Monitoring Rock Slope Instabilities Using Frequency Domain Decomposition Modal Analysis

Session: Environmental and Near Surface Seismology: From Glaciers and Rivers to Engineered Structures and Beyond
Type: Oral
Date: 4/29/2020
Time: 08:45 AM
Room: 110 + 140
Description: 

In the past decade, ambient seismic vibration measurements have been increasingly used to characterize unstable rock slopes. Such measurements are complementary to geodetic and remote sensing techniques, which are primarily based on surface displacement data. It is generally observed that the seismic ambient 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 studied structure.

We performed enhanced frequency domain decomposition (EFDD) modal analysis on ambient vibration data acquired on an unstable rock site with a volume larger than 150'000 m3 near Preonzo, Switzerland. We show that the clear polarization pattern identified by EFDD and the high ground motion amplification compare well to previous studies that are based on site-to-reference spectral ratios and time-frequency polarization analysis. EFDD additionally provides the damping parameters (energy dissipation) and facilitates the detection of higher modes. Both, damping and higher modes, support the geometrical interpretation of the instability. The resulting EFDD parameters are expected to change with increasing damage within the rock slope, either rapidly after strong ground shaking or due to other external loading or gradually by progressive degradation of the rock mass over time. We show EFDD results of a four year near real-time monitoring period at Preonzo, correlate the dynamic parameters of the rock mass with meteorological data and compare them to extensometer measurements.

Presenting Author: Mauro Häusler

Authors