EGU21-6390
https://doi.org/10.5194/egusphere-egu21-6390
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Monitoring Rock Slope Instabilities Using Frequency Domain Decomposition Modal Analysis

Mauro Häusler1, Clotaire Michel2, Jan Burjánek3, and Donat Fäh1
Mauro Häusler et al.
  • 1ETH Zurich, Institute of Geophysics, Department of Earth Sciences, Zurich, Switzerland
  • 2Risk&Safety AG, Aarau, Switzerland
  • 3Institute of Geophysics of the Czech Academy of Sciences, Prague, Czech Republic

Measuring ambient seismic vibration provides a promising tool to monitor unstable rock slopes due to its independence from actual surface deformations. It is generally observed that the seismic wavefield, arising from ambient vibrations, polarizes perpendicular to open fractures and that unstable slopes exhibit strong wavefield amplifications compared to stable reference sites. Rock slope instabilities dominated by deep persistent fracture sets exhibit normal mode behaviour due to standing wave phenomena within individual compartments of the unstable volume. Techniques to assess such behavior are well established in mechanical and civil engineering to assess the dynamic response and possibly the structural integrity of the structure studied.

 

We performed enhanced frequency domain decomposition modal analysis on ambient vibration data acquired in real-time on an unstable rock site with a volume larger than 150,000 m3 near Preonzo, Switzerland. We tracked the resonance frequency and normal mode polarization of the first two modes over a period of four years. In addition, we show the development of the modal damping ratio of the fundental mode over time, which is a measure of energy dissipation within and out of the system. We found that the dynamic properties of the rock structure experienced annual variations and that they are primarily controlled by temperature and only secondarily by the exension and closure of large-scale fractures. Even though no large slope failure was observed during the monitoring period, the dataset provides a reference model for ongoing slope monitoring, as the resonance frequency and damping ratio is expected to change significantly prior to failure.

How to cite: Häusler, M., Michel, C., Burjánek, J., and Fäh, D.: Monitoring Rock Slope Instabilities Using Frequency Domain Decomposition Modal Analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6390, https://doi.org/10.5194/egusphere-egu21-6390, 2021.