Laboratoire de Mathématiques Raphaël Salem

UMR 6085 CNRS - Université de Rouen Normandie

Underground cavities known as "marnières", typically consisting of a cavity 1 to 3 meters high and connected to the surface by a vertical shaft 20 to 40 meters deep and 1 to 2 meters in diameter, were historically dug by farmers—especially during the 19th century—to extract chalk used as fertilizer.

However, these structures were often not officially declared, due to the high costs associated with such declarations. As a result, their exact locations remain largely unknown. The issue today is that many of these shafts were either never properly sealed or only partially filled with heterogeneous materials. With the effects of climate change, the risk of collapse under buildings, roads, and other infrastructure has increased.

The objective of my thesis is to evaluate whether a novel detection method—using an infrared camera mounted on a drone—can identify these underground cavities. To support this, numerical simulations using FreeFem++ are carried out to analyze the thermal anomalies generated by such structures, based on real point cloud data from marnières in the Normandy region.