaster classification of their municipality to allow their constituents to be covered by their insurance at the level of the work to be carried out.
These phenomena are due to the soils where the dwellings were built, which are clayey.
With the drought and then the intense rains, the earth retracted and swelled again, which created the damage actually observed, explains an architect specializing in the field.
“I have requests every day.
We are at 150 today but by Friday, it will easily rise to 170, ”exclaims Jean-Bernard Mion, mayor of La Colle-sur-Loup.
In a few weeks, residents of this town in the Alpes-Maritimes, which has almost 7,900, have found "cracks of several centimeters, sometimes in several places on their house", specifies the elected official at the head of this city for eight years, which ensures living “an exceptional situation”.
A situation due to drought according to them.
The mayor will then submit to the prefecture a request for natural disaster classification to allow his “citizens to carry out the work necessary for their safety”.
“This ranking is important for insurance coverage,” he continues.
Most of the people who see this damage are pensioners with a low pension and cannot incur these large costs.
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A classification in "catnat" not automatic
But a request to the prefecture does not mean an automatic classification as a natural disaster (catnat).
“The municipal requests will be examined in 2023 by the Ministry of the Interior, after sending the meteorological report from Météo-France on the phenomenon, generally during the first half of the year.
The analysis of the drought files is carried out by season or quarter, in order to take into account the slow kinetics of the phenomenon”, thus specify the State services.
In 2019, twelve had been registered in the department for this same cause and all had been rejected.
The same in 2020 and 2021, where six and eleven files had been submitted, one request is still under investigation.
According to the prefecture, twenty municipalities have made requests for this year.
A number that is also changing very quickly.
In one week, it was multiplied by two but it is still little compared to 2017, where 48 municipalities had requested recognition of canat for drought, 70.83% of them were recognized, further specifies the prefecture.
The clay soils in question
The situation in the Alpes-Maritimes is indeed particular.
Yves Justin, architect and member of the Architectes de l'urgence foundation, explains: “Everything comes from the nature of the soil.
The Bureau of Geological and Mining Research (BRGM) has found several areas of clay locally.
The drier this material is, the more it shrinks.
That is to say that if a building is built on this clay, it can go down to minus 60 cm.
But all it takes is the slightest rain for it to swell enormously.
And this is how the cracks are created.
In summary, the greater the difference between the rainy period and the dry period, the greater the risk of damage to buildings.
Added to this is “the scarcity of land”.
“We built in a clay zone due to a lack of space and with materials that play a role in the fragility of the buildings, explains the specialist.
Wood is more flexible than concrete or stone and therefore more resistant to movement.
It is noted that contemporary buildings deform more easily than old ones but that they are more easily repairable.
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Prevention rather than cure
And to repair, it is indeed expensive, confirms Yves Justin.
The techniques used consist of "injecting resin into the ground or installing metal piles, in concrete, which are placed under the buildings".
In order to guard against this work, the architect points out: “Before establishing a project, you have to do a sounding of the ground, even if there is an additional cost, it avoids other expenses afterwards.
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He adds: “You always have to take the terrain into account.
Why not use a slab, a stable platform, to maintain homogeneity but on a slope, it can aggravate the phenomenon.
» A common specificity in the hinterland of Nice.
“There are quite a few swelling clay zones but also alluvial ones, which have the same effects when faced with water,” he says.
And these phenomena could be accentuated.
“According to the Greek, the local IPCC, the predictions give higher rainfall in the years to come.
“According to the expert, it is then necessary to raise the awareness of the building trades but also the general public on “the culture of risk”.
“Setting up memory signs such as stelae with flood markers is very effective, especially locally where we have experienced severe flooding.
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