Rock stability as detected by seismic noise recordings - Three case studies

In this work, we present the analysis of seismic noise recordings we performed in northern Italy. Surveys were carried out on large rock blocks and pillars at two sites, namely Pietra di Bismantova and Torrioni di Rialba, and on a small limestone block that was forced to fail during a controlled collapse test. Our aim is to identify the resonance frequencies of the investigated rock structures, to correlate them with the geological features of each site and to track their possible variations across following measurement epochs. Within this perspective, ambient vibrations recordings have been processed with a standard sequence and noise spectra and spectral ratios techniques have been evaluated. The obtained results showed resonance frequency variations appear to be correlated with both meteorological parameters, such as wind and temperature fluctuation, and the breakage of rock bridges. This study confirms the potential of ambient vibrations to provide information about the inner structural setting of rock masses, which is a key parameter for monitoring purposes and mitigation strategies.