Thermomechanical Response of Freestanding Geologic Structures to Environmental Stressors: Sensitivity Characterization Using Resonant Mode Monitoring

Abstract:

The monitoring of freestanding geologic structures using ambient resonance is increasingly common as a passive and noninvasive tool to assess stability and identify permanent damage. However, interpretation of changing resonant characteristics is often complicated by structural and material sensitivities to varying environmental stressors, such as moisture and temperature. The slender spans of rock arches, which give the structures their notable fragility, create clear and predictable resonant modes, making arches ideal candidates for constraining environmental sensitivity. We used 15 months of continuous monitoring at one arch to develop empirical relationships between temperature, moisture, and resonance, supported by thermomechanical finite-element modeling employing a stress-dependent material stiffness. We tested this model against other arches sharing similar lithologies, but with varying shapes and sizes, finding correlation with temperature sensitivity, lag times, and arch dimensions. Our results suggest that temperature sensitivity of resonance is present in nearly all arches, with variations largely controlled by simple thermal diffusion effects. By characterizing the recoverable response to the ambient environment, we gain insight into how arches and other freestanding structures respond to stress and improve our ability to monitor for permanent structural changes.