Friction angles at sandy beaches from remote imagery

Abstract

The rigour of extracting friction angles, and eventually lower-bound bearing strength, in sandy beach settings through slope angles determined from digital images (visual spectrum) is explored. Digital images of topographic sand features using hand-held cameras, an unmanned aerial vehicle and a panchromatic satellite sensor are analysed to determine average slope angles using three-dimensional reconstruction. Greyscale gradients and shadows are utilised in the satellite images to extract slope estimates. The slope angles matched tilt table results of samples from the same locations at the Duck, NC, and Claytor Lake, VA, field sites. Direct shear testing of sample material suggest friction angles of ∼33° and ∼35°, respectively. The authors test a potential pathway to derive lower-bound bearing strength using these remotely sensed slope angles. Preliminary results are encouraging, but likely sensitive to the impact of moisture content, differences between the maximum and the observed slope angle and internal friction angles.

Modeling the Morphodynamics of Coastal Responses to Extreme Events: What Shape Are We In?

“…Although simple parameterizations have provided adequate results in terms of slumping rate and postevent profile shape, more physically based modeling of dune and foreshore processes based on soil-mechanics principles may be the key to improving models of dune stability and beach trafficability. Recent progress in sensors to rapidly characterize key soil properties, such as sediment strength and its relationship to wave energy, friction angle, and moisture content (Stark et al 2017, Albatal et al 2019, may lead to improved modeling of soil mechanics in morphodynamic models. However, with improved physical description of these processes will come a demand for more data regarding soil moisture, geological framework, and sediment characteristics, for which observations at the appropriate scale are often lacking.…”

Geotechnical Measurements for the Investigation and Assessment of Arctic Coastal Erosion—A Review and Outlook

“…This can be further strengthened by fusion with traditional data collection methods, which could also be more strategically deployed based on initial remotely sensed data (see Section 4.1). As another example, deriving the density and friction angles of coarse-grained sediments, as shown by [87,89], could also improve the assessment of erodibility of sandy shorelines and may assist with the identification of possible erosion hotspots which require further investigation. However, satellite-or UAV-based remote sensing has so far been rarely used to derive geotechnically relevant information in Arctic environments, and this may also be further complicated by soil transition between frozen and thawed and permafrost [90,91].…”

Effects of Shell Hash on Friction Angles of Surficial Seafloor Sediments near Oysters

“…Note that friction angle is defined here as the peak effective stress friction angle (which is synonymously used with secant friction angle). When there is no confining pressure and no external load (other than the sediment's self-weight), the secant friction angle is equal to the angle of repose, which is the maximum angle that a pile of coarse-grained sediment is stable at its loosest state (Holtz et al 2011;Briaud 2013;Stark et al 2017;Al-Hashemi and Al-Amoudi 2018). Therefore, a higher secant friction angle observed for a shell hash-sand mixture relative to sand only is generally expected to result in the sediment having a higher resistance to erosion.…”