Instability mechanisms of chalk mines in presence of water : feedback from the collapse of the Baulieu mine (France)

Vincent Renaud (1) , Auxane Cherkaoui (1) , Jean-Marc Watelet (1) , Philippe Gombert (1)

1 INERIS - Institut National de l'Environnement Industriel et des Risques

The weakening of chalk mechanical characteristics under the influence of ageing and flooding/unflooding cycles may be at the origin of dramatic collapses. For illustration, in January 1910, the collapse of the underground chalk mine known as "Beaulieu" (Chateau-Landon, France) caused a large landslide, leading to the death of seven people and destroying several houses. The sudden nature of the event and its concomitance with the flooding of the mine by the nearby “Loing” river have raised the hypothesis that the collapse was caused by the degradation of the mechanical properties of the chalk induced by the increase of saturation degree. To investigate this hypothesis and more generally, to better understand the mechanisms at the origin of instabilities in chalk mines, a large program including a laboratory characterization, in situ instrumentation and numerical modelling, was set up in 2011. Three underground chalk mines of the Paris Basin (France), including Chateau-Landon, were selected to study the geomechanical behavior of chalks subjected to changes in water saturation degree. Various series of laboratory tests have been undertaken, which allowed to advance in the understanding of the physical and mechanical water-chalk interactions. However, the extent of the phenomenon observed in Chateau-Landon could not be explained only by the reduction of the mechanical properties of chalk in the presence of water. In this context, it was decided to study the behavior of a neighboring and still accessible mine known as "Royer", located less than 500 m from the Beaulieu mine. This mine appeared as the ideal site to get further insights into the mechanisms responsible for this collapse. Indeed, this mine has extracted a similar material, and showed signs of instability in 2016 following exceptional climatic events for this region (177 mm of precipitation for the month of May and important flood of the Loing).

Domaines: Sciences de la Terre

Vincent Renaud, Auxane Cherkaoui, Jean-Marc Watelet, Philippe Gombert. Instability mechanisms of chalk mines in presence of water : feedback from the collapse of the Baulieu mine (France). 1st International symposium on computational and geoenvironmental geomechanics for underground and subsurface structure (COGGUS2), Feb 2019, Nancy, France. ⟨ineris-03319915⟩