At the bottom of the hole. It is no longer even in the shadows that he works, but downright in total darkness. However, without this man and the members of his team, many tragedies could not have been avoided. He is Gaëtan Cheppe, an official of the town hall of Lille whose role is to monitor what is happening under the feet of the inhabitants. At the head of the joint service for underground quarries, this 50-year-old tells us about his job as an explorer of old limestone mines which make a part of the metropolis a real Swiss cheese.
Over the year, the six employees of Gaëtan Cheppe’s department, including himself, spend an average of one month underground. “It represents around 700 hours to crisscross the galleries of the old limestone mines which extend under a dozen municipalities of the metropolis”, explains the head of this service. On the surface, this is equivalent to 170 football fields, “and still, we only know 80% of these quarries, the rest is yet to be discovered”, he assures.
“There is no school to learn how to diagnose the state of a career”
A chemist by training, and town hall employee in charge of risk management, Gaëtan Cheppe did not have much of a speleologist at the start. But when the department handed over to the municipalities the management of the surveillance of their basement, it did not hesitate: “We started with two, trained by the specialist of the department because there is no school to learn how to diagnose the state of a career. “Today, he is unbeatable, especially on stilettos, a method of extracting chalk that can not be found anywhere else than in the Lille metropolis.
Whether in “pillar chambers” or “catiches”, the exploitation of chalk stopped at the beginning of the 20th century. Since then, the old mines, which can reach 15 m deep, have been covered by urbanization. “Our main activity is to descend into these shafts and check their condition, in particular to avoid any risk of collapse. This can lead to preventive reinforcement work or sectorized filling,” explains Gaëtan Cheppe. Thus harnessed like speleologists, the men of the service of the careers inspect at least once a year each known mine. “What happens most often is that the plug placed at the time to prevent access to the well falls. You then find yourself with a hole 2 m in diameter, 10 m deep, ”insists the specialist.
“There are more and more intrusions”
Wearing, accidents are rare. The department’s on-call service manages an average of only ten urgent interventions per year. But when it does, it’s spectacular. Last May, in a commercial area of Seclin, the ground gave way behind a shop, leaving a gaping hole 5m deep by 10m in diameter. “The last intervention that marked the service the most was January 1, 2022. We had been contacted to find partygoers who had decided to spend New Year’s Eve in a catiche and who had gotten lost”, recalls the chef on duty. If a tragedy could have been avoided, Gaëtan Cheppe nevertheless fears these unconscious explorers: “There are more and more intrusions, often on the part of people who do not respect the places and who are unaware of the dangers”, deplores- he. Indeed, in addition to the risk of collapse or that of getting lost, some quarries display very low oxygen levels in which prolonged exploration can lead to asphyxiation.
Regularly, the quarry service explores the territory in search of new cavities. “Three years ago, we came across a 10,000 m2 quarry in Lille-Sud. It’s so thrilling to enter a place that hasn’t seen a human being for three centuries,” he enthuses. Especially since some mines conceal treasures. Sculptures made by miners, frescoes, objects abandoned as they are. “To date, the oldest inscription that we have discovered dates from 1626,” says Gaëtan Cheppe. Without forgetting the underground lakes and their limpid water, the cathedrals formed by the highest catiches… “It’s a profession of passion”, he acknowledges. Indeed, there are worse as an office.