Understanding the instability mechanisms of chalk mines in presence of water (France)

International audienceIn January 1910, the 100-year flood of the Loing River caused the tragic collapse of an underground chalk mine at Château-Landon (France), which resulted in the death of 7 people. In this valley, three other underground chalk mines had already collapsed. The hydrogeological analysis of the site and the geomechanical studies carried out on the chalk enabled to elaborate a 3-stage collapse scenario: (1) exceptional rainfall generating intense flooding of the Loing, which plays the role of a hydraulic dam and causes (2) a rise of the chalk aquifer, which invades (3) the lower parts of the mine and weakens the pillars until they collapse. To evaluate this scenario, the Royer mine, the last underground mine still intact in this sector, was thoroughly studied. This study included a complete 3D scan of the mine, modelling of its geomechanical behavior and geomechanical and hydrogeological monitoring that will last several years