Characterization of a Toppling Rock Slab Instability with Ambient Vibration Array Measurements

Abstract:

In-situ ambient vibration measurements can be used to determine material and dynamic properties of rock structures and are becoming increasingly utilized in slope stability assessments. To aid in the characterization of a toppling sandstone slab, located near Moab, Utah, and delineated by a ~500 m-long rear fracture, we deployed a temporary nodal geophone array along the unstable cliff. Comparison of spectral peaks and cross correlation analyses across the array allowed us to identify and visualize several resonant modes between ~1-10 Hz. Additionally, we used the results of our seismic array measurements to help calibrate a 3D finite element model of the unstable rock slab in order to better constrain the crack depth and lateral boundary conditions. Interpretation of seismic data in conjunction with modeling results indicates that the crack delineates an interconnected slab with clearly expressed transverse and longitudinal bending modes. The results of this study aim to provide a better understanding of the failure mechanism associated with the instability and demonstrate the value of ambient vibration array measurements in the characterization of unstable rock slopes.