Detection of underground instabilities in an old limestone quarry through acoustic monitoring

The presence of abandoned and unstable underground cavities can give rise to a potential risk of surface collapse, particularly alarming when the presence of buildings is attested on the surface. The INERIS (Institut National de l'Environnement Industriel et des Risques, France) has carried out many studies, in recent years, investigating the effectiveness of several methodologies to monitor the evolution of the damaging mechanisms. During 2012 the Brasserie quarry, an old limestone mine (Paris, France) was instrumented with microphones to detect the acoustic waves generated by the collapse of blocks from the roof and the walls of the cavity. A series of tests were carried out to determine the propagation characteristics. Preliminary data processing concerned the event classification and the analysis of the signal-to-noise ratio (SNR). In the present paper, after the description of the case study, the preliminary results and the description of the upcoming works and expectation will be outlined.