Project Partner

Civil Engineering Office, Canton of Grisons

ETH Zürich

Geological Office

BTG Büro für Technische Geologie AG

Services Provided

• Measurement of ambient vibrations for 90 minutes with 23 highly sensitive seismometers.
• Analysis of seismic amplification to assess the degree of rock fragmentation and map the extent of instability.
• Identification of different structural dynamic compartments within the instability using modal analysis.

Project Description

Since 2005, deformations have been measured on a retaining wall along a turning bend on the Duvin road in the canton of Graubünden. This problem persisted even after the construction of two back-anchored concrete pillars in 2018. As part of a pilot project, the possibilities of passive seismic mapping were demonstrated in order to quickly assess the extent of the instability.

Using 90-minute recordings of ambient vibrations with 23 portable seismometers, the analysis of seismic amplification showed that the rock in the area directly adjacent to the renovated section has a high degree of fragmentation with amplification factors > 7. Using modal analysis, different compartments of the instability were also identified. This demonstrates the potential of passive seismic methods for rapid geophysical mapping of slope instabilities and provides valuable baseline information for monitoring and planning future measures.