Mining Induced Seismicity - Monitoring of a Large Scale Salt Cavern Collapse

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To improve our understanding in large scale ground failure phenomenon induced by old underground mining works, a field experiment was undertaken in collaboration with the SOLVAY mining company: a solution mine was instrumented in 2004 previously to its collapse which was triggered in February 2009, as part of the mining scheme. This solution mine is located in the Lorraine salt basin (France). To monitor the cavern collapse, a multi-parameter system featuring high resolution microseismic linked to ground surface leveling (tacheometer and GPS-RTK) was used. The data transmitted for on-line processing offered daily insight of the evolution of the underground cavity. The early signs of unstable evolution were detected during spring 2008: shifts in microseismic background regime end recurrent microseismic episodes were associated to a general upwards process of rock failure of the roof cavern, with no ground surface movement detected. The high microseismic regime of the cavern has convinced the operator to trigger the collapse by brine pumping. Three main microseismic regimes were then observed, each being well correlated with changes in both the surface subsidence rate and the brine level in the cavern.