Multi-parameter monitoring of a solution mining cavern collapse: first insight of precursors

Abstract. In order to improve our understanding of the large-scale ground failure phenomena caused by old underground mining works, a solution mine was instrumented in 2004 prior to its collapse as part of its mining scheme. A permanent monitoring system was set up, including a high-resolution microseismic network linked to a surface field-displacement measurement system. The large amount of data transmitted for on-line processing provided daily insight into the evolution of the geological system. First, microseismic activity showed upward progressive failure migration throughout 2008 without any significant surface movement. Second, after two days of intensive brine extraction, a high microseismicity and energy release rate marked the failure of a thin and very rigid bed at a depth of 120 meters. This failure occurred 24 hours before the final collapse; it was followed by transient brine pressure signals, and by acceleration of the surface subsidence rate, reaching 1 m/h in the final phase. Résumé. Pour améliorer notre compréhension des phénomènes d’effondrement minier à grande échelle, nous avons instrumenté, en 2004, une cavité saline exploitée de manière intensive par dissolution jusqu’à l’effondrement des terrains de recouvrement. Un système de surveillance permanent comprenant un réseau microsismique haute résolution et un système de mesure de déplacement de la surface a ainsi été mis en place. Le traitement en quasi-temps réel des données a in er i