Seismic noise spectral analysis techniques to monitor unstable rock blocks

This study presents the analysis of the ambient seismic noise collected on a small limestone block that was forced to fail during a field test. We compare different spectral analysis techniques with the objective of investigating their performances and suitability to monitor the rock block stability over time. Ambient vibration datasets were first pre-processed before the spectral analysis was carried out. The outcomes clearly show a variation in spectral content when approaching rock ultimate failure, especially when considering spectrograms and horizontal-to-vertical spectral ratio curves. This agrees with the assumption that the collapse of an unstable rock is preceded by a drop of its natural frequency due to the deterioration of rock bridges. The obtained results confirm the potential of ambient noise spectral analysis as a reliable tool to improve our capabilities of rock failure forecasting.