After informing the evacuees, the mayor of Saguenay Julie Dufour and an engineer from the MTQ met the press to explain the nature of the work which will consist of softening the slope where the landslide took place.
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Ms. Dufour first said she regretted all the outlandish theories circulating on social media about the causes of the landslide.
She then mentioned that as of today (Wednesday), a government employee will be working full time on the issue of financial compensation to citizens.
Denis Demers, from the Landslides section of the MTQ, explained that landslides in Quebec are quite common.
“There are 200 reports a year that we assess. In 60% of cases, landslides occur in the spring. The majority occur along waterways. It’s exceptional to have such a big slide in these conditions here,” he explained.
On April 11, a crack was reported to the City while there was snow on the grounds. After other interventions and initial evacuations, the MTQ recommended on April 26 a security perimeter and the installation of concrete blocks.
“It is certain that a slide was preparing, says Mr. Demers. But usually we have time to intervene before they happen. It can happen the next day, but it can also take months or years. The firm Englobe did not even have time to complete its soil study.
“There would have been deaths if we had not taken the temporary measures. The wall has done its job. It stopped the debris, the house tipped over due to the speed,” he added.
Heavy spring rains are responsible for the slide from the crack according to the expert. But as for the crack itself, he blames the nature of the ground, an unstable clay, combined with the large amount of snow received.
There would be no human factors here “factors responsible for 40 to 50% of the slides”, he takes care to add, inviting people not to do work at the top, in or at the foot of a slope. without authorization.
“But now, with bare and steep ground, it is certain that other landslides will occur,” he is convinced.
It was the possibility of “a very rapid clay flow that occurs without warning”, which led to the evacuation of 53 additional residences on June 18 and the construction of two dikes the following day.
He pictures this phenomenon where “the liquid on top makes the top crumble and creates a lot of energy” with the consistency of “an apple that you bite into compared to one that you pass through a mixer.
“The chances of a clay flow are very low. It happens once every two years in Quebec. But there was no chance to take, even if it came with a lot of inconvenience,” says Denis Demers.
Without the dikes, a clay flow could have come out of the perimeter.
look at the past
Surveys showing an ancient landslide to the northeast of the mountain “dating between 1,000 and 2,000 years ago” inspired engineers to determine the scale of the task at hand.
Four houses (five including the one that slipped) will certainly be demolished at the top of the embankment. If it is necessary to expand the softening area, two more at the top could be destroyed.
Two houses at the bottom of the slope – which will be in a safe zone once the work is completed – could be demolished if they were too damaged by the landslide.
Stating that the soil studies have not yet been completed, that it remains to know “the quantity of soil to be removed around the scar”, Mr. Demers indicated that “we know what to do, it is not complicated, but not yet how to do it.”
It excludes filling at the bottom of the slope. “It would be too dangerous for the workers.” This indicates that unfortunately the evacuees will not be able to return to their homes until the work is complete.
Since certain steps are not within his purview and the study has not been completed, Mr. Demers cannot give a precise timetable. But he estimates the work phase at around eight weeks “once the shovels are up”.
Once the slope has softened, all that remains is to remove the debris from the landslide, which measures up to 8m in height, and to put back vegetation.
What about the safety of occupants returning to their homes?
“In my work, you always say to yourself ‘would we sleep in this house’. And after the work, I would even be ready to buy one of these houses”, he guaranteed.