Author(s): Jan Hrebrina; Slaven Conevski; Leif Lia; Elena Pummer
Linked Author(s): Slaven Conevski, Leif Lia, Elena Pummer
Keywords: Boulder transport; Incipient motion; Critical conditions; Shield number; Physical experiment
Abstract: In high mountain regions, isolated boulders can present significant threats by clogging or damaging the inlets of hydraulic structures, causing internal abrasion of tunnels or pipes, disrupting operations, blocking intakes, and impacting habitats. At the same time, they can serve as indicators of historical flood events, helping to determine the flow magnitude that mobilized them. Predicting their motion is essential for infrastructure design, natural hazard management, and understanding geomorphological processes. The movement of boulders can be triggered by landslide-induced impulse waves, flood events, as well as by external forces such as impacts from other boulders, landslides, or debris flows. However, studies investigating the conditions for the initial movement of solely isolated boulders are scarce. Hence, in this study, the initial motion of an 80 mm concrete cube was used as a scaled boulder abstraction to facilitate the fundamental analysis of boulder motion. A smooth, horizontal metal bed was used under uniform flow conditions, with the discharge gradually increased until the boulder began to move. A total of 20 tests with the same boulder position and orientation showed a wide range of Shields parameter values required to initiate boulder movement. Interestingly, the boulder started to move under two conditions: partially submerged and fully submerged. Future research will include tests with different bed gradients and roughness conditions, the influence of waves, as well as varying cube and boulder shapes and sizes, and will compare the results with those of this study. Additionally, the hydrodynamic forces influencing boulder incipient motion will be analyzed both numerically and experimentally.
Year: 2024