Flow-like landslides, such as debris flow and rock avalanche, occur in mountainous regions and pose significant risks to human lives and infrastructures. The interactions among particles in flows are subjected to intensive shear and collisions. The size and concentration of the particles involved in a flow govern the rheological behavior and the prevailing impact mechanisms against structural countermeasures. The high stress and energy levels experienced by the particles in large-scale landslide events often result in particle breakage, which is generally not considered when modelling flow-like landslides. The extent to which particle breakage affects macroscopic and mesoscopic stresses as a flow impacts a barrier poses a challenge to scientists and engineers.

In this study, th...[ Read more ]

Flow-like landslides, such as debris flow and rock avalanche, occur in mountainous regions and pose significant risks to human lives and infrastructures. The interactions among particles in flows are subjected to intensive shear and collisions. The size and concentration of the particles involved in a flow govern the rheological behavior and the prevailing impact mechanisms against structural countermeasures. The high stress and energy levels experienced by the particles in large-scale landslide events often result in particle breakage, which is generally not considered when modelling flow-like landslides. The extent to which particle breakage affects macroscopic and mesoscopic stresses as a flow impacts a barrier poses a challenge to scientists and engineers.

In this study, the impact behavior of mono-disperse and bi-disperse flows against a rigid barrier was modelled using the geotechnical centrifuge. The centrifuge enables stress and energy levels to induce particle breakage. More importantly, centrifuge scaling laws can be leveraged to model larger flow volume and particle size. Two different g-levels were investigated, specifically 22.4 g and 44.8 g. By modelling flows at two different g-levels, modelling of models was carried out to verify the scaling law for impact force of concentrated impacts. Both mono-disperse and bi-disperse flows were investigated. The particle size and fraction were varied to study their effects on particles breakage and the impact load. Finally, a rock-filled gabion cushioning layer in front of a rigid barrier was modelled to study its ability to attenuate loading from mono-disperse flows.

Load measurements show that the impact force exerted by mono-disperse flows increases with particle size, eventually exceeding the load estimated using the hydrodynamic equation for design. Post-test investigation of particle breakage reveals that flow volume, rather than particle size governs the mechanisms of particle breakage in flows. Flows do not exhibit breakage from direct impact on the barrier. Instead, breakage occurs from collisions among particles. This is because the effective contact stress between particles is up to two times higher than that between a particle and a rigid barrier. Flows enriched with fragments can attenuate the total impact force by up to 40% and induce a higher runup height by up to 30%. Bi-disperse flows dominated by grain-inertial stresses exhibit up to 66% more impulses and 4.3 times more particle breakage. Load measurements from this study show that a 1.2 m thick rock-filled gabion designed using criteria for rock fall protection is sufficient to reduce the impact load transmitted by a cluster of particles to the rigid barrier by up to 93%. The corresponding impact coefficient is back-calculated less than 1.0. The significant load attenuation shows the effectiveness of a rock-filled gabion to mitigate not just a single boulder, but an entire flow comprising boulders.