Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale: observations, modelling and insights to improve monitoring systems
Abstract:Summary
Slope instabilities, including prone-to-fall rock columns, are known to exhibit clear vibrational modes. The resonance frequencies of these modes can be tracked by seismic instrumentation, allowing the rock column's mechanical and structural properties to be monitored, as well as providing precursors of imminent irreversible failures. In previous studies, superficial thermoelastic effects were assumed to drive daily fluctuations in resonance frequencies, but no qualitative or quantitativ… Show more
“…This observation suggests a thermally-dependent mechanism of the frequency drifts. A similar strong positive correlation between frequency and temperature has also been observed in other sites, where it was interpreted as an effect of stress stiffening of the external part of the rock mass (Colombero, Godio, & Jongmans, 2021;Geimer et al, 2022;Guillemot et al, 2022).…”
Fragile geological features must undergo frequent structural health assessments to prevent catastrophic failure events. The mechanical behavior of natural sites is largely guided by vibrations of the earth and environmental exposure, but damage is rarely assessed, except empirically. The Chauvet‐Pont d’Arc cave, a UNESCO World Heritage Site, represents a shining example of fragility that would benefit from monitoring. It is overhung by a rock column known as Abraham's pillar that extends out from the cliff like a natural tuning fork. For this study, we monitored dancing movements of this pillar for over 2 years to analyze its elastic response to weather conditions. Using ambient‐seismic‐noise‐based methods, we identified the pillar's first two natural resonance modes. Through extensive monitoring of the site, we observed the striking temporal evolution of these two resonance frequencies on hourly, daily, seasonal, and pluriannual scales in response to changes in air temperature and insolation. Based on thermo‐acousto‐elastic modeling with a simplified 3D geometric structure, we determined how thermally‐induced stress stiffening affects the rock material, by applying convective and radiative heat fluxes to the model. From the results obtained, we suggest a novel quantitative method based on daily observations that can estimate the level of damage within the rock material. Our work provides a foundation for distinguishing between reversible processes and damage for hazard studies in the frame of climate change. Such knowledge is crucial not only for the preservation of heritage sites but also for enhancing risk assessment protocols and informing conservation efforts worldwide.
“…This observation suggests a thermally-dependent mechanism of the frequency drifts. A similar strong positive correlation between frequency and temperature has also been observed in other sites, where it was interpreted as an effect of stress stiffening of the external part of the rock mass (Colombero, Godio, & Jongmans, 2021;Geimer et al, 2022;Guillemot et al, 2022).…”
Fragile geological features must undergo frequent structural health assessments to prevent catastrophic failure events. The mechanical behavior of natural sites is largely guided by vibrations of the earth and environmental exposure, but damage is rarely assessed, except empirically. The Chauvet‐Pont d’Arc cave, a UNESCO World Heritage Site, represents a shining example of fragility that would benefit from monitoring. It is overhung by a rock column known as Abraham's pillar that extends out from the cliff like a natural tuning fork. For this study, we monitored dancing movements of this pillar for over 2 years to analyze its elastic response to weather conditions. Using ambient‐seismic‐noise‐based methods, we identified the pillar's first two natural resonance modes. Through extensive monitoring of the site, we observed the striking temporal evolution of these two resonance frequencies on hourly, daily, seasonal, and pluriannual scales in response to changes in air temperature and insolation. Based on thermo‐acousto‐elastic modeling with a simplified 3D geometric structure, we determined how thermally‐induced stress stiffening affects the rock material, by applying convective and radiative heat fluxes to the model. From the results obtained, we suggest a novel quantitative method based on daily observations that can estimate the level of damage within the rock material. Our work provides a foundation for distinguishing between reversible processes and damage for hazard studies in the frame of climate change. Such knowledge is crucial not only for the preservation of heritage sites but also for enhancing risk assessment protocols and informing conservation efforts worldwide.
“…Similar mechanisms have been cited to explain reversible frequency drifts in slope stability monitoring (reviews by Colombero et al, 2021;Larose et al, 2015;Le Breton et al, 2021), often supported by results from careful finite element modeling to incorporate the unique geometric complexities of each site Guillemot et al, 2022). Observations of positive temperature-frequency correlations at daily scale are widespread and have been interpreted as stress-stiffening effects (e.g., Burjánek et al, 2018;Starr et al, 2015;Valentin et al, 2017).…”
mentioning
confidence: 68%
“…These features were: (a) the positive and steepening correlation of frequency to temperature over multiple months, (b) delayed frequency response to temperature on daily scales, and (c) a reversed and steepened correlation below 0° during freeze‐thaw cycles. In comparison to recent multiflux thermo‐acoustic‐elastic modeling of similar phenomena (Guillemot et al., 2022), we used simple harmonic temperature inputs and empirical stress‐ and temperature‐dependent elastic modulus to qualitatively replicate observed features, employing COMSOL Multiphysics to generate the coupled thermomechanical‐eigenfrequency solutions.…”
Section: Resultsmentioning
confidence: 99%
“…Infrared heat flux thus represents a potential modeling improvement, as Guillemot et al. (2022) combined it with acousto‐elastic theory to replicate daily resonance frequency variations of an unstable rock column. Last, we discuss the potential of an amplitude‐dependent explanation.…”
The resonance characteristics of freestanding structures contain information about bulk material and structural properties, providing a noninvasive and passive means to assess changing stability by monitoring modal parameters over time. However, efforts to identify precursory signs of damage or ultimate collapse using such parameters are often complicated by structural and material sensitivities to changing environmental conditions, such as temperature and moisture (e.g.
“…Demonstrated decreases in resonance frequencies before the failure of a rock column (Lévy et al., 2010) and a rock block collapse test (Taruselli et al., 2020), in addition to results of a study showing an increase in resonance frequencies of an unstable rock compartment after bolting reinforcement (Bottelin et al., 2017), highlight ambient vibration measurements as a valuable slope stability monitoring technique. Although numerous additional field‐based studies have attempted to capture frequency changes associated with landslide destabilization, often only environmentally driven recoverable changes are recorded (Bottelin, Lévy, et al., 2013; Burjánek et al., 2018; Colombero et al., 2018, 2021; Dietze et al., 2021; Guillemot et al., 2022; Häusler et al., 2021, 2022; Weber et al., 2018). In addition to resonance frequency values, seismic parameters including frequency‐dependent polarization azimuth and damping (e.g., Geimer et al., 2022) can be used to detect internal structural or material changes during stability monitoring (e.g., Häusler et al., 2022).…”
Ambient vibration measurements can detect resonance frequency changes related to rock slope instability damage or boundary condition changes during progressive failure. However, the impact of slope kinematics on resonance changes and the expected form and sensitivity of frequency evolution during destabilization require clarification to improve the implementation of this technique across diverse settings. Since instrumented rock slope failures are rare, numerical modeling is needed to study the anticipated spectral response from in situ monitoring. We used 2D distinct‐element modeling to evaluate the sensitivity and evolution of rock slope resonance behavior for slab toppling, flexural toppling, and planar sliding instabilities during progressive failure. Model simulations revealed that fundamental resonance frequency decreases between 20% and 60% with changes correlated with increasing length of open joints. Changes to higher‐order frequencies associated with landslide sub‐volumes were also detectable for cases with multiple fracture networks. Resonance behavior was most pronounced for failures dominated by steeply dipping open tension cracks, that is, flexural and slab toppling. Additionally, amplification patterns across the slope varied for the flexural toppling and sliding cases, providing potential new information with which to characterize landslide failure mechanisms using ambient vibration array measurements. Our results demonstrate landslide characteristics well‐suited for in situ ambient resonance monitoring and provide new data describing the anticipated changes in resonance frequencies during progressive rock slope failure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.