Experimental study towards the investigation of scale effects in 3D granular slides

Granular slides can be defined as gravity-driven rapid movements of granular particle assemblies mixed with air and often also water. This ubiquitous phenomenon is not only observed in industrial applications such as hoppers, blenders and rotating drums, but also in natural contexts in the form of landslides, rockslides and avalanches. These granular slides in nature may cause devastation and human losses in their run-out path and indirect effects such as landslide-tsunamis, landslide dams and glacial lake outburst floods. The investigation of granular slides in nature is challenging due to the dangers in accessing the landslide locations in a timely manner and the challenges in predicting when and where they occur. Here, we use well defined and controlled three-dimensional (3D) laboratory experiments, building up on own (Kesseler et al., 2020*) and other studies, which were commonly limited to two dimensions (2D). The primary aim of the current study is to extend the scale effects investigation of Kesseler et al. (2020) to 3D and to provide new physical insight into 3D granular slides.

 

The experimental setup from Kesseler et al. (2020) has been upgraded from 2D to 3D by extending the side of the ramp and runout zone. The upgraded versatile 3 m long and 1.5 m wide ramp transitions via a curved section into a 3 m long and 2 m wide runout area. The measurement system, consisting of cameras recording the slide evolution and for general observations and a photogrammetry system to investigate the slide deposit shape including the runout, has been complemented with two laser distance sensors measuring the slide thickness along its centreline at two distinct positions during slide propagation.

 

In this initial study, we explore two different slide volume limits and, surprisingly, found a negative correlation between the slide volume and runout distance. Moreover, we identified a positive correlation between the slide thickness and slide volume. A positive correlation has also been identified between the maximum deposit height and the initial slide volume. Further, the good test repeatability is demonstrated with a detailed quantification and presentation of the characteristic variation plot at different time instances, involving the slide centroid and front velocities, the maximum slide thickness, the slide side expansion ratio and the locations of the slide deposit front- and backlines.

 

These findings may ultimately contribute to landslide and avalanche hazard assessments by providing an efficient and improved prediction of the slide kinematics, the slide evolution and the slide deposition features such as the runout distance. Moreover, once all experiments are conducted at different scales, we hope to be able to quantify and understand scale effects of granular slides and to improve the upscaling procedure from laboratory scale to nature.

 

 

*Kesseler, M., Heller, V., Turnbull, B. (2020) Grain Reynolds number scale effects in dry granular slides. Journal of Geophysical Research-Earth Surface 125(1):1-19.