Structural Characterization of a Toppling Rock Slab From Array‐Based Ambient Vibration Measurements and Numerical Modal Analysis

Abstract

Assessing and mitigating hazards associated with rock slope failures requires detailed knowledge of instability geometry, material properties and boundary conditions (

Coevolution of Rock Slope Instability Damage and Resonance Frequencies From Distinct‐Element Modeling

“…For the flexural toppling and sliding models, failure was controlled by the strength properties of the main joint set, and we kept the strength properties of the Voronoi joints constant to simulate the failure of intact rock. In the case of the Courthouse Mesa instability the rear discontinuity did not initiate along a predefined joint surface (e.g., Bessette‐Kirton et al., 2022). Therefore, for the slab toppling model, we applied the same properties to the main discontinuity and Voronoi joints, since the rupture of the main discontinuity involves fracture of intact rock rather than predefined joint surfaces.…”

“…These were selected to maintain an approximately similar failure area across all kinematic modes. Since the Courthouse Mesa field site, which is associated with the slab toppling case, consists of massive sandstone (Bessette‐Kirton et al., 2022), we chose to use the properties of sandstone for all scenarios to maintain consistency across models. We kept the following material properties constant: density = 2,000 kg/m 3 (Moore, Geimer, Finnegan, & Thorne, 2018), Young's modulus = 10 GPa (based on data from Entrada, Navajo, and Wingate Sandstones in Utah; Alikarami et al., 2013; Moore, Geimer, Finnegan, & Thorne, 2018; Skurtveit et al., 2021), and Poisson's ratio = 0.2.…”

“…Slab toppling failures are common in granitic rocks (e.g., Colombero et al., 2018), anaclinal slopes in hard limestone cliffs (Frayssines & Hantz, 2009) and interbedded sandstones and mudstones, where undercutting from differential weathering initiates toppling and the propagation of tension cracks at the crest of the slope (Wang et al., 2013). This case was chosen because it is common to many investigations of resonance in unstable rock compartments (Bottelin et al., 2017; Bottelin, Jongmans, et al., 2013; Bottelin, Lévy, et al., 2013; Colombero et al., 2018, 2021; Lévy et al., 2010) and reflects the geometry of our Courthouse Mesa field site, which was used for comparison with model results (Bessette‐Kirton et al., 2022). We also examined two common kinematic failure modes: flexural toppling and planar sliding (Figures 1b and 1c).…”

“…Analysis of spectral properties in relation to displacements and joint fracture enabled assessment of landslide frequency evolution to identify failure scenarios that are well‐suited for in situ ambient resonance monitoring and provide new information on the form and sensitivity of anticipated frequency responses. We compare model outputs with field analogs, including the Courthouse Mesa rock slope instability in Utah, USA, for which we have conducted field characterization and long‐term monitoring (Bessette‐Kirton et al., 2022).…”

Modal Analysis of a Lava Tube Roof Complex: Tabernacle Hill, Utah, USA

“…While most geophysical or remote sensing techniques are generally employed for mapping cavity networks, structural characterization of potential ground instabilities is mainly conducted using geomechanical testing and invasive field surveying techniques (Margherita et al 2018;Bastidas et al 2022). Nevertheless, recent studies have highlighted that ambient vibration modal analysis can be used to reveal mechanical and dynamic material properties of ground and slope instabilities, as well as their extent and structure, by identifying natural resonance frequencies, local site amplifications and polarization attributes (Kleinbrod et al 2019;Bessette-Kirton et al 2022;Geimer et al 2022). In particular, the combination of experimental modal analysis and numerical eigenfrequency modeling has been used to improve geologic models by constraining material properties (Moore et al 2018;Geimer et al 2020;Müller and Burjánek 2023) and has provided valuable new insights on local boundary conditions and structural characteristics (Colombero et al 2017;Bessette-Kirton et al 2022).…”