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The dynamic response of prone-to-fall columns to ambient vibrations: comparison between measurements and numerical modelling

Abstract : Seismic noise measurements (ambient vibrations) have been increasingly used in rock slope stability assessment for both investigation and monitoring purposes. Recent studies made on gravitational hazard revealed significant spectral amplification at given frequencies and polarization of the wave-field in the direction of maximum rock slope displacement. Different properties (resonance frequencies, polarization and spectral ratio amplitudes) can be derived from the spectral analysis of the seismic noise to characterize unstable rock masses. The objective here is to identify the dynamic parameters that could be used to gain information on prone-to-fall rock columns' geometry. To do so, the dynamic response of prone-to-fall columns to seismic noise has been studied on two different sites exhibiting cliff-like geometry. Dynamic parameters (main resonance frequency and spectral ratio amplitudes) that could characterize the column decoupling were extracted from seismic noise and their variations were studied taking into account the external environmental parameter fluctuations. Based on this analysis, a two-dimensional numerical model has been set up to assess the influence of the rear vertical fractures identified on both sites on the rock column motion response. Although a simple relation was found between spectral ratio amplitudes and the rock column slenderness, it turned out that the resonance frequency is more stable than the spectral ratio amplitudes to characterize this column decoupling, provided that the elastic properties of the column can be estimated. The study also revealed the effect of additional remote fractures on the dynamic parameters, which in turn could be used for detecting the presence of such discontinuities.
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Submitted on : Friday, August 21, 2020 - 8:06:21 AM
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J. Valentin, A. Capron, D. Jongmans, L. Baillet, P. Bottelin, et al.. The dynamic response of prone-to-fall columns to ambient vibrations: comparison between measurements and numerical modelling. Geophysical Journal International, Oxford University Press (OUP), 2016, 208 (2), pp.1058-1076. ⟨10.1093/gji/ggw440⟩. ⟨hal-02019269⟩

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