Interpretation of convergence movement in room and pillar mining by integrating creep of salt and swelling of marl under water effect

Abstract : The St Laurent Einville salt mine was mined by abandoned room and pillar with an average recovery rate of 75%. Unlike the roof where a small salt crown pillar was abandoned, the pillars are directly based on the highly stratified marl. Seepages of salt water were observed at different locations in the mine in particular at the emergency shaft. The convergence measurements highlighted a discrepancy between the different stations. The analysis made showed clearly that the acceleration observed at the station located near the emergency shaft is due mainly to a movement coming from the footwall which is directly linked to water inflow. The mechanism proposed to explain this behavior is based on pillar punching in the footwall and failure of the stratified marl by excess of bending, water intrusion acted as initiator and amplifier of the phenomenon. To validate this mechanism, a numerical model including salt creep and marl swelling under water effect was developed and compared to in-situ measurements.