Dry granular avalanche impact force on a rigid wall: Analytic shock solution versus discrete element simulations

Impacts of Gravitational Mass Movements on Protective Structures—Rock Avalanches/Granular Flow

Rock avalanches and landslides lead to gravitational flow into their runout areas, which poses increasing danger to settlement areas and infrastructure in the Alpine region as a result of climate change. In recent years, a significant increase in extreme events has been registered in the Alps due to climate change. These changes in the threat to settlement areas in the Alpine region have resulted in the need for the construction of sustainable protective structures. Many structures are rigid, but others are now also increasingly flexible, e.g., net and dam structures, which are mainly earth dams with geogrids. In this study, empirical model experiments and numerical simulations were carried out to estimate the flow depth, the deposition forms and the effects on protective structures. Numerical programs usually require unknown input parameters and long computation times for a realistic simulation of the process. This study shows the results of model tests with different granular materials. Furthermore, different design approaches of different authors are presented. Finally, a design model based on the model tests of the University of Innsbruck for rigid barriers, nets and dams due to rock avalanches is presented.

Effects of Barrier Stiffness on Debris Flow Dynamic Impact—II: Numerical Simulation

The destructive and impactful forces of debris flow commonly causes local damage to engineering structures. The effect of a deformable barrier on the impact dynamics is important in engineering design. In this study, a flow–structure coupled with Smoothed Particle Hydrodynamics model was presented to investigate the effects of barrier stiffness on the debris impact. A comparison of the results of physical tests and simulation results revealed that the proposed smoothed particle hydrodynamics model effectively reproduces the flow kinematics and time history of the impact force. Even slight deflections of the deformable barrier lead to obvious attenuation of the peak impact pressure. Additionally, deformable barriers with lower stiffness tend to deform more downstream upon loading, shifting the deposited sand toward the active failure mode and generating less static earth pressure. When the debris flow has a higher frontal velocity, the impact force on the barrier is dominated by the dynamic component and there is an appreciable effect of the stiffness of the deformable barrier on load attenuation.

Measuring jumps during granular chute-flows using X-ray radiography

The present paper describes laboratory tests on steady granular flows down a smooth chute using X-ray radiography. By using an original granular chute set-up with a gate at its end, standing discontinuites in height, velocity and density, namely jumps, were produced during the granular flows. The X-ray radiography was successful to get consistent measurements of the free-surface and density profiles of the flows along the chute under different flow states: the (nearly) uniform flows before the jumps, the gradually-varied flows after the jumps, and the highly non-uniform flows across the jumps. This demonstrates the efficiency of the X-ray radiography to measure granular flows.

Numerical Investigation of Multiple-Impact Behavior of Granular Flow on a Rigid Barrier

The debris–barrier interaction issue has gained considerable attention among the engineering community, but most researches have only focused on the single-surge impact condition, with the multiple-surge impact mechanism still lacking clarity. However, multiple-surge impact is more typical in the field. Thus, we conduct some numerical simulations based on the discrete element method (DEM) and present a series of results that provide preliminary insights into the multiple-surge impact mechanism. The DEM model is firstly calibrated using physical experimental results and then used to investigate the flow kinematics, impact dynamics and energy evolution of the successive impact process. The results indicate that compared with single-surge conditions, the barrier is safer under multiple-surge impact as the deposition spreading distance is extended by 6–20% and the impact force is reduced by 6–30%. The dead zone formed by the previous surge behaves as a cushioning layer and a medium for momentum transfer. Three mechanisms of energy dissipation during surge–dead-zone interactions were identified: friction and penetration at the interaction face between the surge and dead zone, inelastic deformation of the dead zone, and inter-particle interaction within the surge. Each component was analyzed, which shows that inter-particle collision friction accounts for over 60% of the total energy loss during surge–dead-zone interaction. In addition, the performance of granular jump theory in predicting the multiple-surge impact force is assessed, and some possible modifications are proposed. Finally, some engineering implications from the presented numerical results are discussed.