A hole about ten meters deep.
At the end of February, the ground suddenly gave way on rue de Vesoul, one of the main access routes to Besançon (Doubs), part of which still remains impassable.
Studies carried out in recent days have discovered the existence of an incredible underground system.
To better understand this network, the city and the department in charge of the work called on a hydrogeologist: Pascal Reilé, a fine connoisseur of karst soils.
The road not about to reopen
“On Monday we injected a dye into the hole called fluorescein.
It is a green liquid that is harmless to the environment and aquatic fauna.
We added 10 m3 of water to facilitate the circulation of water in this fault, indicates the scientist in charge of operations.
After two days, our sensors spotted this dye in a source in the city center, 3 km away.
Clearly, the hole communicates with vast galleries located under the city.
How can we explain the sudden appearance of this geological phenomenon?
“We see that it is a functional system.
Rainwater underground was able to release the sediments which contributed to this filling.
Droughts and human activities also favor this underground disorder,” continues Pascal Reilé.
It will take several weeks, if not months, before this road reopens to traffic.