Slope instabilities, including prone-to-fall rock columns, are known to exhibit clear vibrational modes.
More associated failure modes can explain the triggering of rockfall. The combined use of traditional geological and geotechnical methods and more commonly used advanced remote sensing methods leads to better modelling, while the analysis of The aim of this manuscript is to make scientists and practitioners aware that investigation of rock mass cliffs and possible rockfall failures must not be based on usual methods without critical review of the obtained results and consequences. Although rockfall phenomena from the cliff face are relatively frequent, the kinematic analyses did not indicate a high probability of their occurrence. Kinematic analyses were performed on five cliff zones with slightly different structural features, indicating a relatively low probability of typical failures in the cliff rock mass that precede the rockfall occurrences. Both the traditional geological and geotechnical field survey and remote sensing surveys and analyses enabled the establishment of the structural model of the Raspadalica Cliff and the determination of the discontinuity sets and discontinuity features, such as orientation, spacing, persistence, roughness, discontinuity wall strength, aperture, degree of weathering of discontinuity wall, seepage conditions, and the presence and hardness of discontinuityįilling. This article presents the results of the geotechnical study of the cliff based on a traditional geological and geotechnical field survey and remote sensing analysis. The Raspadalica Cliff is an almost vertical 100 m high limestone cliff with a railway lineĪt its foot and is known for numerous rockfall occurrences in the past. In this study, a combination of traditional geological and geotechnical field surveys and remote sensing techniques were employed to detect and mapping of the discontinuities and discontinuity sets, orientation and dip of discontinuities, and other discontinuity features necessary for the analyses of rockfall occurrences and their consequences.
Due to the increasing use of UAV photogrammetry and the SfM technique to create 3D HRPC models, various automatic and semi-automatic techniques and methods have been developed to detect and map the discontinuities and discontinuity sets 28,31, orientation and dip direction of discontinuities 48,49, spacing of discontinuities 32,37,42,46,49,53,63,65,70,72,, persistence of discontinuities, and roughness of discontinuities. After the establishment of the 3D HRPC model described previously, the model was analyzed to identify the main characteristics of the rock mass structure, such as the detection and mapping of the discontinuities and discontinuity sets, orientation and dip of discontinuities, spacing of discontinuities, persistence of discontinuities, and roughness of discontinues, as well as determination of rock block volumes. 1c corresponding to the cliff area framed in reddish-orange in Panel a. (g) Extract from the 3-D geological model of Fig. 1b corresponding to the cliff area framed in reddish-orange in Panel a. (f) Extract from the 3-D photorealistic model of Fig. (e) Same as Panel d but with an emissivity ε of 0.95. The average temperature of each black frame (50 × 50 pixels) is indicated under the frames.
(d) Detail view of the cliff area framed in reddish-orange in Panel a. (b) Detail view of Boot Flake framed in yellow in Panel a. The white circles and white arrows highlight cold thermal anomalies that correspond respectively to lighter-colored rock areas and overhanging areas. The black frame shows the position of the reflective paper as well as the resulting reflective apparent temperature (18.6 ☌ coldest pixel) measured after calibration. (a) IRT panorama (2820 × 1525 pixels -30 stitched thermal images) of the southeast face of El Capitan on 8 October 2015 at 17:45 PST. Key to abbreviations: Kap = aplite dikes Kec = El Capitan Granite Kd = diorite of North America Kdo = dikes of the Oceans Klt = Leaning Tower Granite Kt = Taft Granite ε = Emissivity. Classification of thermal signatures of El Capitan geologic units.
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